Latest Publications
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Abstract
This paper investigates the impact of fuel distribution on flame stabilization and local combustion modes in a cavity-based scramjet. Two injection schemes with a global equivalence ratio of 0.4 are comparatively studied. Ethylene is injected only from upstream of the cavity in the first case, whereas in the second case 75% of the fuel is injected from upstream of the …show moreThis paper investigates the impact of fuel distribution on flame stabilization and local combustion modes in a cavity-based scramjet. Two injection schemes with a global equivalence ratio of 0.4 are comparatively studied. Ethylene is injected only from upstream of the cavity in the first case, whereas in the second case 75% of the fuel is injected from upstream of the cavity and 25% of the fuel is injected from the cavity floor. The reactive flow in the scramjet is numerically investigated using a hybrid RANS/LES method. The agreement between calculation results and experimentally measured pressure profiles and CH* chemiluminescence images is good. The simulation results are further employed to gain a fundamental understanding of local combustion modes from different aspects: supersonic vs. subsonic, and premixed (fuel-rich vs. fuel-lean) vs. diffusion by using filter functions. In the upstream-only fueling case, it is found that the flame is stabilized by the cavity shear layer and most of the heat is released by supersonic-premixed combustion. Moreover, subsonic-premixed combustion and supersonic-diffusion combustion are significant, and the leading mode changes along the combustor. In the dual fueling case, a cavity assisted jet-wake stabilized flame is observed with higher combustion efficiency. Diffusion combustion becomes the dominant mode, with similar heat release in subsonic and supersonic regions. Nevertheless, the flashback of a premixed flame along the walls plays an important role, leading to diffusion combustion around the fuel jet. The results elucidate the link between the fuel injection schemes, flame stabilization locations, and local combustion modes. show less
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Abstract
Water electrolysis is a promising approach toward low-cost renewable fuels; however, the high overpotential and slow kinetics limit its applicability. Studies suggest that either dinuclear copper (Cu) centers or the use of borate buffer can lead to efficient catalysis. We previously demonstrated the ability of peptoids-N-substituted glycine oligomers-to stabilize …show moreWater electrolysis is a promising approach toward low-cost renewable fuels; however, the high overpotential and slow kinetics limit its applicability. Studies suggest that either dinuclear copper (Cu) centers or the use of borate buffer can lead to efficient catalysis. We previously demonstrated the ability of peptoids-N-substituted glycine oligomers-to stabilize high-oxidation-state metal ions and to form self-assembled di-copper-peptoid complexes. Capitalizing on these features herein we report on a unique Cu-peptoid duplex, Cu2(BEE)2, that is a fast and stable homogeneous electrocatalyst for water oxidation in borate buffer at pH 9.35, with low overpotential and a high turnover frequency of 129 s-1 (peak current measurements) or 5503 s-1 (FOWA); both are the highest reported for Cu-based water electrocatalysts to date. BEE is a peptoid trimer having one 2,2'-bipyridine ligand and two ethanolic groups, easily synthesized on solid support. Cu2(BEE)2 was characterized by single-crystal X-ray diffraction and various spectroscopic and electrochemical techniques, demonstrating its ability to maintain stable in four cycles of controlled potential electrolysis, leading to a high overall turnover number of 51.4 in a total of 2 h. Interestingly, the catalytic activity of control complexes having only one ethanolic side chain is 2 orders of magnitude lower than that of Cu2(BEE)2. On the basis of this comparison and on mechanistic studies, we propose that the ethanolic side chains and the borate buffer have significant roles in the high stability and catalytic activity of Cu2(BEE)2; the -OH groups facilitate protons transfer, while the borate species enables oxygen transfer toward O-O bond formation. show less
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Abstract
The polycrystalline nature of perovskite thin films suggests that the nonradiative recombination losses may be grain size dependent. We use measured grain size distributions of methylammonium lead triiodide layers to describe the macroscopic solar cell as composed of multiple single grain size cells operating in parallel. Using a model, we show that the grain size …show moreThe polycrystalline nature of perovskite thin films suggests that the nonradiative recombination losses may be grain size dependent. We use measured grain size distributions of methylammonium lead triiodide layers to describe the macroscopic solar cell as composed of multiple single grain size cells operating in parallel. Using a model, we show that the grain size distribution results in spatial dispersion of the local open-circuit voltage (0.9–1.15 V), fill factor (50–82%), and power conversion efficiency (7.5–19%). When the device is held at open-circuit voltage, there is significant current exchange between large and small grains. Smaller grains are a “parasitic shunt” for the larger grains. show less
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Abstract
Redox flow batteries are an emerging technology for stationary, grid-scale energy storage. Membraneless batteries in particular are explored as a means to reduce battery cost and complexity. Here, a mathematical model is presented for a membraneless electrochemical cell employing a single laminar flow between electrodes, consisting of a continuous, reactant-poor aqueous …show moreRedox flow batteries are an emerging technology for stationary, grid-scale energy storage. Membraneless batteries in particular are explored as a means to reduce battery cost and complexity. Here, a mathematical model is presented for a membraneless electrochemical cell employing a single laminar flow between electrodes, consisting of a continuous, reactant-poor aqueous phase and a dispersed, reactant-rich nonaqueous phase, and in the absence of gravitational effects. Analytical approximations and numerical solutions for the concentration profile and current-voltage relation are derived via boundary layer analysis. Regimes of slow and fast reactant transport between phases are investigated, and the theory is applied to a membraneless zinc-bromine single-flow battery with multiphase flow. The regime of fast interphase reactant (bromine) transport is characterized by the negligible effect of advection within the cathode boundary layer, leading to a thin boundary layer whose size is largely independent of position, and by relatively high battery current capability. Increasing the nonaqueous (polybromide) phase volume fraction is shown to significantly improve battery performance, as has been observed in recent experiments. For the case of spherical polybromide droplets, the contribution of bromine release from the polybromide phase on the limiting current density becomes negligible for diameters above a critical droplet diameter, when the system can be characterized as having a slow interphase bromine transport. Overall, we show that our analytical approximations agree well with numerical solutions and thus establish a useful theoretical framework for single-flow batteries with multiphase flow. show less
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Ido Caspy,
Ehud Neumann,
Maria Fadeeva,
Varda Liveanu,
Anton Savitsky,
Anna Frank,
Yael Levi-Kalisman,
Yoel Shkolnisky,
Omer Murik,
Haim Treves,
Volker Hartmann,
Marc M Nowaczyk,
Wolfgang Schuhmann,
Matthias Rögner,
Itamar Willner,
Aaron Kaplan,
Gadi Schuster,
Nathan Nelson,
Wolfgang Lubitz,
Rachel Nechushtai
Abstract
Photosynthesis in deserts is challenging since it requires fast adaptation to rapid night-to-day changes, that is, from dawn’s low light (LL) to extreme high light (HL) intensities during the daytime. To understand these adaptation mechanisms, we purified photosystem I (PSI) from Chlorella ohadii, a green alga that was isolated from a desert soil crust, and …show morePhotosynthesis in deserts is challenging since it requires fast adaptation to rapid night-to-day changes, that is, from dawn’s low light (LL) to extreme high light (HL) intensities during the daytime. To understand these adaptation mechanisms, we purified photosystem I (PSI) from Chlorella ohadii, a green alga that was isolated from a desert soil crust, and identified the essential functional and structural changes that enable the photosystem to perform photosynthesis under extreme high light conditions. The cryo-electron microscopy structures of PSI from cells grown under low light (PSILL) and high light (PSIHL), obtained at 2.70 and 2.71 Å, respectively, show that part of light-harvesting antenna complex I (LHCI) and the core complex subunit (PsaO) are eliminated from PSIHL to minimize the photodamage. An additional change is in the pigment composition and their number in LHCIHL; about 50% of chlorophyll b is replaced by chlorophyll a. This leads to higher electron transfer rates in PSIHL and might enable C. ohadii PSI to act as a natural photosynthesiser in photobiocatalytic systems. PSIHL or PSILL were attached to an electrode and their induced photocurrent was determined. To obtain photocurrents comparable with PSIHL, 25 times the amount of PSILL was required, demonstrating the high efficiency of PSIHL. Hence, we suggest that C. ohadii PSIHL is an ideal candidate for the design of desert artificial photobiocatalytic systems. show less
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Abstract
Anion-exchange membrane fuel cells (AEMFCs) show substantially enhanced (initial) performance and efficiency with the increase of operational temperature (where typical values are below 80 °C). This is directly due to the increase in reaction and mass transfer rates with temperature. Common sense suggests however that the increase of ionomeric material chemical …show moreAnion-exchange membrane fuel cells (AEMFCs) show substantially enhanced (initial) performance and efficiency with the increase of operational temperature (where typical values are below 80 °C). This is directly due to the increase in reaction and mass transfer rates with temperature. Common sense suggests however that the increase of ionomeric material chemical degradation kinetics with temperature is likely to offset the above mentioned gain in performance and efficiency. In this computational study we investigate the combined effect of a high operating temperature, up to 120 °C, on the performance and stability of AEMFCs. Our modeling results demonstrate the expected positive impact of operating temperature on AEMFC performance. More interestingly, under certain conditions, AEMFC performance stability is surprisingly enhanced as temperature increases. While increasing cell temperature enhances degradation kinetics, it simultaneously improves water diffusivity through the membrane, resulting in higher hydration levels at the cathode. This, in turn, encourages a decrease in ionomer chemical degradation which depends on the hydration as well as on temperature, leading to a significant increase in AEMFC performance stability and, therefore, in its lifetime. These findings predict the possible advantage (and importance), in terms of performance and durability, of developing high-temperature AEMFCs for automotive and other applications. show less
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Abstract
Cadmium chalcogenides–metal hybrid nanostructures play an important role in a wide range of applications and are key components in photocatalysis. Hence, great efforts have been devoted to the exploration of a variety of metal components, each offering different functionalities. Silver is a vital catalyst used in the production of major industrial chemicals, found in …show moreCadmium chalcogenides–metal hybrid nanostructures play an important role in a wide range of applications and are key components in photocatalysis. Hence, great efforts have been devoted to the exploration of a variety of metal components, each offering different functionalities. Silver is a vital catalyst used in the production of major industrial chemicals, found in virtually every electronic device, widely exploited as an antibacterial agent, used in fuel cells, and has been extensively investigated for CO2 reduction. Yet, silver nanoparticles were not utilized in conjunction with cadmium chalcogenide colloidal nanostructures due to the tendency of Ag+ to undergo cation exchange. We present here a new strategy that opens up a pathway for avoiding cation exchange and obtaining metallic silver tipping on cadmium chalcogenide nanorods. The formation of Ag trioctylphosphine complex, as an intermediate in the course of Ag deposition on nanorods, was identified to be a critical step, which prevents undesirable cation exchange. Metallic Ag was confirmed by several advanced techniques and its growth location on the tip of nanorods was carefully studied. Moderate control over the crystalline Ag tip size was demonstrated in the range of 1.5–5.4 nm. show less
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Weikang Zhu,
Yabiao Pei,
John C Douglin,
Junfeng Zhang,
Haoyang Zhao,
Jiandang Xue,
Qingfa Wang,
Ran Li,
Yanzhou Qin,
Yan Yin,
Dario R Dekel,
Michael D Guiver
Abstract
Recently, much work has been devoted to designing catalysts with high porosity and efficient active sites. Although very promising results are achieved using Co/Fe–N–C catalysts based on rotating disk electrode (RDE) tests, actual fuel cell performance is below expectations, probably due to insufficient understanding of the catalyst layer (CL). Therefore, catalyst design …show moreRecently, much work has been devoted to designing catalysts with high porosity and efficient active sites. Although very promising results are achieved using Co/Fe–N–C catalysts based on rotating disk electrode (RDE) tests, actual fuel cell performance is below expectations, probably due to insufficient understanding of the catalyst layer (CL). Therefore, catalyst design should be considered holistically by taking into account CL performance, not only intrinsic activity. Here, Co/Fe–N–C with highly dispersed CoFe nanoalloy in the carbon network is obtained by careful design of Co/Fe-ZIF precursor, resulting in a high oxygen reduction reaction (ORR) site density with good stability. Concerning RDE test in the kinetic region and single cell test (SCT) with complex influence factors, the half-cell test (HCT) is introduced to more accurately evaluate the quality of the Co/Fe–CL. Multi-scale measurements (RDE, HCT and SCT) in different current density ranges allows targeting the key CL influence factors for fuel cell performance. show less
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Yogesh Kumar,
Elo Kibena-Põldsepp,
Jekaterina Kozlova,
Mihkel Rähn,
Alexey Treshchalov,
Arvo Kikas,
Vambola Kisand,
Jaan Aruväli,
Aile Tamm,
John C Douglin,
Scott J Folkman,
Ilario Gelmetti,
Felipe A Garcés-Pineda,
José Ramón Galán-Mascarós,
Dario R Dekel,
Kaido Tammeveski
Abstract
Non-precious-metal catalysts are promising alternatives for Pt-based cathode materials in low-temperature fuel cells, which is of great environmental importance. Here, we have investigated the bifunctional electrocatalytic activity toward the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of mixed metal (FeNi; FeMn; FeCo) phthalocyanine-modified …show moreNon-precious-metal catalysts are promising alternatives for Pt-based cathode materials in low-temperature fuel cells, which is of great environmental importance. Here, we have investigated the bifunctional electrocatalytic activity toward the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of mixed metal (FeNi; FeMn; FeCo) phthalocyanine-modified multiwalled carbon nanotubes (MWCNTs) prepared by a simple pyrolysis method. Among the bimetallic catalysts containing nitrogen derived from corresponding metal phthalocyanines, we report the excellent ORR activity of FeCoN-MWCNT and FeMnN-MWCNT catalysts with the ORR onset potential of 0.93 V and FeNiN-MWCNT catalyst for the OER having EOER = 1.58 V at 10 mA cm–2. The surface morphology, structure, and elemental composition of the prepared catalysts were examined with scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The FeCoN-MWCNT and FeMnN-MWCNT catalysts were prepared as cathodes and tested in anion-exchange membrane fuel cells (AEMFCs). Both catalysts displayed remarkable AEMFC performance with a peak power density as high as 692 mW cm–2 for FeCoN-MWCNT. show less
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Abstract
The study of nanocrystal self-assembly into superlattices or superstructures is of great significance in nanoscience. Carbon nitride quantum dots (CNQDs), being a promising new group of nanomaterials, however, have hardly been explored in their self-organizing behavior. Here we report of a unique irradiation-triggered self-assembly and recrystallization phenomenon of …show moreThe study of nanocrystal self-assembly into superlattices or superstructures is of great significance in nanoscience. Carbon nitride quantum dots (CNQDs), being a promising new group of nanomaterials, however, have hardly been explored in their self-organizing behavior. Here we report of a unique irradiation-triggered self-assembly and recrystallization phenomenon of crystalline CNQDs (c-CNQDs) terminated by abundant oxygen-containing groups. Unlike the conventional self-assembly of nanocrystals into ordered superstructures, the photoinduced self-assembly of c-CNQDs resembles a "click reaction" process of macromolecules, in which the activated -OH and -NH 2 functional groups along the perimeters initiate cross-linking of adjacent QDs through a photocatalytic effect. Our findings unveil fundamental physiochemical features of CNQDs and open up new possibilities of manipulating carbon nitride nanomaterials via controlled assembly. Prospects for potential applications are discussed as well. show less
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Abstract
Stable complexes with terminal triply bound metal-oxygen bonds are usually not considered as valuable catalysts for the hydrogen evolution reaction (HER). We now report the preparation of three conceptually different (oxo)molybdenum(V) corroles for testing if proton-assisted 2-electron reduction will lead to hyper-reactive molybdenum(III) capable of converting protons …show moreStable complexes with terminal triply bound metal-oxygen bonds are usually not considered as valuable catalysts for the hydrogen evolution reaction (HER). We now report the preparation of three conceptually different (oxo)molybdenum(V) corroles for testing if proton-assisted 2-electron reduction will lead to hyper-reactive molybdenum(III) capable of converting protons to hydrogen gas. The upto 670 mV differences in the [(oxo)Mo(IV)]-/[(oxo)Mo(III)]−2 redox potentials of the dissolved complexes came into effect by the catalytic onset potential for proton reduction thereby, significantly earlier than their reduction process in the absence of acids, but the two more promising complexes were not stable at practical conditions. Under heterogeneous conditions, the smallest and most electron-withdrawing catalyst did excel by all relevant criteria, including a 97% Faradaic efficiency for catalyzing HER from acidic water. This suggests complexes based on molybdenum, the only sustainable heavy transition metal, as catalysts for other yet unexplored green-energy-relevant processes. show less
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Abstract
A most important endeavor in modern materials' research is the current shift toward green environmental and sustainable materials. Natural resources are one of the attractive building blocks for making environmentally friendly materials. In most cases, however, the performance of nature-derived materials is inferior to the performance of carefully designed synthetic …show moreA most important endeavor in modern materials' research is the current shift toward green environmental and sustainable materials. Natural resources are one of the attractive building blocks for making environmentally friendly materials. In most cases, however, the performance of nature-derived materials is inferior to the performance of carefully designed synthetic materials. This is especially true for conductive polymers, which is the topic here. Inspired by the natural role of proteins in mediating protons, their utilization in the creation of a free-standing transparent polymer with a highly elastic nature and proton conductivity comparable to that of synthetic polymers, is demonstrated. Importantly, the polymerization process relies on natural protein crosslinkers and is spontaneous and energy-efficient. The protein used, bovine serum albumin, is one of the most affordable proteins, resulting in the ability to create large-scale materials at a low cost. Due to the inherent biodegradability and biocompatibility of the elastomer, it is promising for biomedical applications. Here, its immediate utilization as a solid-state interface for sensing of electrophysiological signals, is shown. show less
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Abstract
Flavin-dependent glucose dehydrogenases (FAD-GDH) are oxygen-independent enzymes with high potential to be used as biocatalysts in glucose biosensing applications. Here, we present the construction of an amperometric biosensor and a biofuel cell device, which are based on a thermophilic variant of the enzyme originated from Talaromyces emersonii. The enzyme overexpression …show moreFlavin-dependent glucose dehydrogenases (FAD-GDH) are oxygen-independent enzymes with high potential to be used as biocatalysts in glucose biosensing applications. Here, we present the construction of an amperometric biosensor and a biofuel cell device, which are based on a thermophilic variant of the enzyme originated from Talaromyces emersonii. The enzyme overexpression in Escherichia coli and its isolation and performance in terms of maximal bioelectrocatalytic currents were evaluated. We examined the biosensor's bioelectrocatalytic activity in 2,6-dichlorophenolindophenol-, thionine-, and dichloro-naphthoquinone-mediated electron transfer configurations or in a direct electron transfer one. We showed a negligible interference effect and good stability for at least 20 h for the dichloro-naphthoquinone configuration. The constructed biosensor was also tested in interstitial fluid-like solutions to show high bioelectrocatalytic current responses. The bioanode was coupled with a bilirubin oxidase-based biocathode to generate 270 μW/cm2 in a biofuel cell device. show less
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Abstract
Despite the increasing demand for enantiopure drugs in the pharmaceutical industry, currently available chiral separation technologies are still lagging behind, whether due to throughput or to operability considerations. This paper presents a new kinetic resolution method, based on the specific adsorption of a target enantiomer onto a molecularly imprinted surface of …show moreDespite the increasing demand for enantiopure drugs in the pharmaceutical industry, currently available chiral separation technologies are still lagging behind, whether due to throughput or to operability considerations. This paper presents a new kinetic resolution method, based on the specific adsorption of a target enantiomer onto a molecularly imprinted surface of a photocatalyst and its subsequent degradation through a photocatalytic mechanism. The current model system is composed of an active TiO2 layer, on which the target enantiomer is adsorbed. A photocatalytic suppression layer of Al2O3 is then grown around the adsorbed target molecules by atomic layer deposition. Following the removal of the templating molecules, molecularly imprinted cavities that correspond to the adsorbed species are formed. The stereospecific nature of these pores encourages enantioselective degradation of the undesired species through its enhanced adsorption on the photocatalyst surface, while dampening nonselective photocatalytic activity around the imprinted sites. The method, demonstrated with the dipeptide leucylglycine as a model system, revealed a selectivity factor of up to 7 and an enrichment of a single enantiomer to 85% from an initially racemic mixture. The wide range of parameters that can be optimized (photocatalyst, concentration of imprinted sites, type of passivating layer, etc.) points to the great potential of this method for obtaining enantiomerically pure compounds, beginning from racemic mixtures. show less
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Bo Zhao,
Sid Assawaworrarit,
Parthiban Santhanam,
Meir Orenstein,
Shanhui Fan
Abstract
Direct current (DC) converters play an essential role in electronic circuits. Conventional high-efficiency DC voltage converters, especially step-up type, rely on switching operation, where energy is periodically stored within and released from inductors and/or capacitors connected in a variety of circuit topologies. Since these energy storage components, especially …show moreDirect current (DC) converters play an essential role in electronic circuits. Conventional high-efficiency DC voltage converters, especially step-up type, rely on switching operation, where energy is periodically stored within and released from inductors and/or capacitors connected in a variety of circuit topologies. Since these energy storage components, especially inductors, are fundamentally difficult to scale down, miniaturization of switching converters proves challenging. Furthermore, the resulting switching currents produce significant electromagnetic noise. To overcome the limitations of switching converters, photonic transformers, where voltage conversion is achieved through light emission and detection processes, have been demonstrated. However, the demonstrated efficiency is significantly below that of the switching converter. Here we perform a detailed balance analysis and show that with a monolithically integrated design that enables efficient photon transport, the photonic transformer can operate with a near-unity conversion efficiency and high voltage conversion ratio. We validate the theory with a transformer constructed with off-the-shelf discrete components. Our experiment showcases near noiseless operation and a voltage conversion ratio that is significantly higher than obtained in previous photonic transformers. Our findings point to the possibility of a high-performance optical solution to miniaturizing DC power converters and improving the electromagnetic compatibility and quality of electrical power. Conventional DC-DC converters rely on switching operations and energy storing components which face both noise and scaling difficulties. Here, the authors present an alternative design for a DC-to-DC converter based on closely coupled LEDs and photovoltaic cells, which exhibits high efficiency, low noise, and miniaturizability. show less
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Abstract
Microbial rhodopsins are diverse photoreceptive proteins containing a retinal chromophore and are found in all domains of cellular life and are even encoded in genomes of viruses. These rhodopsins make up two families: type 1 rhodopsins and the recently discovered heliorhodopsins. These families have seven transmembrane helices with similar structures but opposing …show moreMicrobial rhodopsins are diverse photoreceptive proteins containing a retinal chromophore and are found in all domains of cellular life and are even encoded in genomes of viruses. These rhodopsins make up two families: type 1 rhodopsins and the recently discovered heliorhodopsins. These families have seven transmembrane helices with similar structures but opposing membrane orientation. Microbial rhodopsins participate in a portfolio of light-driven energy and sensory transduction processes. In this review we present data collected over the last two decades about these rhodopsins and describe their diversity, functions, and biological and ecological roles. show less
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Ananya Maddegalla,
Ayan Mukherjee,
J Alberto Blázquez,
Eneko Azaceta,
Olatz Leonet,
Aroa R Mainar,
Aleksey Kovalevsky,
Daniel Sharon,
Jean-Frédéric Martin,
Dane Sotta,
Yair Ein-Eli,
Doron Aurbach,
Malachi Noked
Abstract
In recent decades rechargeable Mg batteries (RMB) technologies have attracted much attention because the use of thin Mg foils anodes may enable to develop high energy density batteries. One of the most critical challenges for devolving RMB is finding suitable electrolyte solutions that enable efficient and reversible Mg cells operation. Most RMB studies concentrate …show moreIn recent decades rechargeable Mg batteries (RMB) technologies have attracted much attention because the use of thin Mg foils anodes may enable to develop high energy density batteries. One of the most critical challenges for devolving RMB is finding suitable electrolyte solutions that enable efficient and reversible Mg cells operation. Most RMB studies concentrate on the development of novel electrolyte systems, while only few studies have focused on the practical feasibility of using pure metallic Mg as the anode material. Pure Mg metal anodes have been demonstrated to be useful in studying the fundamentals of nonaqueous Mg electrochemistry. However, pure Mg metal may not be suitable for mass production of ultrathin foils (< 100 microns) due to its limited ductility. The metals industry overcomes this problem by using ductile Mg alloys. We demonstrate herein the feasibility of processing ultrathin Mg anodes in electrochemical cells by using AZ31 Mg alloys (3% Al; 1% Zn). Thin film Mg AZ31 anodes present reversible Mg dissolution and deposition behavior in complex ethereal Mg electrolytes solutions that is comparable to that of pure Mg foils. Moreover, we demonstrated that secondary Mg battery prototypes comprising ultrathin AZ31 Mg alloy anodes (≈ 25 µm thick) and Mg x Mo 6 S 8 Chevrel phase cathodes exhibit cycling performance that is equal to that of similar cells containing thicker pure Mg foil anodes. The possibility of using of ultrathin processable Mg metal anodes is an important step in the realization of rechargeable Mg batteries. show less
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Abstract
The flow field of an impulsively started round, confined nitrogen jet was investigated using combined high speed schlieren imaging and particle velocimetry (PIV) measurements. PIV measurements were carried out at five different, normalized times (55 ≤t∗≤ 392) relative to jet intrusion into a constant volume chamber. Between 100 …show moreThe flow field of an impulsively started round, confined nitrogen jet was investigated using combined high speed schlieren imaging and particle velocimetry (PIV) measurements. PIV measurements were carried out at five different, normalized times (55 ≤t∗≤ 392) relative to jet intrusion into a constant volume chamber. Between 100 < t∗ < 250, the NPR linearly increased to that for a moderately underexpanded jet (NPR ≈ 3.5). Distributions of the mean flow and Reynolds normal and shear stresses revealed two different stages in jet development. In stage I (t∗ = 55–103), prior to clear shock cell appearance, the jet was characterized by a leading, toroidal vortex whose induced recirculatory motion inhibited the growth of the trailing jet's shear layer instabilities and radial spreading. In stage II (t∗ = 196 and 392), the jet became moderately underexpanded (NPR ≥ 2) and close to the nozzle exit, flow characteristics resembled those of a “co-annular” jet. The co-annular region did not extend beyond 15 D. An analysis of instantaneous vortex numbers and strengths further supported the two identified stages in jet development and their connection to shear layer instability growth. Based on the distributions of mean flow and Reynolds stresses, it was shown that the static pressure gradient along the jet's centerline is mainly governed by the dynamic pressure gradient. Gradients of the Reynolds normal and shear stresses play a minor role. Important for gaseous fuel injection at high injection pressures, results point at limited mixing during stage I and enhanced mixing during stage II. show less
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Abstract
Hematite (α-Fe2O3) is a leading photoanode candidate for photoelectrochemical water splitting. Despite extensive research efforts, the champion hematite photoanodes reported to date have achieved less than half of the maximal photocurrent predicted by its bandgap energy. Here we show that this underachievement arises, to a large extent, because of …show moreHematite (α-Fe2O3) is a leading photoanode candidate for photoelectrochemical water splitting. Despite extensive research efforts, the champion hematite photoanodes reported to date have achieved less than half of the maximal photocurrent predicted by its bandgap energy. Here we show that this underachievement arises, to a large extent, because of unproductive optical excitations that give rise to localized electronic transitions that do not generate electron–hole pairs. A comprehensive method for extraction of the photogeneration yield spectrum, the wavelength-dependent fraction of absorbed photons that generate electron–hole pairs, and the spatial charge carrier collection efficiency is presented, and applied for a thin (32 nm) film hematite photoanode. Its photogeneration yield is less than unity across the entire absorption range, limiting the maximal photocurrent that may be attained in an ideal hematite photoanode to about half of the theoretical limit predicted without accounting for this effect. show less
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Abstract
Nature uses proteins for a variety of functions, and among all others, their ability to form high-hierarchical structures as well as to mediate charges. We are inspired by these functions of proteins in nature and utilize proteins for the formation of large-scale conductive materials. We report here on a new family of conductive biopolymers using only sustainable and …show moreNature uses proteins for a variety of functions, and among all others, their ability to form high-hierarchical structures as well as to mediate charges. We are inspired by these functions of proteins in nature and utilize proteins for the formation of large-scale conductive materials. We report here on a new family of conductive biopolymers using only sustainable and abundant proteins. We show that our new biopolymers have superior mechanical properties and ionic conductivity, which is due to their high water uptake and the presence of oxo-amino-acids. We further show that our biopolymers can be easily functionalized in different ways, thus enhancing their ionic conductivity, enabling electron conduction, and introducing optoelectronic properties. We currently use our polymers for making new biosensors. These polymers are environmentally friendly, biodegradable, biocompatible, and low-cost, and we foresee their integration in numerous applications from biomedical to energy applications show less
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Abstract
The COVID-19 pandemic and the preventive measures that followed it have significantly impacted generation and consumption patterns in power systems across the globe, calling for new tools to efficiently evaluate generation and load profiles. In this work, we propose one possible tool, which we name the smoothness index, that evaluates a profile based on both its load …show moreThe COVID-19 pandemic and the preventive measures that followed it have significantly impacted generation and consumption patterns in power systems across the globe, calling for new tools to efficiently evaluate generation and load profiles. In this work, we propose one possible tool, which we name the smoothness index, that evaluates a profile based on both its load factor and ramp rate. The proposed index is a modification of the coefficient of variation, also known as the relative standard deviation, and is computed by transforming the profile under study to the frequency domain, and calculating the weighted norm of the signal, where higher frequencies are associated with larger weights. We demonstrate our method by studying the effects of the COVID-19 pandemic and government policies on load and generation profiles in several European countries. show less
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Abiodun E Onile,
Juri Belikov,
Eduard Petlenkov,
Yoash Levron
Abstract
In the recent years, the impact of urban climate change and ever-expanding needs for electricity energy calls for urgent attention. Generally, electricity can be conserved by implementing efficiency models that handle effective utilization. To set and monitor energy conservation goals at consumer end, this study presents an innovative ranking approach as Demand Side …show moreIn the recent years, the impact of urban climate change and ever-expanding needs for electricity energy calls for urgent attention. Generally, electricity can be conserved by implementing efficiency models that handle effective utilization. To set and monitor energy conservation goals at consumer end, this study presents an innovative ranking approach as Demand Side Management technique for estimating the amount of energy used by consumers toward identifying potential savings. We further present comparative analysis of five unsupervised graph-based ranking techniques such as PageRank, TrustRank, Hyperlink-induced search, Markov chain, and Differential ranking algorithms for proffering suitable solution to energy conservation problems. The various ranking methods were evaluated in the context of consumer-oriented energy services. show less
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Nilanjan Roy Chowdhury,
Dmitry Baimel,
Juri Belikov,
Yoash Levron
Abstract
It is currently observed that rapid changes in generation and consumption can significantly impact the stability of a power system. In this light, this paper proposes a nonlinear feedback strategy for energy storage systems which operates under uncertainty conditions, and does not require statistical representations of future signals. We employ stochastic dynamic …show moreIt is currently observed that rapid changes in generation and consumption can significantly impact the stability of a power system. In this light, this paper proposes a nonlinear feedback strategy for energy storage systems which operates under uncertainty conditions, and does not require statistical representations of future signals. We employ stochastic dynamic programming (SDP) to derive the nonlinear feedback policy and then verify its stability properties using a Lyapunov-based analysis. A central challenge in such problems arises due to the calculation of two-dimensional value functions at each time instant, which requires considerable computational resources. To address this challenge, we consider a quadratic cost function and model the load power as a first-order auto-regressive stochastic process. We show that these considerations help solve the optimal control problem using SDP, and evaluate a feedback policy which is sub-optimal and stable. Numerical experiments reveal that this proposed feedback policy always keeps the stored energy within bounds, and allows it to follow the optimal path. show less
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Abstract
We evaluate near-field thermophotovoltaic (TPV) energy conversion systems focusing in particular on their open-circuit voltage (Voc). Unlike previous analyses based largely on numerical simulations with fluctuational electrodynamics, here, we develop an analytic model that captures the physics of near-field TPV systems and can predict their performance metrics. Using …show moreWe evaluate near-field thermophotovoltaic (TPV) energy conversion systems focusing in particular on their open-circuit voltage (Voc). Unlike previous analyses based largely on numerical simulations with fluctuational electrodynamics, here, we develop an analytic model that captures the physics of near-field TPV systems and can predict their performance metrics. Using our model, we identify two important opportunities of TPV systems operating in the near-field. First, we show analytically that enhancement of radiative recombination is a natural consequence of operating in the near-field. Second, we note that, owing to photon recycling and minimal radiation leakage in near-field operation, the PV cell used in near-field TPV systems can be much thinner compared to those used in solar PV systems. Since non-radiative recombination is a volumetric effect, use of a thinner cell reduces non-radiative losses per unit area. The combination of these two opportunities leads to increasingly large values of Voc as the TPV vacuum gap decreases. Hence, although operation in the near-field was previously perceived to be beneficial for electrical power density enhancement, here, we emphasize that thin-film near-field TPVs are also significantly advantageous in terms of Voc and consequently conversion efficiency as well as power density. We provide numerical results for an InAs-based thin-film TPV that exhibits efficiency > 50% at an emitter temperature as low as 1100 K. show less
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Abstract
Fuel cell (FC) is an attractive green alternative for today's fuel combustion systems. In common FCs, a polymer electrolyte membrane selectively conducts protons but blocks the passage of electrons and fuel. Nafion, the current benchmark membrane material, has a superior conductivity owing to unique morphology comprising randomly oriented elongated ionic nanochannels …show moreFuel cell (FC) is an attractive green alternative for today's fuel combustion systems. In common FCs, a polymer electrolyte membrane selectively conducts protons but blocks the passage of electrons and fuel. Nafion, the current benchmark membrane material, has a superior conductivity owing to unique morphology comprising randomly oriented elongated ionic nanochannels within its Teflon-like matrix. Channel orientation enhances Nafion conductivity, yet there has been no facile method to induce a stable alignment in the desired through-plane (TP) direction. Here, we report an approach based on dual electrospun Nafion-PVDF nanofiber composites that yields a stable TP alignment. It utilizes extreme thinness and strong inherent orientation within electrospun nanofibers, which is readily converted to TP alignment by plunging an electrospun nanofiber mat into a thin slit, resulting in nanofiber buckling and subsequent consolidation. Using TEM and SAXS, we demonstrate a pronounced and sustained TP ion channel orientation in prepared membranes, yielding a highly anisotropic swelling and conductivity exceeding that of bulk Nafion when normalized to Nafion content. The analysis also highlights the importance of PVDF as a stabilizing component, preserving orientation upon annealing, while a similarly prepared pure Nafion membrane loses anisotropy. The approach holds potential to advance the FC technology by overcoming current limitations of ionomeric membranes. show less
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Abstract
Long–range structures and dynamics are central to coordination chemistry, yet are hard to identify experimentally. By combining polarized low-frequency Raman spectroscopy with single crystal XRD to study barium nitrilotriacetate, a metal–organic coordination polymer and a useful pyrolysis precursor, we could assign Raman peaks experimentally to layer shear motions and …show moreLong–range structures and dynamics are central to coordination chemistry, yet are hard to identify experimentally. By combining polarized low-frequency Raman spectroscopy with single crystal XRD to study barium nitrilotriacetate, a metal–organic coordination polymer and a useful pyrolysis precursor, we could assign Raman peaks experimentally to layer shear motions and perpendicular hydrogen bond vibrations. These directional long–range interactions further determined the preferred fracture directions during crystallization, establishing an important link between structural motifs in the precursor, and the porosity of the carbon it yields upon pyrolysis. show less
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Manuel Weiss,
Raffael Ruess,
Johannes Kasnatscheew,
Yehonatan Levartovsky,
Natasha Ronith Levy,
Philip Minnmann,
Lukas Stolz,
Thomas Waldmann,
Margret Wohlfahrt-Mehrens,
Doron Aurbach,
Martin Winter,
Yair Ein-Eli,
Jürgen Janek
Abstract
Fast charging is considered to be a key requirement for widespread economic success of electric vehicles. Current lithium-ion batteries (LIBs) offer high energy density enabling sufficient driving range, but take considerably longer to recharge than traditional vehicles. Multiple properties of the applied anode, cathode, and electrolyte materials influence the fast-charging …show moreFast charging is considered to be a key requirement for widespread economic success of electric vehicles. Current lithium-ion batteries (LIBs) offer high energy density enabling sufficient driving range, but take considerably longer to recharge than traditional vehicles. Multiple properties of the applied anode, cathode, and electrolyte materials influence the fast-charging ability of a battery cell. In this review, the physicochemical basics of different material combinations are considered in detail, identifying the transport of lithium inside the electrodes as the crucial rate-limiting steps for fast-charging. Lithium diffusion within the active materials inherently slows down the charging process and causes high overpotentials. In addition, concentration polarization by slow lithium-ion transport within the electrolyte phase in the porous electrodes also limits the charging rate. Both kinetic effects are responsible for lithium plating observed on graphite anodes. Conclusions drawn from potential and concentration profiles within LIB cells are complemented by extensive literature surveys on anode, cathode, and electrolyte materials—including solid-state batteries. The advantages and disadvantages of typical LIB materials are analyzed, resulting in suggestions for optimum properties on the material and electrode level for fast-charging applications. Finally, limitations on the cell level are discussed briefly as well. show less
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Abstract
Future expansion of corn-derived ethanol raises concerns of sustainability and competition with the food industry. Therefore, cellulosic biofuels derived from agricultural waste and dedicated energy crops are necessary. To date, slow and incomplete saccharification as well as high enzyme costs have hindered the economic viability of cellulosic biofuels, and while …show moreFuture expansion of corn-derived ethanol raises concerns of sustainability and competition with the food industry. Therefore, cellulosic biofuels derived from agricultural waste and dedicated energy crops are necessary. To date, slow and incomplete saccharification as well as high enzyme costs have hindered the economic viability of cellulosic biofuels, and while approaches like simultaneous saccharification and fermentation (SSF) and the use of thermotolerant microorganisms can enhance production, further improvements are needed. Cellulosic emulsions have been shown to enhance saccharification by increasing enzyme contact with cellulose fibers. In this study, we use these emulsions to develop an emulsified SSF (eSSF) process for rapid and efficient cellulosic biofuel production and make a direct three-way comparison of ethanol production between S. cerevisiae, O. polymorpha, and K. marxianus in glucose and cellulosic media at different temperatures. show less
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Abstract
An intrinsic challenge of Li-ion batteries is the instability of electrolytes against anode materials. For anodes with a favorably low operating potential, a solid-electrolyte interphase (SEI) formed during initial cycles provides stability, traded off for capacity consumption. The SEI is mainly determined by the anode material, electrolyte composition, and formation …show moreAn intrinsic challenge of Li-ion batteries is the instability of electrolytes against anode materials. For anodes with a favorably low operating potential, a solid-electrolyte interphase (SEI) formed during initial cycles provides stability, traded off for capacity consumption. The SEI is mainly determined by the anode material, electrolyte composition, and formation conditions. Its properties are typically adjusted by changing the liquid electrolyte's composition. Artificial SEIs (Art-SEIs) offer much more freedom to address and tune specific properties, such as chemical composition, impedance, thickness, and elasticity. Art-SEIs for intercalation, alloying, conversion and Li metal anodes have to fulfil varying requirements. In all cases, sufficient transport properties for Li-ions and (electro-)chemical stability must be guaranteed. Several approaches for Art-SEIs preparation have been reported: from simple casting and coating techniques to elaborated Phys-Chem modifications and deposition processes. This review critically reports on the promising approaches for Art-SEIs formation on different type of anode materials, focusing on methodological aspects. The specific requirements for each approach and material class, as well as the most effective strategies for Art-SEI coating, are discussed and a roadmap for further developments towards next-generation stable anodes are provided. show less
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Abstract
Flow-electrode capacitive deionization (FCDI), as a novel electro-driven desalination technology, has attracted growing exploration towards brackish water treatment, hypersaline water treatment, and selective resource recovery in recent years. As a flow-electrode-based electrochemical technology, FCDI has similarities with several other electrochemical technologies such …show moreFlow-electrode capacitive deionization (FCDI), as a novel electro-driven desalination technology, has attracted growing exploration towards brackish water treatment, hypersaline water treatment, and selective resource recovery in recent years. As a flow-electrode-based electrochemical technology, FCDI has similarities with several other electrochemical technologies such as electrochemical flow capacitors and semi-solid fuel cells, whose performance are closely coupled with the characteristics of the flow-electrodes. In this review, we sort out the potentially parallel mechanisms of electrosorption and electrodialysis in the FCDI desalination process, and make clear the importance of the flowable capacitive electrodes. We then adopt an equivalent circuit model to distinguish the resistances to ion transport and electron transport within the electrodes, and clarify the importance of electronic conductivity on the system performance based on a series of electrochemical tests. Furthermore, we discuss the effects of electrode selection and flow circulation patterns on system performance (energy consumption, salt removal rate), review the current treatment targets and system performance, and then provide an outlook on the research directions in the field to support further applications of FCDI. show less
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Abstract
We present a first high-temperature anion-exchange membrane fuel cell (HT-AEMFC, operating at 105 °C) based on a critical raw material (CRM)-free cathode catalyst; at the same temperature, the anion-exchange membrane (AEM) has a high ex-situ hydroxide conductivity value of 201 mS cm−1. Our HT-AEMFC, containing a highly active nitrogen-doped carbon (N-doped-C) …show moreWe present a first high-temperature anion-exchange membrane fuel cell (HT-AEMFC, operating at 105 °C) based on a critical raw material (CRM)-free cathode catalyst; at the same temperature, the anion-exchange membrane (AEM) has a high ex-situ hydroxide conductivity value of 201 mS cm−1. Our HT-AEMFC, containing a highly active nitrogen-doped carbon (N-doped-C) cathode catalyst, also features low polarization resistances, high catalytic activity and stability, with retention of 81% of the catalyst layer capacitance after an initial 10 h longevity test, and delivery of a peak power of 1.14 W cm−2. This is one of the highest power densities reported for an AEMFC containing a CRM-free cathode. This work shows the potential of the new field of HT-AEMFCs, opening opportunities for developing and using novel CRM-free catalysts that are highly active at these high operating temperatures. show less
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Abstract
The conversion of biomass and other cellulose-based materials to clean energy has high promise for a sustainable world. Herein we present a green methodology to convert cellulose directly into electrical power output by utilizing cellulase complex and an enzymatic biofuel cell. An integrated FAD-dependent glucose dehydrogenase (FAD-GDH) based anode and a bilirubin …show moreThe conversion of biomass and other cellulose-based materials to clean energy has high promise for a sustainable world. Herein we present a green methodology to convert cellulose directly into electrical power output by utilizing cellulase complex and an enzymatic biofuel cell. An integrated FAD-dependent glucose dehydrogenase (FAD-GDH) based anode and a bilirubin oxidase-based cathode were used for the cell construction. Cellulase complex was utilized for the cellulose to glucose degradation which was then oxidized by the FAD-GDH based anode to generate bioelectrocatalytic currents. The generated electrons were subsequently transferred to a bilirubin oxidase-based cathode for the oxygen reduction reaction. The designed biofuel cell allows direct biomass to electricity conversion, operating under neutral pH and standard conditions. The constructed biofuel cell was optimized under different cell conditions and a maximal operational lifetime of 32 hours was achieved. The optimized cell reached an electrical power of ∼300 μW cm−2 and 600 μW cm−2 under atmospheric and oxygen saturated conditions, respectively. Overall, the introduced one-pot biofuel cell allows the generation of bias-free electrical power while only cellulose and O2 are required for its operation. show less
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Abstract
Fabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition …show moreFabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition of inorganic compounds' atomic layer deposition (ALD) aiming to enhance cycling performance of supercapacitors and battery electrodes can be applied to the AC electrode materials. Here, we report on the investigation of zinc oxide (ZnO) coating strategy in terms of different pulse times of precursors, ALD cycles, and deposition temperatures to ensure high electrical conductivity and capacitance retention without blocking the micropores of the AC electrode. Crystalline ZnO phase with its optimal forming condition is obtained preferably using a longer precursor pulse time. Supercapacitors comprising AC electrodes coated with 20 cycles of ALD ZnO at 70 °C and operated in TEABF4/acetonitrile organic electrolyte show a specific capacitance of 23.13 F g-1 at 5 mA cm-2 and enhanced capacitance retention at 3.2 V, which well exceeds the normal working voltage of a commercial EDLC product (2.7 V). This work delivers an additional feasible approach of using ZnO ALD modification of AC materials, enhancing and promoting stable EDLC cells under high working voltages. show less
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Abstract
Electron transfer (ET) across proteins is ubiquitous in nature, such as the notable photosynthesis example, where light-induced charge separation takes place within the reaction center, followed by sequential ET via intramolecular cofactors within the protein. Here, we introduce carbon dots (C-Dots), which are slowly gaining momentum in being game changers for next …show moreElectron transfer (ET) across proteins is ubiquitous in nature, such as the notable photosynthesis example, where light-induced charge separation takes place within the reaction center, followed by sequential ET via intramolecular cofactors within the protein. Here, we introduce carbon dots (C-Dots), which are slowly gaining momentum in being game changers for next generation advanced technology platforms, as valuable ET dopants of proteins. We report on a heterostructure configuration, comprised of a C-Dot and a tethered hemin molecule, showing appealing electron/hole donor-acceptor properties. We show by transient absorption and emission spectroscopies that rapid intramolecular charge separation is happening following light excitation, which can be ascribed to an ultrafast ET and hole transfer (HT) between the C-Dot donor to the hemin acceptor. Upon integrating the heterostructure into protein biopolymers, we show that this ET/HT within the heterostructure configuration is 3.3 times faster compared to the same process in solution, indicating the active role of the protein in supporting the rapid light-induced long range intermolecular charge separation. We further use impedance, electrochemical, and transient photocurrent measurements to show that the light induced transient charge separation results in enhanced ET and HT efficiency across the protein biopolymer. The charge conduction across our protein biopolymers, reaching nearly 0.01 S∙cm-1, along with the simplicity of their formation and their low-cost promote their use in a variety of optoelectronic devices, such as artificial photosynthesis, photo-responsive protonic-electronic transistors, and photodetector. show less
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Abstract
Long-term stability is a key requirement for anion-exchange membranes (AEMs) for alkaline fuel cells and electrolyzers that is yet to be fulfilled. Different cationic chemistries are being exploited to reach such a goal, and metallopolymers present the unique advantage of chemical stability towards strong nucleophiles as compared to organic cations. Yet, the few …show moreLong-term stability is a key requirement for anion-exchange membranes (AEMs) for alkaline fuel cells and electrolyzers that is yet to be fulfilled. Different cationic chemistries are being exploited to reach such a goal, and metallopolymers present the unique advantage of chemical stability towards strong nucleophiles as compared to organic cations. Yet, the few metallopolymers tested in strongly alkaline conditions or even in fuel cells still degrade. Therefore, fundamental studies can be advantageous in directing future developments towards this goal. Here, a systematic study of the effect of ligand valency is presented, using nickel-based metallopolymers on polynorbornene backbones, functionalized with multidentate pyridine ligands. Metallopolymers using a single ligand type as well as all the possible mixtures are prepared and their relative stability towards aggressive alkaline conditions compared. Metallopolymer in which nickel ions are hexacoordinated with two tridentate ligands demonstrates superior stability. More importantly, by comparing all the metallopolymers' stability, the reason behind such relative stability provides design parameters for novel metallopolymer AEMs. show less
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Abstract
The use of photosystem II (PSII) in hybrid bio-photoelectrochemical cells for conversion of solar energy to electrical current is hampered by PSII's narrow absorption cross-section and the generally poor electrical connection between isolated complex and different anode materials. Here, we merge isolated market-grade spinach PSII with 25 nm cystamine-2,6-dichlorobenzoquinone …show moreThe use of photosystem II (PSII) in hybrid bio-photoelectrochemical cells for conversion of solar energy to electrical current is hampered by PSII's narrow absorption cross-section and the generally poor electrical connection between isolated complex and different anode materials. Here, we merge isolated market-grade spinach PSII with 25 nm cystamine-2,6-dichlorobenzoquinone (cys-DCBQ) modified Au-nanoparticles (PSII–AuNPCys-DCBQ) to obtain one of the highest reported photocurrent values to date (35 mA cm-2 mg-1 chlorophyll), retaining the native oxygen evolution properties of PSII. More than 80% of the PSII in solution assembles stably onto the AuNPCys-DCBQ. Spectroscopic studies show strong functional association in these hybrid particles. Mechanistic investigations reveal a dual role of the quinone-modified AuNPs, harvesting and transference of the excitation energy to PSII (resulting in ∼10-fold enhancement of anodic photocurrent in the 500–550 nm irradiation range) and simultaneously improving the electron transfer from PSII into the graphite anode (by almost 6-fold over the entire visible range of light). show less
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Abstract
We report in this study on the combination of resonance frequency shift measurements with the use of Electrochemical Quartz Crystal Microbalance (EQCM), alongside in-situ electrochemical surface stress (ESS) analysis, which provides a comprehensive description of both the microscopic and macroscopic processes occurring on the surface of the oxygen reduction …show moreWe report in this study on the combination of resonance frequency shift measurements with the use of Electrochemical Quartz Crystal Microbalance (EQCM), alongside in-situ electrochemical surface stress (ESS) analysis, which provides a comprehensive description of both the microscopic and macroscopic processes occurring on the surface of the oxygen reduction reaction (ORR) electrocatalyst. The resonance frequency shift was measured on an Au/MnOx electrode in both de-oxygenated and O2 saturated electrolytes. The results obtained with the use of frequency shift measurements (with the use of EQCM) are in good agreement with the interpretations of the data originated from the surface stress response. It was found that the structural changes identified by the surface stress led to the insertion and release of water molecules into and out of the manganese-oxide film. These findings are used to explain the mechanical failure of the electrocatalyst film subsequent to multiple charge/discharge cycles, hence revealing an additional valuable information on the poor mechanical stability of the manganese-oxide film. Moreover, the presence of oxygen in the electrolyte resulted in mass changes, being qualitatively similar to those recorded in de-oxygenated electrolyte, albeit with different intensities during the ORR, further validating the proposed catalytic mechanism. show less
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Abstract
Since effective thermal insulation of buildings could significantly decrease energy consumption worldwide, this study examined the potential of concrete tiles with complex geometries at improving thermal performance in building envelopes. The study focused on air flow characteristics that occur near the external surface of the tile, and their influence on the rate of …show moreSince effective thermal insulation of buildings could significantly decrease energy consumption worldwide, this study examined the potential of concrete tiles with complex geometries at improving thermal performance in building envelopes. The study focused on air flow characteristics that occur near the external surface of the tile, and their influence on the rate of heat transfer within the material. Six groups of sculptured tiles were developed, using a systematic approach (i.e., repetition of basic geometries), biomimicry, and inspiration from natural envelopes. Air flow behavior and heat transfer rates were examined at three different wind speeds, through both experiments and computational fluid dynamics simulations using a configuration of flow impingement that can be regarded as the worst case scenario. After successfully validating the data, additional numerical simulations were conducted for all developed tiles using the Star-CCM + commercial software. The results showed an improvement in the insulation performance of about half of all the tested cases. Moreover, significant improvements were seen in the geometries that mimicked animal fur, achieving heat transfer rates that were up to 24% lower than those achieved by smooth tiles. Our results indicate that the application of such tiles with increased thermal resistance could save on thermal insulation materials and improve the thermal performance of building facades. show less
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Abstract
Metal–support interactions have a strong and pivotal influence on catalyst properties. In many cases, these interactions can direct reaction activity, stability, and selectivity. Hence, controlling such interactions has high potential for enhancing catalytic performance. One approach to controlling metal–support interactions is to use a surface phase oxide, wherein a …show moreMetal–support interactions have a strong and pivotal influence on catalyst properties. In many cases, these interactions can direct reaction activity, stability, and selectivity. Hence, controlling such interactions has high potential for enhancing catalytic performance. One approach to controlling metal–support interactions is to use a surface phase oxide, wherein a thin layer of a metal oxide is deposited on the surface of an underlying support material to form a hierarchical structure. The addition of a surface phase oxide, as an intermediate between the metal and the underlying support, offers greater possibilities for controlling the metal support interactions by tuning the composition and architecture of both support components. In this review, we discuss current knowledge of surface phase oxides from both experimental and computational points of view. Specifically, we discuss their surface and chemical properties, their effect on supported metal particles, and their catalytic performance. We compare surface phase oxides with other architectures, such as bulk oxides and supported metal oxide particles, and describe cases in which this hierarchical configuration has been applied to significantly enhance catalytic reforming, hydrogenation, and hydrogenolysis reactions. Finally, we highlight aspects that warrant future research and review opportunities for tailoring the performance of next-generation supported metal catalysts. show less
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Abstract
Non-polluting fuels, such as hydrogen, are widely considered to be a promising way to decrease the environmental problems caused by the burning of fossil fuels. Finding materials that can help us to generate these “clean” fuels is a difficult and time-consuming process. Computer simulation technology is the most important tool in this area, because it helps scientists …show moreNon-polluting fuels, such as hydrogen, are widely considered to be a promising way to decrease the environmental problems caused by the burning of fossil fuels. Finding materials that can help us to generate these “clean” fuels is a difficult and time-consuming process. Computer simulation technology is the most important tool in this area, because it helps scientists to understand existing materials and can also help them to design new types of materials. In this article, we explain how certain materials can help us to produce hydrogen, a clean fuel, from water, and we also describe how computer simulation technology can offer a route for the discovery of new efficient materials. show less
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Abstract
In recent decades, polymer electrolyte membrane fuel cell (PEMFC) technologies have attracted research attention as promising candidates for next-generation energy conversion systems. This work deals with the effect of operating conditions and the construction of a typical model for PEMFCs, using electrochemical impedance spectroscopy (EIS) and distribution of relaxation …show moreIn recent decades, polymer electrolyte membrane fuel cell (PEMFC) technologies have attracted research attention as promising candidates for next-generation energy conversion systems. This work deals with the effect of operating conditions and the construction of a typical model for PEMFCs, using electrochemical impedance spectroscopy (EIS) and distribution of relaxation times analysis. In operando EIS measurements were carried out on PEMFCs under different operating conditions. The measurements were analyzed using a genetic algorithm to obtain the distribution function of relaxation times (DFRT) models as analytical functions. The obtained model consists of four peak functions that fit the four main physical processes known to occur within the fuel cell during operation: proton conduction within the membrane, proton conduction within the catalyst layer (CL), oxygen reduction reaction’s charge transfer, and oxygen mass transfer within the CL and the gas diffusion layer. In addition, this method enabled examining each physical process’s response to operating conditions (such as temperature, humidity, and output current) and quantifying each process’s effective resistance. In particular, we were able to quantify the resistance to proton conduction within the CL, a process known to have a low contribution to the overall impedance, hence many times eclipsed by other processes. The resulting model can be further used in, for example, PEMFC degradation research, owing again to the fact that the model’s analytical form is stable while its parameters change as the cell degrades. show less
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Abstract
Identifying key catalyst parameters that govern catalytic performance is a main challenge for many reactions. The complex and convoluted behavior of the Mn2O3-Na2WO4/SiO2 catalyst for the oxidative coupling of methane (OCM) makes this task even more challenging. Herein, structure–function correlations are obtained …show moreIdentifying key catalyst parameters that govern catalytic performance is a main challenge for many reactions. The complex and convoluted behavior of the Mn2O3-Na2WO4/SiO2 catalyst for the oxidative coupling of methane (OCM) makes this task even more challenging. Herein, structure–function correlations are obtained using a simplified methodology that involves cross-referencing statistically estimated reaction kinetic parameters with various experimentally measured catalyst and reaction properties. These correlations and conclusions are shown to be consistent with literature data, which was obtained using advanced in situ techniques. Specifically, these correlations highlight the importance of maintaining highly dispersed Mn2O3 particles in a dispersed Na2WO4 melt, under OCM conditions. The promotion of OCM is associated with the efficient interaction of the two phases in the gel-like formation, which apparently promotes the release of the catalytic active species. However, it is also shown that under reaction conditions the molten state of the Na2WO4 promotes the growth of a separate Mn2O3 phase, which enhances CO2 formation over the OCM by reducing the effective level of interaction between the Mn and the W phases. As a whole, this work not only provides new data but also exemplifies a relatively simple and general tool for identifying catalyst descriptors that govern reaction performance. show less
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Abstract
Platinum group metal (PGM)‐free catalysts for oxygen reduction reaction have shown high oxygen reduction reaction activity in alkaline media. In order to further increase the power density of anion‐exchange membrane fuel cells (AEMFCs), PGM‐free catalysts need to have a high site density to reach high current densities. Herein, synthesis, characterization, and utilization …show morePlatinum group metal (PGM)‐free catalysts for oxygen reduction reaction have shown high oxygen reduction reaction activity in alkaline media. In order to further increase the power density of anion‐exchange membrane fuel cells (AEMFCs), PGM‐free catalysts need to have a high site density to reach high current densities. Herein, synthesis, characterization, and utilization of heat‐treated iron porphyrin aerogels are reported as cathode catalysts in AEMFCs. The heat treatment effect is thoroughly studied and characterized using several techniques, and the best performing aerogel is studied in AEMFC, showing excellent performance, reaching a peak power density of 580 mW cm−2 and a limiting current density of as high as 2.0 A cm−2, which can be considered the state‐of‐the‐art for PGM‐free based AEMFCs.
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Alon Z Shapira,
Nir Gavish,
Hannes Uecker,
Arik Yochelis
Abstract
Optimizing the properties of the mosaic morphology of bulk heterojunction (BHJ) organic photovoltaics (OPV) is not only challenging technologically but also intriguing from the mechanistic point of view. Among the recent breakthroughs in studies of BHJ morphology, is the identification and utilization of a three-phase (donor/mixed/acceptor) BHJ, where the (intermediate) …show moreOptimizing the properties of the mosaic morphology of bulk heterojunction (BHJ) organic photovoltaics (OPV) is not only challenging technologically but also intriguing from the mechanistic point of view. Among the recent breakthroughs in studies of BHJ morphology, is the identification and utilization of a three-phase (donor/mixed/acceptor) BHJ, where the (intermediate) mixed-phase can inhibit morphological changes, such as phase separation. Using a continuum approach, we develop and analyze a model that undertakes the coupling between the spatiotemporal evolution of the material and charge dynamics along with charge transfer at the device electrodes. Starting from an ideal BHJ represented by stripes, we reveal and distinguish between generic mechanisms that alter the evolution of stripes: the bending (zigzag mode) and the pinching (cross-roll mode) of the donor/acceptor domains. We then emphasize that the latter instability mode, is notorious as it leads to the formation of disconnected domains and hence to loss of charge flux. Consequently, the analysis implies that donor-acceptor mixtures with higher mixing energy are more likely to develop pinching under charge-flux boundary conditions. We believe that these results provide a qualitative roadmap for morphological BHJ optimization, using mixed-phase composition and moreover, open new vistas to application involving three phase morphologies, such as ion-intercalated rechargeable batteries. show less
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Abstract
We report on an intriguing aspect of the effects of microstructure and chemistry on thermoelectric (TE) transport properties of nanostructured Bi2Te3-based compounds that are associated with their topologically insulating (TI) nature. Nanograined n-type Bi2Te3 and Bi1.94Nd0.06Te3 samples were …show moreWe report on an intriguing aspect of the effects of microstructure and chemistry on thermoelectric (TE) transport properties of nanostructured Bi2Te3-based compounds that are associated with their topologically insulating (TI) nature. Nanograined n-type Bi2Te3 and Bi1.94Nd0.06Te3 samples were consolidated by uniaxial hot pressing of nanoparticles (NPs) produced by solution synthesis. The grain size was controlled by changing the duration of the hot-pressing process. We found that the room-temperature values of electrical conductivity, Seebeck coefficient, and charge carrier mobility of the consolidated Bi2Te3 samples increase with the reduction of the average grain size. This phenomenon was observed earlier for Bi2Se3, which is a well-known TI material. We also found that Nd-doping reduces the electrical conductivity, Seebeck coefficient, charge carrier mobility, and thermal conductivity near room temperature (310 K). Interestingly, Nd-doping reverses the dependence of mobility on grain size compared to undoped Bi2Te3, which is associated with its magnetic moment. These observations can be utilized for further enhancement of the TE power factor of bulk nanograined TE materials to be applied for power generation near room temperature as well as cooling, in addition to the positive effect on reducing thermal conductivity due to phonon scattering. show less
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Abstract
Carbon nanotubes (CNTs) are stiff, all-carbon macromolecules with diameters as small as one nanometer and few microns long. Solutions of CNTs in chlorosulfonic acid (CSA) follow the phase behavior of rigid rod polymers interacting via a repulsive potential and display a liquid crystalline phase at sufficiently high concentration. Here, we show that small-angle X-ray …show moreCarbon nanotubes (CNTs) are stiff, all-carbon macromolecules with diameters as small as one nanometer and few microns long. Solutions of CNTs in chlorosulfonic acid (CSA) follow the phase behavior of rigid rod polymers interacting via a repulsive potential and display a liquid crystalline phase at sufficiently high concentration. Here, we show that small-angle X-ray scattering and polarized light microscopy data can be combined to characterize quantitatively the morphology of liquid crystalline phases formed in CNT solutions at concentrations from 3 to 6.5% by volume. We find that upon increasing their concentration, CNTs self-assemble into a liquid crystalline phase with a pleated texture and with a large inter-particle spacing that could be indicative of a transition to higher-order liquid crystalline phases. We explain how thermal undulations of CNTs can enhance their electrostatic repulsion and increase their effective diameter by an order of magnitude. By calculating the critical concentration, where the mean amplitude of undulation of an unconstrained rod becomes comparable to the rod spacing, we find that thermal undulations start to affect steric forces at concentrations as low as the isotropic cloud point in CNT solutions. show less
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Abstract
This paper presents an ultrasonic method for tracking the decomposition front in ablating silica-phenolic thermal protection system material. The method exploits diffuse ultrasonic backscatter from the material microstructure to account for the temperature-dependent change of the speed of sound. The method is demonstrated in a series of ablation tests performed at a …show moreThis paper presents an ultrasonic method for tracking the decomposition front in ablating silica-phenolic thermal protection system material. The method exploits diffuse ultrasonic backscatter from the material microstructure to account for the temperature-dependent change of the speed of sound. The method is demonstrated in a series of ablation tests performed at a heat flux of 1350 W/cm2 provided by an oxy-acetylene torch. Validation of the method is performed using machining, ultrasound, and micro–computed tomography scanning of the ablated samples. The measurement error in all tests does not exceed 1 mm. Analysis of the data suggests that, during the active ablation phase, temperature rise in the virgin material zone is low and the speed of sound correction is not required, whereas the main advantage of the method comes during the heat soak-back phase. Performed thermo-acoustic characterization of silica phenolic shows a linear dependence between the speed of sound and temperature up to 210°C. This finding opens a way to use the backscatter for estimation of temperature distribution in the virgin material. Finally, the study presents the measurement of acoustic attenuation to provide a reference for the application of the method to additional thermal protection materials, except silica phenolic. show less
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Abstract
Porous carbon materials attract great interest in a wide range of applications such as batteries, fuel cells, and membranes, due to their large surface area, structural and compositional tunability, and chemical stability. While micropores are typically obtained when preparing carbon materials by pyrolysis, the fabrication of mesoporous, and especially macroporous …show morePorous carbon materials attract great interest in a wide range of applications such as batteries, fuel cells, and membranes, due to their large surface area, structural and compositional tunability, and chemical stability. While micropores are typically obtained when preparing carbon materials by pyrolysis, the fabrication of mesoporous, and especially macroporous carbons is more challenging, yet important for enhancing mass transport. Herein, template-free regular macroporous carbons are prepared from a mixture of unfolded (linear) and folded (single-chain nanoparticles, SCNP) polyvinylpyrrolidone chains. While having the same chemical composition, the different molecular architectures lead to phase separation even before pyrolysis, creating a dense cell architecture, which is retained upon carbonization. Upon increasing the SCNP content, the homogeneity of the pore network increases and the specific surface area is enlarged 3-5-fold, until ideal properties are obtained at 75% SCNP, as observed by high-resolution scanning electron microscopy and N2 physisorption porosimetry. The materials are further investigated as hydrazine oxidation electrocatalysts, demonstrating the link between the evolving morphology and current density. Importantly, this study demonstrates the role of polymer architecture in macroporosity templating in carbon materials, providing a new approach to develop complex carbon architectures without the need for external templating. show less
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Abstract
Single and multirotor drones are increasingly used for commercial and humanitarian applications, including product delivery [1], disaster relief [2], wildlife tracking [3], agriculture [4], andlab-on-a-drone functions [5]. Their main advantages include vertical takeoff and landing (VTOL) capability, hovering, and autonomous flight over difficult [6] and complex terrains …show moreSingle and multirotor drones are increasingly used for commercial and humanitarian applications, including product delivery [1], disaster relief [2], wildlife tracking [3], agriculture [4], andlab-on-a-drone functions [5]. Their main advantages include vertical takeoff and landing (VTOL) capability, hovering, and autonomous flight over difficult [6] and complex terrains [7]. Despite their ubiquitous deployment, they carry lighter payloads and have lower endurance than conventional fixed-wing aircraft. This problem is exacerbated in the case of battery-powered drones that have a particularly short flight time. show less
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Dmitry Baimel,
Nilanjan Roy Chowdhury,
Juri Belikov,
Yoash Levron
Abstract
The paper presents a new active diode bridge fault current limiter (FCL) topology, and compares it to the classic diode bridge, Series Dynamic Breaking Resistor (SDBR), and active diode bridge FCL circuits. The comparison is done using a benchmark system that includes a 9 MW wind turbine with a doubly fed induction generator (DFIG), two 50 MW synchronous generators, and …show moreThe paper presents a new active diode bridge fault current limiter (FCL) topology, and compares it to the classic diode bridge, Series Dynamic Breaking Resistor (SDBR), and active diode bridge FCL circuits. The comparison is done using a benchmark system that includes a 9 MW wind turbine with a doubly fed induction generator (DFIG), two 50 MW synchronous generators, and three step-up transformers. The results show that all three FCLs improve transient stability by limiting the currents peak, terminal voltage drop, active and reactive powers, and torque transients. show less
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Abstract
We report an ultra long range energy transfer in a layered donor:spacer:acceptor structures, which consist of the typical organic photovoltaic material system of P3HT as the donor and PCBM as the acceptor. By varying the thicknesses of spacer and acceptor layers we show that the energy transfer is to the full volume of the acceptor and not just to its nearest interface …show moreWe report an ultra long range energy transfer in a layered donor:spacer:acceptor structures, which consist of the typical organic photovoltaic material system of P3HT as the donor and PCBM as the acceptor. By varying the thicknesses of spacer and acceptor layers we show that the energy transfer is to the full volume of the acceptor and not just to its nearest interface, and we find an effective energy transfer range on the order of about 100nm. Our efforts to elucidate the origin of this process, both theoretically and experimentally, are discussed as well. Although it was recently implied that an exceptionally large energy transfer may take place in this material system, this is the first time, to the best of our knowledge, that the energy transfer mechanism is characterized in a quantitative way and compared to the common models. Our analysis offers new prospects for the familiar photovoltaic bi-layer configurations, which may be very efficient if the ultra long range energy transfer is utilized through a suitable architecture. show less
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Daniel A Grave,
David S Ellis,
Yifat Piekner,
Moritz Kölbach,
Hen Dotan,
Asaf Kay,
Patrick Schnell,
Roel van de Krol,
Fatwa F Abdi,
Dennis Friedrich,
Avner Rothschild
Abstract
Light absorption in strongly correlated electron materials can excite electrons and holes into a variety of different states. Some of these excitations yield mobile charge carriers, whereas others result in localized states that cannot contribute to photocurrent. The photogeneration yield spectrum, ξ(λ), represents the wavelength-dependent ratio between the contributing …show moreLight absorption in strongly correlated electron materials can excite electrons and holes into a variety of different states. Some of these excitations yield mobile charge carriers, whereas others result in localized states that cannot contribute to photocurrent. The photogeneration yield spectrum, ξ(λ), represents the wavelength-dependent ratio between the contributing absorption that ultimately generates mobile charge carriers and the overall absorption. Despite being a vital material property, it is not trivial to characterize. Here, we present an empirical method to extract ξ(λ) through optical and external quantum efficiency measurements of ultrathin films. We applied this method to haematite photoanodes for water photo-oxidation, and observed that it is self-consistent for different illumination conditions and applied potentials. We found agreement between the extracted ξ(λ) spectrum and the photoconductivity spectrum measured by time-resolved microwave conductivity. These measurements revealed that mobile charge carrier generation increases with increasing energy across haematite’s absorption spectrum. Low-energy non-contributing absorption fundamentally limits the photoconversion efficiency of haematite photoanodes and provides an upper limit to the achievable photocurrent that is substantially lower than that predicted based solely on absorption above the bandgap. We extended our analysis to TiO2 and BiVO4 photoanodes, demonstrating the broader utility of the method for determining ξ(λ). Although the photogeneration yield spectrum is a key property for photoabsorbers in photovoltaic and photoelectrochemical cells, its characterization remains challenging. An empirical method to extract this parameter through quantum efficiency measurements of ultrathin films is proposed. show less
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Abstract
Modern applications require high energy density lithium-ion batteries (LIBs), inciting the search for high capacity anode materials. Recently, Aluminum (Al) anodes have reemerged as Li-alloyed anode material, but so far have not presented sufficient performance with commercially acceptable mass loadings. Interestingly, the active material intrinsic conductivity is not …show moreModern applications require high energy density lithium-ion batteries (LIBs), inciting the search for high capacity anode materials. Recently, Aluminum (Al) anodes have reemerged as Li-alloyed anode material, but so far have not presented sufficient performance with commercially acceptable mass loadings. Interestingly, the active material intrinsic conductivity is not fully exploited in the design of Al anodes, as traditional powder-based electrodes still rely on carbonaceous additives to improve the conductivity. Herein, we provide a proof-of-principle for the design of a binary carbon-free Al/binder electrode, targeting high areal capacities for the powder-based anode with increased active material content. The simple binary electrode concept has been proven feasible as anodes, producing reversible capacities of about 3 mAh cm−2, higher than many similar carbon-based systems. By eliminating the conductive additives, the electrode advantaged from high active material loading, and from the mitigation of surface-related side reactions. The binary system behavior was more stable in prolonged cycling, demonstrating that any beneficial role of the carbon in maintaining the electrical conductivity and diminishing Al pulverization is only temporary. The insights on the high loading Al/binder anode provide first guidelines for future high-energy density LIBs via implementation of state-of-the-art architectures in binary Al-based anodes. show less
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Abstract
The reforming-controlled compression ignition (RefCCI) is an innovative concept integrating the benefits of the low-temperature combustion engine and the High-Pressure Thermochemical Recuperation. This combination enables achieving high thermal efficiency in a wide operating range while mitigating pollutant emissions. This work reports for the first time on results of …show moreThe reforming-controlled compression ignition (RefCCI) is an innovative concept integrating the benefits of the low-temperature combustion engine and the High-Pressure Thermochemical Recuperation. This combination enables achieving high thermal efficiency in a wide operating range while mitigating pollutant emissions. This work reports for the first time on results of the RefCCI concept experimental prove and investigation. The experiment findings confirm the results of the previous numerical studies. In addition, new important knowledge was gained on engine performance and emissions dependence on the injection timing of the primary and reformate fuels, as well as on the fuel mixture reactivity. The results show the thermal efficiency improvement by 4–9% (relative) compared to the same engine operation in diesel mode. In the RefCCI mode, the CO emission is lowered with the increase of load, contrary to the trend in the diesel mode. As expected, NOx and total particle number emissions are significantly lower than with the diesel counterpart. The emission of nucleation mode particles is fairly similar to diesel, but the number of accumulation mode particles is reduced by the order of magnitude. show less
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David Becker-Koch,
Miguel Albaladejo-Siguan,
Yvonne J Hofstetter,
Olga Solomeshch,
Darius Pohl,
Bernd Rellinghaus,
Nir Tessler,
Yana Vaynzof
Abstract
The efficiency of PbS quantum dot (QD) solar cells has significantly increased in recent years, strengthening their potential for industrial applications. The vast majority of state-of-the-art devices utilize 1,2-ethanedithiol (EDT)-coated PbS QD hole extraction layers, which lead to high initial performance, but result in poor device stability. While excellent performance …show moreThe efficiency of PbS quantum dot (QD) solar cells has significantly increased in recent years, strengthening their potential for industrial applications. The vast majority of state-of-the-art devices utilize 1,2-ethanedithiol (EDT)-coated PbS QD hole extraction layers, which lead to high initial performance, but result in poor device stability. While excellent performance has also been demonstrated with organic extraction layers, these devices include a molybdenum trioxide (MoO3) layer, which is also known to decrease device stability. Herein, we demonstrate that organic layers based on a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) polymer doped with C60F48 can serve as hole extraction layers for efficient EDT-free and MoO3-free QD solar cells. Such layers are shown to offer high conductivity for facile hole transport to the anode, while effectively blocking electrons due to their low electron affinity. We show that our approach is versatile and is applicable also to AgBiS2 QD solar cells. show less
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Abstract
Hybrid halide perovskites (HHPs) exhibit exceptional photoelectric properties, facilitating highly efficient modern solar cells and photoconductive technologies. Both ion migration and intrinsic spontaneous polarization have been proposed as the main source of enhanced photoelectric activity, but the exact origin of the advantageous properties has remained elusive. Here …show moreHybrid halide perovskites (HHPs) exhibit exceptional photoelectric properties, facilitating highly efficient modern solar cells and photoconductive technologies. Both ion migration and intrinsic spontaneous polarization have been proposed as the main source of enhanced photoelectric activity, but the exact origin of the advantageous properties has remained elusive. Here, we combined nanoscale and macroscale device characterization studies to demonstrate that intrinsic polarization conductivity governs photoconductivity in HHP films. Conductive atomic force microscopy under variable light and temperature conditions showed that the photocurrent in these materials is directional and flows along the long crystallographic axis, as opposed to other conduction mechanisms that prioritize the shortest path between the electrode and the conductive tip. It was also shown that the photocurrent is suppressed at the tetragonal-to-cubic transformation. The findings were confirmed by macroscale device measurements. Following the nonvolatile memory nature of polarization domains, photoconductive memristive behavior was demonstrated. Understanding the origin of photoelectric activity in HHPs allows designing devices with enhanced functionality. show less
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Abstract
Power and efficiency characteristics of a hybrid cycle combining an electrochemical device (Fuel-Cell) and an internal combustion engine (ICE) were analyzed using the low-dissipation model. The low-dissipation model links energy dissipation with the energy transfer rate through the cycle. In the considered cycle, the electrochemical device transforms chemical potential …show morePower and efficiency characteristics of a hybrid cycle combining an electrochemical device (Fuel-Cell) and an internal combustion engine (ICE) were analyzed using the low-dissipation model. The low-dissipation model links energy dissipation with the energy transfer rate through the cycle. In the considered cycle, the electrochemical device transforms chemical potential of the fuel to electrical work, and the ICE uses the heat rejected by the electrochemical device and its exhaust effluent for mechanical work production. The cycle efficiency was calculated as a function of the hybridization level. The latter is defined as the electrical work fraction in the total cycle work. The results of the study show that the cycle efficiency is growing with the electrical work fraction increase. On the other hand, maximum power of the cycle is attained at an intermediate hybridization level. Moreover, power to weight ratio and power density of the cycle have maxima at different hybridization level. Cycle cooling losses are modeled as heat leak to the ambient that depends on the temperature and the duration of the cycle. Cooling losses are found to be the most influential parameter in optimization of the hybridization level for maximum power. In the extreme case of zero cooling losses, maximum power could be attained with ICE operation alone without the electrochemical reaction. The latter finding might be of interest for aerial propulsion systems. However, if efficiency is more important - for example for ground propulsion systems - the hybrid cycle is beneficial. show less
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Abstract
As a conventional electrode material of electric double-layer capacitors (EDLC), activated carbon (AC) still faces challenges to exhibit high capacitance. To address this problem, herein, we introduce a combined method of oxygen plasma and Al2O3 tomic layer deposition (ALD) on AC electrodes to reduce the impedance and improve the cycle stability …show moreAs a conventional electrode material of electric double-layer capacitors (EDLC), activated carbon (AC) still faces challenges to exhibit high capacitance. To address this problem, herein, we introduce a combined method of oxygen plasma and Al2O3 tomic layer deposition (ALD) on AC electrodes to reduce the impedance and improve the cycle stability of EDLC. The defect structure can be precisely designed by simply tuning the oxygen-plasma treatment time, thereby affecting the microstructures of AC electrode. Such a tactic permits the first-operated AC electrode with more defects and the ALD passivation of AC resulting in an outstanding rate performance for the device (40.6 F g–1 at 5 mA cm–2, 20.1 Fg–1 at 100 mA cm–2) and cycling stability (∼90% retention after 5,000 cycles). This benefit from the synergistic effect of defects from doped oxygen and stable aluminum oxide layer on the electrode surface. This work delivers a feasible strategy to construct a stable AC material with superior cycling performance for supercapacitor. show less
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Abstract
In the field of power system dynamics, a main challenge is to properly tune the inverter control parameters, where one important parameter is the inverter's output impedance, physical or virtual. In this work, we provide a proof showing that a minimal output impedance must be used in order to keep the system stable. Although this result is well-known among practicing …show moreIn the field of power system dynamics, a main challenge is to properly tune the inverter control parameters, where one important parameter is the inverter's output impedance, physical or virtual. In this work, we provide a proof showing that a minimal output impedance must be used in order to keep the system stable. Although this result is well-known among practicing engineers, our proof reveals a fundamental property which causes instabililty, namely the pole excess of the inverter dynamic model. To prove this claim we model the system as a signal flow diagram, where the output impedances of the inverters are described using static gain feedback. Based on this model, we show that the typical dynamic model of grid supporting inverters has a pole excess larger than 2, which causes instability when high feedback gain is used. This result may be used to design a numerical method for estimating the minimal impedance. The theorem is validated based on an array of photovoltaic plants in the Ramat Negev region, which is part of the Israeli power grid. show less
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Abstract
The latest progress in alkaline anion-exchange membranes has led to the expectation that less costly catalysts than those of the platinum-group metals may be used in anion-exchange membrane fuel cell devices. In this work, we compare structural properties and the catalytic activity for the hydrogen-oxidation reaction (HOR) for carbon-supported nanoparticles of Ni …show moreThe latest progress in alkaline anion-exchange membranes has led to the expectation that less costly catalysts than those of the platinum-group metals may be used in anion-exchange membrane fuel cell devices. In this work, we compare structural properties and the catalytic activity for the hydrogen-oxidation reaction (HOR) for carbon-supported nanoparticles of Ni, Ni3Co, Ni3Cu, and Ni3Fe, synthesized by chemical and solvothermal reduction of metal precursors. The catalysts are well dispersed on the carbon support, with particle diameter in the order of 10 nm, and covered by a layer of oxides and hydroxides. The activity for the HOR was assessed by voltammetry in hydrogen-saturated aqueous solutions of 0.1 mol dm-1 KOH. A substantial activation by potential cycling of the pristine catalysts synthesized by solvothermal reduction is necessary before these become active for the HOR; in situ Raman spectroscopy shows that after activation the surface of the Ni/C, Ni3Fe, and Ni3Co catalysts is fully reduced at 0 V, whereas the surface of the Ni3Cu catalyst is not. The activation procedure had a smaller but negative impact on the catalysts synthesized by chemical reduction. After activation, the exchange-current densities normalized with respect to the ECSA (electrochemically active surface area) were approximately independent of composition but relatively high compared to catalysts of larger particle diameter. show less
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Qingzhi An,
Fabian Paulus,
David Becker-Koch,
Changsoon Cho,
Qing Sun,
Andreas Weu,
Sapir Bitton,
Nir Tessler,
Yana Vaynzof
Abstract
Non-radiative recombination in the perovskite bulk and at its interfaces prohibits the photovoltaic performance from reaching the Shockley-Queisser limit. While interfacial recombination has been widely discussed and demonstrated, bulk recombination and especially the influence of grain boundaries remain under debate. Most studies explore the role of grain boundaries …show moreNon-radiative recombination in the perovskite bulk and at its interfaces prohibits the photovoltaic performance from reaching the Shockley-Queisser limit. While interfacial recombination has been widely discussed and demonstrated, bulk recombination and especially the influence of grain boundaries remain under debate. Most studies explore the role of grain boundaries on perovskite films rather than devices, making it difficult to link the film properties with those of the devices. Here, we systematically investigate the effects of grain boundaries on the performance of perovskite solar cells by two different methods. By combining experimental characterization with theoretical device simulations, we find that the recombination at grain boundaries is diffusion limited and hence is inversely proportional to the grain area to the power of 3/2. Consequently, the prevalence of small grains—which act as recombination hot spots—across the perovskite active layer dictates the photovoltaic performance of the perovskite solar cells. show less
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Abstract
MgSc2Se4 is a promising magnesium-ion solid electrolyte possessing a high room temperature Mg+2 conductivity (~ 10−4 S/cm). MgSc2Se4 also has demonstrated considerably high electronic conductivity (10−5÷10−8 S/cm). Such high electronic conductivity substantially restricts the applications of …show moreMgSc2Se4 is a promising magnesium-ion solid electrolyte possessing a high room temperature Mg+2 conductivity (~ 10−4 S/cm). MgSc2Se4 also has demonstrated considerably high electronic conductivity (10−5÷10−8 S/cm). Such high electronic conductivity substantially restricts the applications of the material in all solid-state Mg-ion batteries. The efforts to lower the electronic conductivity include the enrichment of the material with selenium aliovalent doping, albeit without any tangible success. This suggests that the electronic conductivity may follow a model, which is different from a common model of charge transfer by electrons in a conduction band of the wide band gap semiconductor MgSc2Se4. Here, we provide an evidence that the electronic transport in the Mg-Sc-Se ceramic is facilitated via the Berthelot-type conductivity mechanism, suggesting an electronic transport through a low-conducting matrix stuffed with nano-scaled free electron-containing regions. These inclusions are well-distributed across the Mg-Sc-Se, and the electronic transport takes place via electron tunneling between these conductive regions, through low-conducting matrix spacers. It is shown that these conductive zones comprised of elemental metallic Sc and ScSe mix being a metallic-type electronic conductor. The nature of these conductive inclusions and the synthetic parameters controlling the appearance of such conductive areas are discussed, as well as routes to mitigate their formation. show less
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Abstract
In recent years power quality monitoring tools are becoming a necessity, and many studies focus on detection and classification of Power Quality Disturbances (PQD)s. However, presently a core obstacle that prevents the direct comparison of such classification techniques is the lack of a standard database that can be used as a benchmark. In this light, we propose here …show moreIn recent years power quality monitoring tools are becoming a necessity, and many studies focus on detection and classification of Power Quality Disturbances (PQD)s. However, presently a core obstacle that prevents the direct comparison of such classification techniques is the lack of a standard database that can be used as a benchmark. In this light, we propose here an open-source software which enables the creation of synthetic power quality disturbances, and is designed specifically for comparison of PQD classifiers. The software produces several types of standard disturbances from the literature, with varying repetitions and random parameters of the labeled disturbances, and includes two reference classifiers that are based on deep-learning techniques. Due to the good performance of these classifiers, we suggest that they can be used by the community as benchmarks for the development of new and better PQD classification algorithms. The developed code is available online, and is free to use. show less
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Abstract
Coating of filtration membranes with a polymer brush holds great promise for efficiently preventing the deposition of fouling particles. The polymer chains are compressed by incoming particles, carried with the permeation flow towards the membrane, and consequently exert a repulsive force that acts to keep the particles away from the membrane surface. Here, we theoretically …show moreCoating of filtration membranes with a polymer brush holds great promise for efficiently preventing the deposition of fouling particles. The polymer chains are compressed by incoming particles, carried with the permeation flow towards the membrane, and consequently exert a repulsive force that acts to keep the particles away from the membrane surface. Here, we theoretically investigate the effect of a polymer brush coating on the permeation-induced hydrodynamic force, Fh, pulling a particle towards the membrane, and its balance with the steric repulsion exerted by the compressing brush, resisting the particle's approach. Lubrication theory yields an ordinary differential equation for the pressure, from which Fh is calculated numerically. Further, an asymptotic analysis is performed for the limiting cases of a dilute or dense brush, providing analytic expressions that demonstrate how brush properties affect Fh. Finally, the equilibrium position of a particle is evaluated by considering a balance between the opposing forces. The results provide an upper boundary for the brush properties, beyond which the brush is barely compressed under conditions typical of membrane filtration processes. Further increasing the brush density or thickness only decreases the total system permeance, resulting in increased energy consumption. The results shed light on the mechanisms by which a polymer brush affects the forces acting on a foulant particle, providing quantitative measures for assessing the potential efficacy of brush coatings. show less
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Abstract
In order to solely rely on renewable and efficient energy sources, reliable energy storage and production systems are required. Hydrogen is considered an ideal solution as it can be produced electrochemically by water electrolysis and renewably while no pollutants are released when consumed. The most common catalysts in electrolyzers are composed of rare and expensive …show moreIn order to solely rely on renewable and efficient energy sources, reliable energy storage and production systems are required. Hydrogen is considered an ideal solution as it can be produced electrochemically by water electrolysis and renewably while no pollutants are released when consumed. The most common catalysts in electrolyzers are composed of rare and expensive precious group metals. Replacing these materials with Earth-abundant materials is important to make these devices economically viable. Metal organic frameworks are one possible solution. Herein we demonstrate the synthesis and characterization studies of metal benzene-tri-carboxylic acid-based metal-organic frameworks embedded in activated carbon. The conductive composite material was found to be electrocatalytically active for both the oxygen evolution reaction and the hydrogen evolution reaction. Furthermore, several metal organic frameworks sharing the same ligand but with different first-row transition metals (M = Co, Cu, Fe, Mn) were compared, and the trend of their activity is discussed. Cobalt was found to have the highest activity among the studied metal centers, and therefore has the best potential to serve as a bifunctional catalyst for alkaline electrolyzers. show less
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Abstract
Porous carbons are of interest for a wide range of advanced‐technology ‘green’ energy applications including fuel cells, hydrogen storage, supercapacitors and batteries. Functional groups, heteroatoms and a more accessible hierarchical porous structure would be advantageous for many of these applications. This paper describes the generation of carbonaceous monoliths …show morePorous carbons are of interest for a wide range of advanced‐technology ‘green’ energy applications including fuel cells, hydrogen storage, supercapacitors and batteries. Functional groups, heteroatoms and a more accessible hierarchical porous structure would be advantageous for many of these applications. This paper describes the generation of carbonaceous monoliths with hierarchically porous structures and nitrogen functionalities by using a one‐pot, simultaneous combination of hydrogel synthesis and hydrothermal carbonization (HTC) that involves templating within high internal phase emulsions (HIPEs). A carbon monolith with a density of 0.058 g cm−3, a highly interconnected, bimodal porous structure and an apparent specific surface area (SBET) of 101 m2g−1 was produced by carbonizing a HTC monolith based on 2‐hydroxyethyl methacrylate (HEMA) at 450 °C. SBET of 1540 m2g−1 was produced through subsequent chemical activation with ZnCl2 at 700 °C, but the overall residual mass (Rm) was only 9 wt%. Direct chemical activation of the HTC monolith, on the other hand, generated SBET of 1250 m2g−1 and an overall Rm of 28 wt%, corresponding to a higher apparent surface area per mass of HTC monolith. Carbon monoliths with N/C ratios of 0.09 and 0.07 were achieved using nitrogen‐rich monomers (acrylamide and vinylimidazole, respectively) as compared to the HEMA‐based carbon monolith with an N/C ratio of 0.03. This work demonstrates that the hierarchically porous structures and the chemical structures of these highly porous monoliths can be fine‐tuned by modifying the HIPE composition and/or the processing conditions. show less
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Abstract
Acoustic waves can be used for high-precision evaporation of droplets, allowing for fine control over the droplet diameter. Previous works considered the acoustic field as simply a means for generating relative velocity u1 between a droplet and its surrounding gas, which convects heat and mass from the droplet while oscillating. In the present work …show moreAcoustic waves can be used for high-precision evaporation of droplets, allowing for fine control over the droplet diameter. Previous works considered the acoustic field as simply a means for generating relative velocity u1 between a droplet and its surrounding gas, which convects heat and mass from the droplet while oscillating. In the present work, we experimentally examine the effects of an acoustic field fundamental characteristics – pressure and velocity distribution and the phase between them – on a droplet evaporation rate. Our results clearly show that the pressure and phase contribute to the evaporation, with the latter dramatically affecting the process. We propose a generalization to existing models that account only for variations in u1, and demonstrate how the new model outperforms its counterpart when fitted to the experimental data. Our generalized correlation increases R2 for fitting the experimental data from 0.82 to 0.94, when compared with a standard model that only accounts for relative velocity. The new insight may be utilized for enhancement and fine-tuned control over droplet evaporation via acoustics, to be used over a wide range of applications, including lab-on-a-droplet reactions and vapor transport in thermoacoustic devices. show less
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Abstract
Designing high voltage (>3 V) and stable electrochemical supercapacitors with low self‐discharge is desirable for the applications in modern electronic devices. This work demonstrates a 4 V symmetric supercapacitor with stabilized cycling performance through atomic layer deposition (ALD) of alumina (Al2O3) on the surface of activated carbon (AC) …show moreDesigning high voltage (>3 V) and stable electrochemical supercapacitors with low self‐discharge is desirable for the applications in modern electronic devices. This work demonstrates a 4 V symmetric supercapacitor with stabilized cycling performance through atomic layer deposition (ALD) of alumina (Al2O3) on the surface of activated carbon (AC). The 20‐cycle ALD Al2O3 coated AC delivers 84 % capacitance retention after 1000 charge/discharge cycles under 4 V, contrary to the bare AC cells having only 48 % retention. The extended cycling life is associated with the thickened Stern layer and suppressed oxygen functional group. The self‐discharge data also show that the Al2O3 coating enables AC cells to maintain 53 % of charge retention after 12 h, which is more than twice higher than that of bare AC cells under the same test protocol of 4 V charging. The curve fitting analysis reveals that ALD coating induced slow self‐discharge dominated by ion diffusion mechanism, thus enhancing the AC surface energy. show less
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Abstract
Trimetallic double hydroxide NiFeCo-OH is prepared by coprecipitation, from which three different catalysts are fabricated by different heat treatments, all at 350 °C maximum temperature. Among the prepared catalysts, the one prepared at a heating and cooling rate of 2 °C min-1 in N2 atmosphere (designated NiFeCo-N2 -2 °C) displays the …show moreTrimetallic double hydroxide NiFeCo-OH is prepared by coprecipitation, from which three different catalysts are fabricated by different heat treatments, all at 350 °C maximum temperature. Among the prepared catalysts, the one prepared at a heating and cooling rate of 2 °C min-1 in N2 atmosphere (designated NiFeCo-N2 -2 °C) displays the best catalytic properties after stability testing, exhibiting a high current density (9.06 mA cm-2 at 320 mV), low Tafel slope (72.9 mV dec-1 ), good stability (over 20 h), high turnover frequency (0.304 s-1 ), and high mass activity (46.52 A g-1 at 320 mV). Stability tests reveal that the hydroxide phase is less suitable for long-term use than catalysts with an oxide phase. Two causes are identified for the loss of stability in the hydroxide phase: a) Modeling of the distribution function of relaxation times (DFRT) reveals the increase in resistance contributed by various relaxation processes; b) density functional theory (DFT) surface energy calculations reveal that the higher surface energy of the hydroxide-phase catalyst impairs the stability. These findings represent a new strategy to optimize catalysts for water splitting. show less
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Abstract
Diverse types of feedback to energy consumers have been studied for reducing energy use. The effect of feedback on energy consumption ranges from nil to substantial, and formulating a feedback program faces great uncertainty. The challenge is to choose the feedback program to reliably achieve a specified reduction in energy use. The major uncertainty is in consumers’ …show moreDiverse types of feedback to energy consumers have been studied for reducing energy use. The effect of feedback on energy consumption ranges from nil to substantial, and formulating a feedback program faces great uncertainty. The challenge is to choose the feedback program to reliably achieve a specified reduction in energy use. The major uncertainty is in consumers’ responses. This article uses info-gap decision theory to model and manage this uncertainty. Info-gap theory is a non-probabilistic methodology for modeling and managing deep uncertainty by assessing robustness to uncertainty. Three main conclusions are reached. First, predicted outcomes are not a reliable basis for evaluating a proposed feedback program. Rather, the robustness to uncertainty should be used, as developed generically and demonstrated by example. Second, robustness trades off against quality of the outcome: robustness to uncertainty gets larger (which is good) as the required reduction of energy usage is diminished (which is bad). Third, the preference between alternative programs may change as the required level of reduction in energy use is altered. The info-gap analysis of robustness supports the evaluation of alternatives and their prioritization in light of confidence in outcomes as assessed by robustness to uncertainty. The analysis is illustrated with a realistic example. show less
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Abstract
The performance of organic solar cells (OSC) critically depends on the morphology of the active layer. After deposition, the active layer is in a metastable state and prone to changes that lead to cell degradation. Here, a high efficiency fullerene:polymer blend is used as a model system to follow the temperature-induced morphology evolution through a series of thermal …show moreThe performance of organic solar cells (OSC) critically depends on the morphology of the active layer. After deposition, the active layer is in a metastable state and prone to changes that lead to cell degradation. Here, a high efficiency fullerene:polymer blend is used as a model system to follow the temperature-induced morphology evolution through a series of thermal annealing treatments. Electron microscopy analysis of the nano-scale phase evolution during the early stages of thermal annealing revealed that spinodal decomposition, i.e. spontaneous phase separation with no nucleation stage, is possibly responsible for the formation of a fine scale bicontinuous structure. In the later evolution stages, large polycrystalline fullerene aggregates are formed. Optical microscopy and scattering revealed that aggregate-growth follows the Johnson–Mehl–Avrami–Kolmogorov equation indicating a heterogeneous transformation process, i.e., through nucleation and growth. These two mechanisms, spinodal decomposition vs. nucleation and growth, are mutually exclusive and their co-existence is surprising. This unexpected observation is resolved by introducing a metastable monotectic phase diagram and showing that the morphology evolution goes through two distinct and consecutive transformation processes where spinodal decomposition of the amorphous donor:acceptor blend is followed by nucleation and growth of crystalline acceptor aggregates. Finally, this unified thermodynamic and kinetic mechanism allows us to correlate the morphology evolution with OSC degradation during thermal annealing. show less
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Abstract
Decoupled water splitting is a promising new path for renewable hydrogen production, offering many potential advantages such as stable operation under partial-load conditions, high-pressure hydrogen production, overall system robustness, and higher safety levels. Here, the performance of electrospun core/shell nickel/nickel hydroxide anodes is demonstrated in an …show moreDecoupled water splitting is a promising new path for renewable hydrogen production, offering many potential advantages such as stable operation under partial-load conditions, high-pressure hydrogen production, overall system robustness, and higher safety levels. Here, the performance of electrospun core/shell nickel/nickel hydroxide anodes is demonstrated in an electrochemical-thermally activated chemical decoupled water splitting process. The high surface area of the hierarchical porous electrode structure improves the utilization efficiency, charge capacity, and current density of the redox anode while maintaining high process efficiency. The anodes reach average current densities as high as 113 mA cm−2 at a working potential of 1.48 VRHE and 64 mA cm−2 at 1.43 VRHE, with a Faradaic efficiency of nearly 100% and no H2/O2 intermixing in a membrane-free cell. show less
AbstractWater electrolysis is a promising approach toward low-cost renewable fuels; however, the high overpotential and slow kinetics limit its applicability. Studies suggest that either dinuclear copper (Cu) centers or the use of borate buffer can lead to efficient catalysis. We previously demonstrated the ability of peptoids-N-substituted glycine oligomers-to stabilize …show more
AbstractPhotosynthesis in deserts is challenging since it requires fast adaptation to rapid night-to-day changes, that is, from dawn’s low light (LL) to extreme high light (HL) intensities during the daytime. To understand these adaptation mechanisms, we purified photosystem I (PSI) from Chlorella ohadii, a green alga that was isolated from a desert soil crust, and …show more
AbstractCadmium chalcogenides–metal hybrid nanostructures play an important role in a wide range of applications and are key components in photocatalysis. Hence, great efforts have been devoted to the exploration of a variety of metal components, each offering different functionalities. Silver is a vital catalyst used in the production of major industrial chemicals, found in …show more
AbstractStable complexes with terminal triply bound metal-oxygen bonds are usually not considered as valuable catalysts for the hydrogen evolution reaction (HER). We now report the preparation of three conceptually different (oxo)molybdenum(V) corroles for testing if proton-assisted 2-electron reduction will lead to hyper-reactive molybdenum(III) capable of converting protons …show more
AbstractFlavin-dependent glucose dehydrogenases (FAD-GDH) are oxygen-independent enzymes with high potential to be used as biocatalysts in glucose biosensing applications. Here, we present the construction of an amperometric biosensor and a biofuel cell device, which are based on a thermophilic variant of the enzyme originated from Talaromyces emersonii. The enzyme overexpression …show more
AbstractHematite (α-Fe2O3) is a leading photoanode candidate for photoelectrochemical water splitting. Despite extensive research efforts, the champion hematite photoanodes reported to date have achieved less than half of the maximal photocurrent predicted by its bandgap energy. Here we show that this underachievement arises, to a large extent, because of …show more
AbstractFuel cell (FC) is an attractive green alternative for today's fuel combustion systems. In common FCs, a polymer electrolyte membrane selectively conducts protons but blocks the passage of electrons and fuel. Nafion, the current benchmark membrane material, has a superior conductivity owing to unique morphology comprising randomly oriented elongated ionic nanochannels …show more
AbstractFabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition …show more
AbstractThe use of photosystem II (PSII) in hybrid bio-photoelectrochemical cells for conversion of solar energy to electrical current is hampered by PSII's narrow absorption cross-section and the generally poor electrical connection between isolated complex and different anode materials. Here, we merge isolated market-grade spinach PSII with 25 nm cystamine-2,6-dichlorobenzoquinone …show more
AbstractSince effective thermal insulation of buildings could significantly decrease energy consumption worldwide, this study examined the potential of concrete tiles with complex geometries at improving thermal performance in building envelopes. The study focused on air flow characteristics that occur near the external surface of the tile, and their influence on the rate of …show more
AbstractIn recent decades, polymer electrolyte membrane fuel cell (PEMFC) technologies have attracted research attention as promising candidates for next-generation energy conversion systems. This work deals with the effect of operating conditions and the construction of a typical model for PEMFCs, using electrochemical impedance spectroscopy (EIS) and distribution of relaxation …show more
AbstractOptimizing the properties of the mosaic morphology of bulk heterojunction (BHJ) organic photovoltaics (OPV) is not only challenging technologically but also intriguing from the mechanistic point of view. Among the recent breakthroughs in studies of BHJ morphology, is the identification and utilization of a three-phase (donor/mixed/acceptor) BHJ, where the (intermediate) …show more
AbstractWe report on an intriguing aspect of the effects of microstructure and chemistry on thermoelectric (TE) transport properties of nanostructured Bi2Te3-based compounds that are associated with their topologically insulating (TI) nature. Nanograined n-type Bi2Te3 and Bi1.94Nd0.06Te3 samples were …show more
AbstractCarbon nanotubes (CNTs) are stiff, all-carbon macromolecules with diameters as small as one nanometer and few microns long. Solutions of CNTs in chlorosulfonic acid (CSA) follow the phase behavior of rigid rod polymers interacting via a repulsive potential and display a liquid crystalline phase at sufficiently high concentration. Here, we show that small-angle X-ray …show more
AbstractSingle and multirotor drones are increasingly used for commercial and humanitarian applications, including product delivery [1], disaster relief [2], wildlife tracking [3], agriculture [4], andlab-on-a-drone functions [5]. Their main advantages include vertical takeoff and landing (VTOL) capability, hovering, and autonomous flight over difficult [6] and complex terrains …show more
AbstractModern applications require high energy density lithium-ion batteries (LIBs), inciting the search for high capacity anode materials. Recently, Aluminum (Al) anodes have reemerged as Li-alloyed anode material, but so far have not presented sufficient performance with commercially acceptable mass loadings. Interestingly, the active material intrinsic conductivity is not …show more
AbstractHybrid halide perovskites (HHPs) exhibit exceptional photoelectric properties, facilitating highly efficient modern solar cells and photoconductive technologies. Both ion migration and intrinsic spontaneous polarization have been proposed as the main source of enhanced photoelectric activity, but the exact origin of the advantageous properties has remained elusive. Here …show more
AbstractPorous carbons are of interest for a wide range of advanced‐technology ‘green’ energy applications including fuel cells, hydrogen storage, supercapacitors and batteries. Functional groups, heteroatoms and a more accessible hierarchical porous structure would be advantageous for many of these applications. This paper describes the generation of carbonaceous monoliths …show more
AbstractAcoustic waves can be used for high-precision evaporation of droplets, allowing for fine control over the droplet diameter. Previous works considered the acoustic field as simply a means for generating relative velocity u1 between a droplet and its surrounding gas, which convects heat and mass from the droplet while oscillating. In the present work …show more
AbstractThe performance of organic solar cells (OSC) critically depends on the morphology of the active layer. After deposition, the active layer is in a metastable state and prone to changes that lead to cell degradation. Here, a high efficiency fullerene:polymer blend is used as a model system to follow the temperature-induced morphology evolution through a series of thermal …show more
AbstractDecoupled water splitting is a promising new path for renewable hydrogen production, offering many potential advantages such as stable operation under partial-load conditions, high-pressure hydrogen production, overall system robustness, and higher safety levels. Here, the performance of electrospun core/shell nickel/nickel hydroxide anodes is demonstrated in an …show more