One of the most important needs for the future of low-cost fuel cells is the development of highly active platinum group metal (PGM)-free catalysts. For the oxygen reduction reaction, Fe–N–C materials have been widely studied in both acid and alkaline media. However, reported catalysts in the literature show quite different intrinsic activity and in-cell performance, despite similar synthesis routes and precursors. Here, two types of Fe–N–C are prepared from the same precursor and procedure – the main difference is how the precursor was handled prior to use. It is shown that in one case Fe overwhelmingly existed as highly active single-metal atoms in FeN₄ coordination (preferred), while in the other case large Fe particles coexisting with few single metal atoms were obtained. As a result, there were drastic differences in the catalyst structure, activity, and especially in their performance in an operating anion exchange membrane fuel cell (AEMFC). Additionally, it is shown that catalyst layers created from single-atom-dominated Fe–N–C can have excellent performance and durability in an AEMFC using H₂/O₂ reacting gases, achieving a peak power density of 1.8 W cm⁻² – comparable to similar AEMFCs with a Pt/C cathode – and being able to operate stably for more than 100 h. Finally, the Fe–N–C cathode was paired with a low-loading PtRu/C anode electrode to create AEMFCs (on H₂/O₂) with a total PGM loading of only 0.135 mg cm⁻² (0.090 mg_Pt cm⁻²) that was able to achieve a very high specific power of 8.4 W mg_PGM⁻¹ (12.6 W mg_Pt⁻¹).

Wastewater streams contain a large number of contaminants, part of which can be quite toxic for the working bacteria in bioreactors, thus hampering its efficiency. In such cases, pretreatment by an Advanced Oxidation Process (AOP) might be needed. Since, in general, biotreatment is more economic than AOP, it is sensible to design the integrated system in a manner that would reduce the load on the AOP as much as possible. This is a very challenging task, since the type and the concentration of the toxic compounds constantly varies over time. The problem is aggravated by lack of inexpensive and fast technologies that are able to evaluate the toxicity under conditions in which the nature of the toxic compounds is unknown.

Here we report on the developing of a unit that automatically measures the extent by which polluted water might put at risk a biological treatment unit. The sensing unit monitors in real time the viability of the reporting bacteria Bacillus Subtilis, using resazurin. The toxic compounds were modelled by three antibiotics (chloramphenicol, tetracycline and ciprofloxacin). The potential of embedding the sensing unit in a multi-technology system (AOP-biological) was demonstrated by connecting the sensing unit to a photocatalytic reactor and controlling the number of operating lamps in the photocatalytic reactor autonomously according to predetermined toxicity setpoint. The approach can be easily applied to almost any AOP-biotreatment tandem system, while altering any controllable parameter (residence time, light, etc.) of the AOP unit according to needs.

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) 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.

Corroles, macrocycles that owe their name to the cobalt-chelating prosthetic group of vitamin B12 and share numerous features with the iron-chelating porphyrin present in heme proteins/enzymes, constantly cross new boundaries ever since stable derivatives became easily accessible. Particularly important is the increasing utilization of corroles and the corresponding metal complexes for the benefit of mankind, in terms of new drug candidates for treating various diseases and as catalysts for sustainable energy relevant processes. One challenge is to gain access to the plain macrocycle, as to allow for full elucidation of the most fundamental properties of corroles. We have obtained the substituent-free corrole by several surprising and conceptually different pathways. Selected features of the corresponding metal complexes are illuminated, for pointing towards unique phenomena that are anticipated to largely expand the horizon regarding their utilization for contemporary catalysis.

Energy storage needs to account for the intermittence of solar radiation if solar energy is to be used to answer the heat demands of buildings. Energy piles, which embed thermal loops into the pile body, have been used as heat exchangers in ground source heat pump systems to replace traditional boreholes. Therefore, it is proposed to store solar thermal energy underground via energy piles. To investigate the performance of such systems, a laboratory-scale coupled energy pile-solar collector system was built for this study. Experiments were performed to evaluate the effects of various controlling parameters on the short-term performance of the system. These include the degree of saturation of the soil, the flowrate of the heat-carrying fluid, the intensity of solar radiation, and their interaction. The results showed that under abundant solar radiation, the daily average rate of energy storage per unit pile length increases by about 150 W/m when the soil condition changes from being dry to saturated, with a maximum value of about 200 W/m. As the intensity of solar radiation drops, it becomes the dominant factor. Compared to the laminar flow, the turbulent flow contributes more to the underground solar energy storage as the soil is more saturated. This suggests a technique to minimise the electricity consumption by the system and thus optimise its performance through regulating the flowrate. In addition, a mathematical model of the coupled energy pile-solar collector system was validated against the measurements. Long-term simulations in prototype using the validated model further confirm the above conclusions.

Efforts to improve energy storage depend greatly on the development of efficient electrode materials. Recently, strain has been employed as an alternate approach to improve ion mobility. While lattice strain has been well-researched in catalytic applications, its effects on electrochemical energy storage are largely limited to computational studies due to complexities associated with strain control in nanomaterials as well as loss of strain due to the phase change of the active material during charging–discharging. In this work, we overcome these challenges and investigate the effects of strain on supercapacitor performance in Li-ion-based energy devices. We synthesize epitaxial Fe3O4@MnFe2O4 (core@shell) nanoparticles with varying shell thickness to control the lattice strain. A narrow voltage window for electrochemical testing is used to limit the storage mechanism to lithiation–delithiation, preventing a phase change and maintaining structural strain. Cyclic voltammetry reveals a pseudocapacitive behavior and similar levels of surface charge storage in both strained- and unstrained-MnFe2O4 samples; however, diffusive charge storage in the strained sample is twice as high as the unstrained sample. The strained-MnFe2O4 electrode exceeds the performance of the unstrained-MnFe2O4 electrode in energy density by ∼33%, power density by ∼28%, and specific capacitance by ∼48%. Density functional theory shows lower formation energies for Li-intercalation and lower activation barrier for Li-diffusion in strained-MnFe2O4, corresponding to a threefold increase in the diffusion coefficient. The enhanced Li-ion diffusion rate in the strained-electrodes is further confirmed using the galvanostatic intermittent titration technique. This work provides a starting point to using strain engineering as a novel approach for designing high performance energy storage devices.

A pattern of sequential group-by-group charging or discharging, of Li batteries with phase-separation thermodynamics, was detected by numerical simulations and justified by several experiments published in literature. The present work is the first to quantitatively predict the main characteristics of the sequential symmetry breaking (SB) events, such as the average Li concentration and the fraction of the Li-poor part at the SB transition times. Using a reduced two-zone (Li-poor and Li-rich) model, that ignores gradients in the liquid phase potential (ϕ_l), we derive an approximate solution predicting the effect of non-uniformity in initial conditions or in imposed parameter (collectively referred to as 'noise') on the characteristics. We show that gradients in ϕ_l, although extremely small, operate like noise leading to break-up of the homogeneous solution. A bifurcation map, showing the lowest current boundary that ensures a homogeneous lithiation/ delithiation as a function of noise level, is constructed.

In recent years, finding alternatives for fossil fuels has become a major concern. One promising solution is microorganism-based bio-photo electrochemical cells (BPECs) that utilize photosynthetic solar energy conversion as an energy source while absorbing CO₂ from the atmosphere. It was previously reported that in cyanobacterial-based BPECs, the major endogenous electron mediator that can transfer electrons from the thylakoid membrane photosynthetic complexes and external anodes is NADPH. However, the question of whether the same electron transfer mechanism is also valid for live eukaryotic microalgae, in which NADPH must cross both the chloroplast outer membrane and the cell wall to be secreted from the cell has remained elusive. In this work, we show that NADPH is also the major endogenous electron mediator in the microalgae Dunalliela salina (Ds). We show that the ability of Ds to tolerate high salinity enables the production of a photocurrent that is 5–6 times greater than previously reported for freshwater cyanobacterial-based BPECs in the presence or absence of exogenous electron mediators. Additionally, we show that the electron mediator Vitamin B1 can also function as an electron mediator enhancing photocurrent production. Finally, we show that the addition of both FeCN and NADP⁺ to Ds has a synergistic effect enhancing the photocurrent beyond the effect of adding each mediator separately.

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 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.

This paper presents the utilization of hybrid carbon nano-tube (CNT) – manganese dioxide (MnO₂) tissues as air electrodes in nonaqueous aluminum- and lithium-based battery systems. The CNT tissues are impregnated with α-manganese dioxide nanoparticles via a straightforward binder-free ultrasonic treatment, thereby enabling an improved oxygen reduction reaction (ORR) catalytic activity. Half-cell potentiodynamic measurements along with full-cell discharge evaluations of Li- and Al-based battery systems are reported. Higher discharge potentials and capacities were obtained from generic and advanced hybrid CNT–MnO₂ air cathodes. The discharge products obtained on the air cathode surface were studied using high-resolution scanning electron microscopy. Their chemical compositions were evaluated using elemental mapping energy-dispersive X-ray spectroscopy. We complemented our analysis with density functional theory calculations of oxygen adsorption on MnO₂ and graphene. The modifications obtained for the discharge products in both systems, along with their improved distribution within the cathode surface, supported longer discharge processes without clogging the O₂ penetration pathways at the air cathode. The stability of the α-MnO₂ catalyst was studied using X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, thereby indicating the ongoing formation of an outer MnF₂ shell layer, which affected the α-MnO₂ functionality, as an efficient ORR catalyst.

Many efforts have been directed towards elucidating the nitrogenase structure, its biocatalytic activity, and methods to artificially activate it by external stimuli. Here, we investigated how semiconductor nanoparticles (NPs) with sizes ranging between 2.3–3.5 nm form nano-biohybrids with the nitrogenase enzyme and enable its photoinduced biocatalytic activity. We examined two homogenously synthesized quantum dots (QDs), CdS, CdSe, and two nitrogenase variants, the wild-type and a cysteine-mutated. We show that the cysteine-mutated variant does not enhance the hydrogen generation amounts, as compared with the wild type. Nevertheless, we show that the 2.3 nm-sized CdSe NPs facilitate an eightfold increase compared with larger CdSe NPs. The obtained results were investigated using electrochemical techniques, transmission electron microscopy, and further confirmed by time-resolved spectroscopic measurements, which allow us to determine the electron tranfer rate constant (k_ET) of the different configurations.

The desalination fuel cell (DFC) is a novel technology for co-production of electricity and desalinated water from a clean energy source, the H₂/O₂ redox couple. A DFC utilizes a fuel cell anode and cathode to catalyze the chemical-to-electrical energy conversion, as well as a cation and anion exchange membrane to desalinate the feedwater flowing through the cell. To identify key bottlenecks in this nascent technology, it is important to quantify voltage losses associated with major elements of the cell. We here provide first-time detailed experimental breakdowns of voltage losses at electrodes and across membranes in a custom-built DFC, operated both with near-neutral pH water streams and in a pH-gradient mode. The results allow us to pinpoint sources of major voltage losses, provide hypothesis for underlying causes, and can serve to focus future DFC materials development and cell engineering efforts.

Fe–N–C electrocatalysts hold a great promise for Pt-free energy conversion, driving the electrocatalysis of oxygen reduction and evolution, oxidation of nitrogen fuels, and reduction of N2, CO2, and NOx. Nevertheless, the catalytic role of iron carbide, a component of nearly every pyrolytic Fe–N–C material, is at the focus of a heated controversy. We now resolve the debate by examining a broad range of Fe3C sites, spanning across many typical size distributions and carbon environments. Removing Fe3C selectively by a non-oxidizing acid reveals its inactivity towards two representative reactions in alkaline media, oxygen reduction and hydrazine oxidation. The activity is assigned to other pre-existing sites, most probably Fe-Nx. DFT calculations prove that the Fe3C surface binds O and N intermediates too strongly to be catalytic. By settling the argument on the catalytic role of Fe3C in alkaline electrocatalysis, we hope to spur innovation in this critical field.

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 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.

Here we propose a novel way to prevent the insidious effect of carbon corrosion in a Proton Exchange Membrane Fuel Cell (PEMFC) by depositing a corrosion-resistant layer (~1.5 nm thick) of Titanium Nitride (TiN) on the carbon substrate of platinum on carbon (Pt/C) catalyst (in powder state), leaving the Pt catalyst centers uncoated and accessible for reagents reactions (oxygen O2 and H+ protons). The deposition was carried out at 150°C with a Hollow-Cathode Plasma-Assisted Atomic Layer Deposition (HCPA-ALD) using Tetrakis(dimethylamino)titanium (IV) (TDMAT) as the metal precursor in Ar/N2 plasma, from which nitrogen was used as co-reactant. Additionally, Transmission Electron Microscopy (TEM) characterization allowed us to prove the successful formation of a homogenous coating on these nanoparticles and electrochemical characterization performed with a Rotating Disc Electrode (RDE) further confirmed the activity and effectiveness of our designed catalyst. Preliminary results have shown that highly conformal TiN can be successfully grown onto Pt/C nanoparticles by using HCPA-ALD with a custom-made agitator mechanism.

As countries worldwide are integrating more energy storage systems and renewable energy sources, it is important to examine how these impact the frequency stability of the grid. In this study we explore this question by focusing on Israel in 2025. Based on the Israeli power grid model in 2025, which includes detailed information on the entire transmission network, generation units, and loads, we examine hundreds of different locations and sizes of renewable energy sources and energy storage systems, focusing on the frequency behavior in each scenario following the loss of a large generator. This is done using the industry-standard PSS/E simulator. The results lead to several design-level recommendations. One main conclusion is that the Israeli power system already has the required resources to maintain frequency stability in case a large generation unit is lost. However, to maintain a reliable system, policy makers should encourage that the existing and additional storage will contribute to frequency regulation when there is a risk of instability. We also find that the location of renewable energy sources and energy storage systems has an impact on the frequency stability, and that it is better to place storage systems in the south, and renewable energy sources in the north. However, at least until 2025 this impact is not yet strong enough to be a leading factor in determining the location of these sources.

Photoinduced electron transfer systems can mimic certain features of natural photosynthetic reaction centers, which are crucial for solar energy production. Among other tetra-pyrroles, the versatile chemical and photophysical properties of corroles make them very promising donors applicable in donor-acceptor complexes. Here, we present a first comprehensive study of ultrafast photoinduced electron transfer in a self-assembling sulfonated aluminum corrole-methylviologen complex combining visible and mid-IR transient absorption spectroscopy. The noncovalent D-A association of the corrole-methylviologen complex has the great advantage that photoinduced charge separation becomes possible even though the back electron transfer (BET) rate is large. Initial forward electron transfer from corrole to methylviologen is observed on an ∼130 fs time scale. Subsequent back electron transfer takes place with τBET = (1.8 ± 0.5) ps, revealing very complex relaxation dynamics. Direct probing in the mid-IR allows us to unravel the back electron transfer and cooling dynamics/electronic reorganization. Upon tracing the dynamics of the methylviologen-radical marker band at 1640 cm-1 and the C═C stretching of corrole at around 1500 cm-1, we observe that large amounts of excess energy survive the back transfer, leading to the formation of hot ground state absorption. A closer examination of the signal after 300 ps, surviving the back transfer, exhibits a charge-separation yield of 10-15%.

Biomass is a promising renewable feedstock to produce polyisoprene for the rubber industry. Through metabolic engineering, sugars derived from pretreated and hydrolyzed cellulose and hemicellulose can be directly fermented to isoprene to produce rubber. Here we investigate the life cycle environmental impact of isoprene fermentation to produce bio-polyisoprene from agricultural residues (of Zea mays L.). Results show that the greenhouse gas (GHG) intensity of bio-polyisoprene (−4.59 kg CO₂e kg⁻¹) is significantly lower than that of natural rubber (Hevea brasiliensis) and synthetic rubber (−0.79 and 2.41 kg CO₂e kg⁻¹, respectively), while supporting a circular biogenic carbon economy. We found the land use intensity of bio-polyisoprene to be 0.25 ha metric ton⁻¹, which is 84% lower than that from rubber tree plantations. We compare the direct fermentation to isoprene results with indirect fermentation to isoprene through the intermediate, methyl butyl ether, where dehydration to isoprene is required. The direct fermentation of isoprene reduces reaction steps and unit operations, an expected outcome when employing process intensification, but our results show additional energy conservation and reduced contribution to climate change. Among the ReCiPe life cycle environmental impact metrics evaluated, air emission related impacts are high for bio-polyisoprene compared to those for natural and synthetic rubber. Those impacts can be reduced with air emission controls during production. All other metrics showed an improvement for bio-polyisoprene compared to natural and synthetic rubber.

Efforts to replace fossil fuels with renewable energy technologies, especially solar energy conversion, continue to improve the potential to produce useful amounts of energy without significant pollution. Utilization of photosynthetic organisms in bio-photo electrochemical cells (BPECs) are a potentially important source of clean energy. Here, we show that it is possible to harvest photocurrent directly from unprocessed plant tissues in specialized BPECs. The source of electrons are shown to originate from the Photosystem II water-oxidation reaction that results in oxygen evolution. In addition to terrestrial and crop plants, we further demonstrate the ability of the desert plant Corpuscularia lehmannii to produce bias-free photocurrent without the addition of an external electrolyte. Finally, we show the use of pond-grown water lilies to generate photocurrent. Different leaves produce photocurrent densities in the range of ∼ 1 – 10 mA / cm2 which is significantly higher than microorganism-based BPECs. The relatively high photocurrent and the simplicity of the plants BPEC may pave the way toward the establishment of first applicative photosynthetic based energy technologies.

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 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.

Anion-exchange membrane fuel cells (AEMFCs) are rapidly gaining visibility in the clean energy research field due to their high power output and potential to significantly reduce materials costs. However, despite the high performances obtained, in-operando stability still presents a major obstacle for this technology. The durability issues are usually attributed to the core component of the AEMFCs - the anion-exchange membrane (AEM). An easy and simple way to produce these AEMs is through radiation grafting. Radiation-induced processes involve changes in the intrinsic properties of the polymer that can promote both crosslinking and chain scissioning, which may directly affect the mechanical properties and durability of AEMs. This study presents a comprehensive report of the effects of irradiation on the final properties of electron-beam grafted ETFE-AEMs. The results strongly suggest that low absorbed doses (<40 kGy) and an inert atmosphere (N₂) should be used during the irradiation process in order to obtain better backbone stability and, consequently, AEMFC durability, considering ETFE-based AEMs.

Lanthanum molybdenum oxide (La₂Mo₂O₉, LAMOX)-based ion conductors have been used as potential electrolytes for solid oxide fuel cells. The parent compound La₂Mo₂O₉ undergoes a structural phase transition from monoclinic (P2₁) to cubic (P2₁3) at 580 °C, with an enhancement in oxide ion conductivity. The cubic phase is of interest because it is beneficial for oxide ion conduction. In search of alternative candidates with a similar structure that might have a stable cubic phase at lower temperatures, we have studied the variations of the crystal structure and ionic conductivity for 25, 50, 62.5 and 75 mol% W substitutions at the Mo site using high-temperature X-ray diffraction, dilatometry, and impedance spectroscopy. Highly dense ceramic samples have been synthesized by solid-state reaction in a two-step sintering process. Low-angle X-ray diffraction and Rietveld refinement confirm the stabilization of the cubic phase for all compounds in the entire temperature range considered. The substitutions of W at the Mo site produce a decrement in the lattice parameter. The thermal expansion coefficients in the high-temperature range of the W-substituted ceramics, as determined by dilatometry, are much higher than that of the unmodified sample. The impedance spectra have been modeled using a modified genetic algorithm within 300–600 °C. A distribution function of the relaxation times is obtained, and the contributions of ohmic drop, grains and grain boundaries to the conductivity have been identified. Overall, our investigation provides information about cationic substitution and insights into the understanding of oxide ion conductivity in LAMOX-based compounds for developing solid oxide fuel cells.

Branched nanostructures have attracted considerable interest due to their large surface-to-volume ratio with benefits in photocatalysis and photovoltaic applications. Here we discuss the tailoring of branched structures with a shape of a star based on PbS semiconductor. It exposes the reaction mechanism and the controlling factors that template their morphology. For this purpose, we varied the primary lead precursors, types of surfactant, lead-to-surfactant molar ratio, temperature and duration of the reaction. Furthermore, intermediate products in a growth reaction were thoroughly examined using X-ray diffraction, transmission electron microscopy, Raman scattering, optical absorbance and Fourier transform infrared spectroscopy. The results designated a primary formation of truncated octahedral seeds with terminating {100} and {111} facets, followed by the selective fast growth of pods along the 〈100〉 directions toward the development of a star-like shape. The examined intermediates possess a cubic rock salt structure. The observations indicated that small surfactant molecules (e.g. acetate) evolve the branching process, while long-chain surfactants (e.g. oleate) stabilize the long pods as well as mitigate the aggregation process. This study conveys fundamental knowledge for the design of other branched structures, that are attractive for practical use in catalysis, electrochemistry and light-harvesting.

In recent decades, rechargeable Mg batteries (RMBs) technologies have attracted much attention because the use of thin Mg foil anodes may enable development of high-energy-density batteries. One of the most critical challenges for RMBs 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. Herein, the feasibility of processing ultrathin Mg anodes in electrochemical cells was demonstrated by using AZ31 Mg alloys (3 % Al; 1 % Zn). Thin-film Mg AZ31 anodes presented reversible Mg dissolution and deposition behavior in complex ethereal Mg electrolytes solutions that was comparable to that of pure Mg foils. Moreover, it was demonstrated that secondary Mg battery prototypes comprising ultrathin AZ31 Mg alloy anodes (≈25 μm thick) and Mg_xMo₆S₈ Chevrel-phase cathodes exhibited cycling performance equal to that of similar cells containing thicker pure Mg foil anodes. The possibility of using ultrathin processable Mg metal anodes is an important step in the realization of rechargeable Mg batteries.

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 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.

The urgent need for fresh water remains a strong driver for reverse-osmosis (RO) desalination, but present-day systems are energy-inefficient and produce significant green-house gas emissions. This motivated our research, which introduces and investigates a novel concept for wind-driven RO desalination. It is based on the Coanda effect, applied periodically by blowing slots on a spring-stabilized vertical cylinder, to produce reciprocating motion that drives RO piston pumps. The Coanda-based Reciprocating (CoRe) system converts wind energy directly to mechanical pumping energy thereby eliminating generator and motor inefficiencies. A small-scale (2-m high) system was constructed and evaluated in an open-jet wind tunnel. It delivered 2–6 bars of water pressure with a net power efficiency of up to 4% depending on wind speed and circulation control parameters. A mathematical model of the system produced excellent correspondence with the experimental data. It was determined that the experimental setup and slot design biased the results negatively and model predictions based on published Coanda data indicated net power efficiencies up to 20%. It was also determined that the slot design details had a decisive effect on performance.

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 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.

The morphology development of polymer-based blends, such as those used in organic photovoltaic (OPV) systems, typically arrests in a state away from equilibrium – how far from equilibrium this is will depend on the materials chemistry and the selected assembly parameters/environment. As a consequence, small changes during the blend assembly alter the solid-structure development from solution and, in turn, the final device performance. Comparing an open-cage ketolactam fullerene with the prototypical[6,6]-phenyl-C61-butyric acid methyl ester in blends with poly[2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), we demonstrate that experimentally established, non-equilibrium temperature/composition phase diagrams can be useful beyond rationalization of optimum blend composition for OPV device performance. Indeed, they can be exploited as tools for rapid, qualitative structure–property mapping, providing insights into why apparent similar donor:acceptor blends display different optoelectronic processes resulting from changes in the phase-morphology formation induced by the different chemistries of the fullerenes.

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 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.

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 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 (PSI_LL) and high light (PSI_HL), 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 PSI_HL to minimize the photodamage. An additional change is in the pigment composition and their number in LHCI_HL; about 50% of chlorophyll b is replaced by chlorophyll a. This leads to higher electron transfer rates in PSI_HL and might enable C. ohadii PSI to act as a natural photosynthesiser in photobiocatalytic systems. PSI_HL or PSI_LL were attached to an electrode and their induced photocurrent was determined. To obtain photocurrents comparable with PSI_HL, 25 times the amount of PSI_LL was required, demonstrating the high efficiency of PSI_HL. Hence, we suggest that C. ohadii PSI_HL is an ideal candidate for the design of desert artificial photobiocatalytic systems.

This paper presents estimations for life cycle energy demand, human toxicity, and climate change of industrial-scale production of A-site cation precursor chemicals that may be used in production of perovskite solar cells. We employed process scale-up concepts, updated data sources and industry-relevant process modelling assumptions to build commercially relevant life cycle inventories (LCIs) for each of the perovskite precursors. Life cycle assessment (LCA) was applied to characterize and compare the resulting life cycle impacts and comparisons were made with other module components. The main finding of this work is that precursor impacts are similar to each other and about 1,000 times less than solar glass. Therefore, selection of perovskite compositions for commercialization should be driven solely by efficiency and stability rather than environmental concerns.

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 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.

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 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.

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 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.

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 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.

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 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 -NH₂ 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.

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 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.

District heating (DH) systems can improve energy efficiency, reduce greenhouse gas (GHG) emissions, and be a cost-effective residential space heating alternative over conventional decentralized heating. This study uses radiative forcing (RF), a time-sensitive life cycle assessment metric, to evaluate space heating alternatives. We compare forest residue and willow biomass resources and natural gas as fuel sources against decentralized heating using heating oil. The comparison is performed for selected locations in the Northeastern United States over a 30-year production timeline and 100 observation years. The natural gas and willow scenarios are compared with scenarios where available forest residue is unused and adds a penalty of GHG emissions due to microbial decay. When forest residues are available, their use is recommended before considering willow production. Investment in bioenergy-based DH with carbon capture and storage and natural-gas-based DH with carbon capture and storage (CCS) technology is considered to assess their influence on RF. Its implementation further improves the net carbon mitigation potential of DH despite the carbon and energy cost of CCS infrastructure. Soil carbon sequestration from willow production reduces RF overall, specifically when grown on land converted from cropland to pasture, hay, and grassland. The study places initial GHG emissions spikes from infrastructure and land-use change into a temporal framework and shows a payback within the first 5 years of operation for DH with forest residues and willow.

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 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.

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 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.

Sr surface segregation (SSS) in perovskite materials is a main factor causing efficiency degradation of solid oxide fuel cells (SOFC's), and therefore can affect the La_0.3Sr_0.7Fe_0.7Cr_0.3O_3−δ perovskite, which is known as a compatible anode and cathode in a reversible and symmetric SOFC. As a result of segregation, the atomic rearrangements in the near-surface environment are likely to generate additional phases to the original one such as strontium carbonate (SrCO₃) at high CO₂ pressure. In the current work, first principal calculations are carried out for modeling the initial formation of SrCO₃ after Sr segregation in LSFCr with CO₂ presence. It is found that the tendency of CO₂ to participate in SrCO₃ phase formation is a competing reaction to its reduction to CO on the LSFCr material, and O vacancies are needed not only to improve CO₂ reduction but also to block the competing reaction of SrCO₃ adsorption. Therefore, LSFCr successfully “raises the bar” of CO₂ reduction catalytic efficiency by preventing unwanted Sr segregation at high concentrations of surface oxygen vacancies.

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 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.

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 < 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.

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 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.

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 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.

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 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

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 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.

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 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.

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 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.

Imposing a temperature gradient on a narrow channel can trigger an acoustic instability, driving self-sustained oscillations of the fluid. The temperature gradient required to trigger the instability is dramatically decreased when the channel wall is covered by a thin film of volatile liquid that can undergo phase change. In the present work, we consider a volatile-droplet aerosol on which a temperature gradient is imposed, and theoretically examine whether the heat and mass transfer between the droplets and gas can trigger the acoustic instability. The aerosol structure is separated into two disparate scales: the droplet ensemble, modelled as a periodic grid of channels through which the gas flows, and the ‘micro-scale’, in which the flow around a single droplet serves as an elementary unit in the periodic structure. This scale separation led to the derivation of a new function that accounts for losses caused by viscous, thermal and diffusive relaxation processes due to droplet–gas interactions. A stability analysis is then performed, utilising the derived ‘loss’ function, calculating the minimum temperature difference, \(\varDelta T\), that triggers the instability. Our analysis suggests that a non-uniform temperature distribution across aerosols may lead to an acoustic instability, which can subsequently enhance coalescence and agglomeration of droplets within an aerosol. Such phenomenon may be utilised to trigger or enhance the operation of thermoacoustic engines, and may possibly occur naturally in atmospheric clouds due to uneven solar irradiation.

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 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.

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 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.

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 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.

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 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.

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 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.

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 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.

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 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.

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 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.

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 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.

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 (cys-DCBQ) modified Au-nanoparticles (PSII–AuNP_Cys-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 AuNP_Cys-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).

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 reaction (ORR) electrocatalyst. The resonance frequency shift was measured on an Au/MnO_x 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.

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 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.

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 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.

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 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.

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 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.

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 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.

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 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.

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 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.

Although light is the driving force of photosynthesis, excessive light can be harmful. One of the main processes that limits photosynthesis is photoinhibition, the process of light-induced photodamage. When the absorbed light exceeds the amount that is dissipated by photosynthetic electron flow and other processes, damaging radicals are formed that mostly inactivate photosystem II (PSII). Damaged PSII must be replaced by a newly repaired complex in order to preserve full photosynthetic activity. Chlorella ohadii is a green microalga, isolated from biological desert soil crusts, that thrives under extreme high light and is highly resistant to photoinhibition. Therefore, C. ohadii is an ideal model for studying the molecular mechanisms underlying protection against photoinhibition. Comparison of the thylakoids of C. ohadii cells that were grown under low light versus extreme high light intensities found that the alga employs all three known photoinhibition protection mechanisms: (i) massive reduction of the PSII antenna size; (ii) accumulation of protective carotenoids; and (iii) very rapid repair of photodamaged reaction center proteins. This work elucidated the molecular mechanisms of photoinhibition resistance in one of the most light-tolerant photosynthetic organisms, and shows how photoinhibition protection mechanisms evolved to marginal conditions, enabling photosynthesis-dependent life in severe habitats.

Electrocatalysis of hydrazine oxidation, a promising carbon-free fuel, is both a practical goal, and a scientific paradox. Hydrazine is a common reductant in chemical synthesis, yet the onset potential for its electro-oxidation reaction is highly dependent on the catalytic surface. Some excellent catalysts have been developed in recent years towards this goal, designed for direct hydrazine fuel cells and for sensors. Most of these catalysts, however, are either prohibitively expensive (e.g. Pt-based ones), or easily deactivated (e.g Ni-based ones). We have recently discovered a family of multi-doped carbons with excellent electrocatalytic activity towards hydrazine oxidation in alkaline pH.1,2 They contain many components, all of which were hypothesized as candidates for hydrazine oxidation active sites: from Mo-doped Fe3C nanoparticles, to single-atom metal sites, and to the N-doped, hierarchically porous carbon. They seemed to provide the first example of hydrazine oxidation on carbides. Moreover, they are stable, efficient, and easy to make on a large scale. We then set out to understand the source of activity in these fascinating materials, and arrived at a range of surprising discoveries. First, we discovered how Mo-doping is actually unnecessary, and how Zn and Cu direct the nanostructure by different mechanisms.2 Then, we demonstrated that an N-doped carbon matrix – completely metal-free – is also highly active toward the reaction.3 At this point, we raised even larger questions: are the carbide nanoparticles even participate in the reaction? What does it really take for a carbon material to electro-oxidize hydrazine? To answer these questions, we combined electrochemical measurements, broad scope material characterization, and mechanistic quantum-mechanical calculations.4 In this talk I will present unpublished and recently published results, clearing the field of hydrazine oxidation on doped carbons, and explaining the individual catalytic, cooperative and structural roles of each component. While much remains to be understood about the activity and selectivity of these elusively simple material, and their excellent performance makes this challenge both technologically and scientifically appealing.

Defect chemistry plays a major role in the operation of perovskites cells. On one hand they are behind the remarkable self-healing,[1] while on the other they dictate the level of traps, non-radiative recombination,[2] as well as promote ion migration.[3] Moreover, once ions reach the electrodes the device degradation is accelerated.[4, 5] Combining the various reports it seems that if the perovskite would not lose its constituents it would self-heal and if it do lose them it is game-over. We claim that ion migration into the blocking layer is the most important electrochemical process standing in the way of long-term stability. As we will show at the presentation, a significant part of the electrochemistry behind ion leakage and consequently electrode reactions, is captured by a semiconductor device model that accounts for mixed electronic-ionic conduction.[6] While the mere transport of ions introduces no device degradation, introducing oxidation/reduction reactions at the electrodes reproduces the effect of light & bias on device stability. Lastly, we'll discuss if it is possible to design the device to mitigate this ion leakage out of the perovskite layer.

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) 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.

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 Bi_1.94Nd_0.06Te₃ 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.

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 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.

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 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.

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 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.

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 [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.

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 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.

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, 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.