Analyzing Electrochemical Impedance Spectroscopy (EIS) data measured on fuel cells is increasingly done by finding the Distribution Function of Relaxation Times (DFRT, also known as DRT). This has clear advantages in cases where the important loss mechanisms occur in series and at separable time constants. Then each peak may be attributed to a process, and its integral yields the effective loss associated with it. Recent advances in this field are briefly reviewed.

All-solid-state batteries (ASSBs) are poised to revolutionize energy storage due to their high energy density and enhanced safety. However, the inherent limitations of solid-solid interfaces, particularly poor interfacial contact and mechanical instability, remain critical challenges to practical deployment. Stack pressure has emerged as a powerful tool to improve interfacial contact, reduce impedance, and enable stable cycling performance. This review comprehensively elucidates how stack pressure governs the electrochemical and mechanical behavior of sulfide-based ASSBs. We examine how pressure influences densification and conductivity in sulfide SEs, mitigates void formation during Li plating/stripping, and affects particle contact and microstructure evolution in cathodes. While appropriately applied stack pressure can significantly enhance performance by improving interfacial contact and stability, excessive pressure may instead lead to mechanical degradation, including Li intrusion or active material fracture. We highlight recent experimental and modelling insights that reveal the chemo-mechanical coupling induced by pressure and emphasize the importance of pressure-specific design strategies for different electrode/electrolyte chemistries. Finally, we outline key prospects for enabling high-performance ASSBs through pressure regulation, material design, and advanced cell architectures.

While the low-temperature (50–80 °C) anion-exchange membrane water electrolysis (AEMWE) field is blooming, the potential for cell operation above 100 °C remains unexplored. Hereafter, we show the first high-temperature AEMWE (HT-AEMWE) cell operating at 110 °C under dry cathode operations with platinum-group metal-free catalysts. Increasing temperature strongly enhances OH– conductivity (119–216 mS/cm at 50–95 °C), water diffusivity (∼6.0-fold at 30–70 °C), and oxygen and hydrogen evolution reaction kinetics (∼30- and ∼6.0-fold increases, at 10–70 °C), altogether translated into substantial cell-level performance gains. The KOHaq-fed HT-AEMWE reaches >5 A/cm2 at <2.2 V and shows negligible degradation (4 μV/h) over a 500 h test at 1.0 A/cm2. Notably, the pure water-fed HT-AEMWE operated for 400 h at 110 °C and 0.5 A/cm2 is extremely stable (6 μV/h), suggesting that the HT-AEMWE technology can eliminate the need for an alkaline liquid electrolyte. This represents a significant landmark for the AEMWE technology.

The advancement of anion-exchange membrane fuel cells (AEMFCs) relies on the development of cost-effective and high-performance oxygen reduction reaction (ORR) catalysts. Here, we report the synthesis of metal-phthalocyanine (MPc) catalysts (M = Fe, Mn, Co, Cu, Ni, Li, Sn) via a simple, single-step, room-temperature ultrasonication process. N2 adsorption–desorption isotherms and X-ray diffraction (XRD) analyses confirm successful MPc deposition onto the Ketjen Black (KB) support. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) micrographs and the electron dispersive spectroscopy (EDS) maps reveal a homogeneous distribution of the MPc catalysts. FePc/KB, MnPc/KB, and CoPc/KB demonstrated significant ORR activity in rotating ring-disk electrode (RRDE) tests. When integrated into cathodes, the FePc-, MnPc-, CoPc-, CuPc-, and NiPc/KB catalysts exhibited good operando H2–O2 AEMFC performance. Among these, the FePc- and CoPc/KB catalysts achieved the highest specific peak power density of 524 and 605 mW mg–1, respectively, corresponding to 116% and 338% higher than the best performance previously reported for analogous nonpyrolyzed phthalocyanine-based catalysts. MnPc-, CuPc-, and NiPc/KB further confirmed the broad potential of MPc/KB catalysts as efficient AEMFC cathodes. This work establishes a direct correlation between the ORR catalytic performance of MPc/KB materials and their efficiency as AEMFC cathodes, offering valuable insights for future catalyst design and the widespread adoption of phthalocyanine-based catalysts and AEMFC technology.

The operation of anion-exchange membrane fuel cells (AEMFCs) under ambient air conditions (CO2-containing) presents a major challenge for this technology. Additionally, the inferior performance of platinum-group-metal (PGM)-free anodes also constitutes a serious challenge to operating AEMFCs. To establish this technology as a viable alternative to mainstream fuel cell technology, AEMFCs must demonstrate competitive performance while operating in ambient air and PGM-free catalysts at both electrodes. Here, we present a first-of-its-kind, completely PGM-free AEMFC with excellent performance showing record peak power density of 515 mW/cm2 under H2–O2 and 281 mW/cm2 under H2–ambient air─the latter, ten times higher (!) than the best-reported H2–ambient air PGM-free AEMFCs. This study represents a paradigm shift in the technology, finally demonstrating for the first time the full potential of the AEMFCs.

Zinc–air batteries (ZABs) with near-neutral electrolytes have recently gained attention as an alternative to alkaline ZABs, offering improved tolerance to ambient CO2, reduced corrosion, and possible reversibility improvements. However, their fundamental electrochemistry is poorly understood. Discharge pathways vary widely with the electrolyte composition, cathode properties, and cycling conditions, leading to conflicting reports on redox reaction mechanisms. Likewise, the dominant degradation modes remain unsettled. This Perspective highlights emerging insights into the redox chemistry and failure mechanisms of near-neutral ZABs, emphasizing conceptual uncertainties, literature inconsistencies, and overlooked variables. We identify knowledge gaps that prevent mechanism-informed design and systematic optimization. The goal of this work is to stimulate deeper mechanistic studies that move beyond empirical trends and establish a foundation for advancing near-neutral ZABs.

The energy-efficient extraction of oxygen directly from air remains a significant technological challenge. Anion-exchange membranes (AEMs) play a critical role in electrochemical systems due to their ability to provide high ionic conductivity and chemical stability, achieved through rational design of polymer backbones combined with functional cationic groups. In this study, we combine fuel cell and water electrolyzer electrodes to allow a unique electrochemical device to selectively extract oxygen from air. Specifically, we present a hydrophilic imidazolium group that was introduced as a “performance-assisting moiety” onto a poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) backbone to fabricate novel AEMs. The resulting membranes exhibited controlled water uptake of 21.2%–53.7%, moderate swelling ratios of 3.5%–18.3% below 70 °C, and satisfactory thermal and mechanical stability. Selected AEMs that demonstrated moderate ionic conductivity and ion exchange capacity (IEC) were incorporated into an electrochemical anion exchange membrane oxygen separator (AEMOS). The resultant device can achieve a high current density of 109 mA cm-2, reflecting its strong potential for efficient oxygen separation. This work presents a promising solid‐state and electrolyte‐free strategy for oxygen extraction, which is expected to contribute to the development of sustainable oxygen generation technologies.

Rechargeable magnesium batteries (RMBs) are a promising alternative to lithium-ion batteries because of the high capacity and crustal abundance of magnesium. However, RMBs are primarily plagued by low-energy-density of traditional cathode materials, which utilize transition-metal cationic redox chemistry. Herein, a new family of layered Ti1-xFexS2 (0 < x < 1) materials is proposed to assess anionic redox and boost the energy density of RMBs. The structural stability and redox activity are systematically investigated using first-principles calculations and operando experimental techniques. It is found that layered MgnTi1-xFexS2 materials are stable below x = 0.5, forming the solid-solution sulfides. The MgnTi0.75Fe0.25S2 sample is experimentally shown to offer a high operating voltage of 1.8 V, a competitive energy density of 103 mAh g−1, and better cycling stability compared to prototype TiS2 material. Both cations (Ti and Fe) and anion (S) are revealed to take part in the redox reaction. The new family of layered Ti1-xFexS2 cathodes with joint cationic and anionic redox chemistry proposed in this work are promising high-energy cathode candidates for RMBs.

In the quest for advanced energy storage solutions, the stability and performance of electrolyte materials are of paramount importance. In particular, the redox potentials of electrolytes are of great interest, as these values dictate the electrochemical window that can be applied during battery cycling. Although redox trends can be estimated from computed frontier orbital energies and ionization potentials (IPs) and electron affinities (EAs), accurately representing long-range electrostatics is challenging. While solution-phase embedding schemes (e.g., continuum solvation, cluster–continuum, and polarizable/frozen-density embedding) are well established, their direct application and validation in electrolyte systems remain limited. In the current study, we adopt an integrated approach, combining classical molecular dynamics (MD) simulations and quantum mechanics–molecular mechanics (QM/MM) calculations to estimate the electrochemical stability of electrolytes. MD simulations of the electrolytes are first used to generate representative solution configuration ensembles, which are then subjected to QM/MM calculations to determine the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and the vertical IP and EA. To account for long-range electrostatics and configurational sampling, we consider increasingly larger solvation shells surrounding electrolyte molecules and perform ensemble averaging. Using this framework, we specifically study two widely used electrolytes for lithium- and sodium-ion batteries and investigate the effect of anion additives. The computed results are compared with experimental results from linear sweep voltammetry. We conclude that it is important to include several solvation shells to accurately compute the frontier orbitals of electrolyte molecules and to average the orbitals over configuration ensembles. The current approach for the first time computes the oxidative and reductive stability trends of electrolyte species while capturing the long-range effects and configuration ensembles of the environment. We also observe that, while vertical IP and EA values strongly correlate with HOMO and LUMO energies, structural relaxation of oxidized and reduced species weakens this correlation─particularly for organic carbonates upon reduction─highlighting the limitations of the simple HOMO–LUMO picture and the need to account for geometric relaxation in realistic redox predictions.

Bimetallic catalysts offer enhanced catalytic performance through synergistic interactions between the two metals, allowing them to break the linear scaling relations and reach high electrocatalytic activity. This study presents bimetallic aerogel-based catalyst synthesized as a covalent, three-dimensional framework containing neighboring iron and manganese sites. The aerogel structure provides a high surface area and porosity, facilitating an ultra-high active site density and efficient mass transport. The MnFe porphyrrole's unique structure is obtained by alternately linking Mn-porphyrin and Fe-corrole complexes. It exhibited outstanding performance with an onset potential of 0.99 V_RHE. Comparative studies with a free-base Fe porphyrrole catalyst (E_onset 0.97 V_RHE) revealed that while Mn incorporation led to only a slight improvement in half-cell performance, it resulted in significantly enhanced performance in anion exchange membrane fuel cell. The MnFe catalyst achieved an OCV of 0.97 V and a peak power density of 0.27 W cm⁻², outperforming the free-base Fe counterpart. Using density functional theory calculations, we show that the higher ORR activity of MnFe-porphyrrole is due to charge transfer between Mn and Fe atoms, which is absent in the reference free-base Fe-porphyrrole. These findings underscore the advantages of bimetallic catalysts in improving ORR activity and fuel cell efficiency by leveraging synergistic effects.