Electrochemical conversion of CO₂ into calcium carbide in molten salts has emerged as a promising route for carbon capture and utilization, enabling the production of acetylene, an important industrial chemical. However, continuous operation requires a stable oxygen evolution reaction (OER) at the anode while suppressing competing oxidation of carbonate and carbide species that regenerate CO₂. The anodic reaction mechanism in carbide-containing molten salts remains poorly understood. Here, the anodic behavior and durability of the perovskite oxide La_0.7Sr_0.3FeO_3−δ are investigated in molten NaCl–CaCl₂ at 873 K under controlled anionic environments containing O²⁻, CO₃²⁻, and C₂²⁻. Thermodynamic analysis using potential–pO²⁻ diagrams predicts that carbide oxidation occurs at the most negative potential, followed by carbon, oxide, and carbonate oxidation, which agrees with electrochemical measurements and gas analysis. When O²⁻ and CO₃²⁻ coexist, selective oxygen evolution is achieved with a Faradaic efficiency of 81.4 % and a low corrosion rate of 1.94 × 10⁻⁵ g cm⁻² h⁻¹. In contrast, dissolved C₂²⁻ undergoes anodic oxidation at lower potentials, producing amorphous carbon that accelerates electrode degradation and reduces OER efficiency. These results demonstrate that anodic stability is governed by the local anionic environment, highlighting the importance of maintaining O²⁻ and CO₃²⁻ coexistence while suppressing carbide transport to the anode.

Suppressing zincate crossover is necessary for rechargeable alkaline Zn-MnO₂ rechargeable batteries using electrolytic manganese dioxide (EMD). We benchmarked six commercial separators for their ability to block zincate ions while maintaining the transport of hydroxide ions. Among the separators, FAAM-75-PK (FP75), a commercial anion-exchange membrane, exhibited moderate conductivity (5.8 mS cm⁻¹) with the lowest diffusion coefficient of zincate ions (D_Zn = 2.0 × 10⁻⁸ cm² s⁻¹) and a moderate diffusion coefficient of hydroxide ions (D_OH = 3.5 × 10⁻⁵ cm² s⁻¹), leading to the highest permselectivity (D_OH/D_Zn = 1.7 × 10³). In the galvanostatic discharge–charge tests, FP75 exhibited the best capacity retention of 68 % at the 7th cycle. Characterization of the discharged EMD electrodes revealed that FP75 effectively suppressed ZnMn₂O₄ formation at the cathode, favoring Mn₃O₄ formation instead. The low Zn concentration of 6 ppm in the catholyte is consistent with the favored Mn₃O₄ formation. Beaker-cell tests identify a system-dependent zinc concentration threshold. When the Zn/Mn molar ratio exceeds ∼0.05–0.15, product formation shifts toward ZnMn₂O₄ from Mn₃O₄, and thus, the capacity decay accelerates.

It is important to develop a rechargeable battery that is safe and free from resource risk to replace the current lithium–ion battery in various application fields. We have been conducting research and development of aqueous electrolyte batteries with zinc as the negative electrode (anode) through national programs, Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING, RISING2 and RISING3), commissioned by the New Energy and Industrial Technology Development Organization (NEDO). In RISING2, we demonstrated a full cell that can achieve a target specific energy of 500 Wh kg⁻¹ for a zinc–air system through advancements in elemental technology and full-cell engineering. RISING3 aims to develop a sealed zinc-anode rechargeable battery by developing positive electrode (cathode) materials to replace air electrodes. A notable achievement of this study is proving that the manganese dioxide (MnO₂) prepared through electrolysis (EMD) has good rechargeability in alkaline electrolyte systems, in which the amount of structural water in the oxide determines the discharge capacity for the first one-electron reduction. We also found that the newly developed MnO₂ from the chemical reduction of permanganate (PMD) enables a reversible two-electron reaction even in the electrolyte containing zinc species, in which hetaerolite (ZnMn₂O₄) generally forms to inhibit further electrochemical reactions.

This study demonstrates that the acoustic emission (AE) methodology can be successfully applied to zinc-air battery systems. AE analysis provides real-time insights into mechanically induced events and enables qualitative correlation with electrochemical processes during different operating stages. The method shows high sensitivity to corrosion-driven hydrogen evolution under open-circuit conditions and to oxygen-evolution-related activity in catalyst-based gas diffusion electrodes during charging. In commercial cells, a pronounced increase in AE activity once the cell voltage exceeds 1.8 V indicates the onset of carbon-related degradation, while final AE spikes prior to failure reflect the mechanical manifestation of critical degradation events such as separator rupture or electrode collapse. Overall, the results highlight AE as a powerful diagnostic tool for identifying degradation phenomena in metal–air batteries. Consideration of the observed diffusion limitations and the future implementation of advanced analysis tools, including distribution of relaxation times, equivalent circuit models, and machine-learning approaches, will further refine the understanding of process contributions in next-generation rechargeable battery systems.

Sodium-sulfur (Na/S) batteries are promising low-cost next-generation batteries. In particular, all-solid-state Na/S batteries are expected to demonstrate high capacity at room temperature because sulfur has a high theoretical capacity as a positive electrode active material and sulfide solid electrolytes exhibit high ionic conductivity. However, sulfur is insulating and must be mixed with conductive agents to create both ionic and electronic conductive pathways. In addition, sulfur undergoes a large volume change during cycling, and the solid-solid interface connections are easily lost. Therefore, it is necessary to devise a composite positive electrode design that achieves a high capacity by maintaining the solid-solid interface and activating sulfur redox reactions. In this study, sulfur, mesoporous carbon, and Na₃PS₄ or Na₃SbS₄ are used as composite positive electrodes, and the preparation conditions of the composite positive electrodes are investigated by charge–discharge testing and cross-sectional observations. This study clarifies that the type of sulfide solid electrolytes and its degree of dispersion in the composite electrode significantly modify electronic/ionic percolation pathways and interfacial stability, thereby governing sulfur utilization and cycling retention.