The cover art is attributed to a comprehensive paper entitled “Development and Demonstration of Large-scale Alkaline Water Electrolysis System ‘Aqualyzer’” by Yasuhiro Fujita et al., selected as an Editor’s Choice. The paper presents an outstanding achievement in developing and demonstrating the large-scale alkaline water electrolysis system. Building on the company’s long-standing expertise in chlor-alkali electrolysis, the authors establish an integrated system that combines advanced cell components with sophisticated control and simulation technologies. The cover photograph features the newly constructed alkaline water electrolysis pilot test plant at Asahi Kasei’s Kawasaki Works, supported by the NEDO “Green Innovation Fund” adopted in 2021, and in operation since May 2024. Together with the 10 MW-class system at the Fukushima Hydrogen Energy Research Field (FH2R), these developments demonstrate remarkable technological maturity and industrial readiness. Furthermore, the integration of dynamic pressure control, reverse-current suppression, and simulation-based optimization for hydrogen-cost reduction exemplifies a comprehensive engineering approach that bridges materials science and system design. This paper highlights Japan’s leading contribution to the global green-hydrogen initiative and serves as an excellent reference for the future realization of 100 MW-class electrolysis plants and a sustainable hydrogen economy.

Sweat lactate monitoring has recently garnered increasing attention for assessing athlete performance, optimizing training, and determining fatigue levels. Thus, this study introduces a wireless dual-biosensor device for continuous monitoring of sweat lactate and pH. The pH sensor exhibits a sensitivity of −61 ± 0.5 mV pH⁻¹, while the lactate sensor displays a sensitivity of 0.0149 ± 0.0004 mA cm⁻² mM⁻¹ at pH 7.5. We establish a method to precisely measure lactate within the pH range of 5.5 to 7.5, taking into account the pH-dependent sensor sensitivity. The dual-biosensor device incorporates polydimethylsiloxane microfluidics for collection of sweat, its delivery to the sensor, and disposal of used sweat, enabling continuous and precise monitoring. On-body tests demonstrate the ability of the proposed device to continuously monitor sweat pH and lactate levels in individuals during exercise.

Although electrochemical methods have been used to relate microbial motility with ionic or redox signals, the evaluation of diffusion-layer variations induced by such motility using electrochemical impedance spectroscopy (EIS) remains limited. Thus, in this study, EIS is used to investigate how the flagellar activity of Volvox carteri modulates the diffusion layer above an electrode. Finite-element simulations and distributed equivalent-circuit modeling are performed for both uniform and non-uniform diffusion-layer thicknesses. Simulations predict that phototactic flagellar convection results in impedance spectra with a slope lower than 45° in the mid-frequency region and a pronounced finite-diffusion bend at low frequencies. These features are validated through experiments involving Volvox-immobilized electrodes under dark and illuminated conditions. Light irradiation reduces the effective diffusion-layer thickness from 2.4 × 10⁻² cm to 6.6 × 10⁻³ cm and introduces a distributed thickness ranging from 4.5 × 10⁻⁴ to 9.0 × 10⁻³ cm, as extracted by transmission-line fitting. These results provide quantitative insights into bio-induced mass-transport modulation and demonstrate the applicability of distributed diffusion models in bioelectrochemical systems.

Ionic liquids (ILs) are attractive electrolytes for Li metal batteries because of their non-volatility, non-flammability, and wide electrochemical stability window. Among them, 1-ethyl-3-methylimidazolium (EMI)-based ILs exhibit high ionic conductivity but suffer from limited reductive stability, and their compatibility with Li metal anodes remains insufficiently explored in the literature. Herein, we report a systematic investigation of binary mixture electrolytes with bis(fluorosulfonyl)imide (FSI) anions, [EMI][FSI]–LiFSI, for Li metal anodes. Increasing the LiFSI concentration improves the Li deposition/dissolution Coulombic efficiency through robust FSI-derived solid electrolyte interphase (SEI) formation and a positive shift in the Li deposition/dissolution potential, which together contribute to the suppression of EMI⁺ decomposition. Furthermore, solvent dilution reveals contrasting effects: coordinating dimethoxyethane (G1) weakens the Li⁺–FSI⁻ interactions and reduces the Coulombic efficiency, whereas the non-coordinating hydrofluoroether (HFE) preserves the interfacial stability while lowering the viscosity. These findings establish EMI-based ILs as a promising class of non-flammable electrolytes, providing an optimal design strategy for achieving highly reversible and safe Li metal batteries.

Titanium dioxide (TiO₂) is one of the candidates for nonplatinum electrocatalysis of the cathode of a fuel cell. Adsorbates on the electrode surface affect the activity of electrochemical reactions. However, adsorbates on TiO₂ single crystal electrodes have not been determined in electrochemical environments. In this study, we have studied the adsorbates on the low index planes of 1 % Nb-doped rutile TiO₂ single crystal electrodes (Nb/TiO₂) in 0.1 M (mol L⁻¹) HClO₄ using nanoparticle surface-enhanced Raman spectroscopy (NPSERS) and infrared reflection absorption spectroscopy (IRAS). A NPSERS band was observed on Nb/TiO₂(110) surface at 585 cm⁻¹ above 0.5 V (vs. RHE). The band was shifted 15 cm⁻¹ to lower frequency in D₂O, indicating that the corresponding adsorbed species contains hydrogen. This band was assigned to a symmetric stretching vibration of Ti–OH–Ti (bridged OH) according to the density functional theory (DFT) calculations. The onset potential of the 585 cm⁻¹ increased as Nb/TiO₂(100) < Nb/TiO₂(110) ∼ Nb/TiO₂(111). However, the order of the activity for the oxygen reduction reaction (ORR) was Nb/TiO₂(100) < Nb/TiO₂(111) < Nb/TiO₂(110). No direct correlation was found between the onset potential of the 585 cm⁻¹ band and the ORR activity. IRAS spectra found adsorbed water on Pd doped Nb/TiO₂(110) (Pd/Nb/TiO₂(110)), the most active plane for the ORR, whereas no adsorbed water was observed on Pd/Nb/TiO₂(100) that has no ORR activity. These findings suggest that adsorbed water, which is undetectable by NPSERS, may induce the ORR activity on Nb/TiO₂.

Electrochemical CO₂ reduction to multicarbon products offers a promising pathway for closing the anthropogenic carbon cycle while producing value-added chemicals. However, conventional gaseous CO₂ electrolysis suffers from severe performance losses when O₂ impurities are present. In this study, we focused on a HCO₃⁻-derived CO₂ reduction system, in which gaseous CO₂ is generated in-situ within the electrolyzer, enabling efficient formation of a three-phase interface required for high-rate C₂₊ synthesis. We have successfully achieved a faradaic efficiency of 67.4 % and a partial current density exceeding 300 mA cm⁻² for C₂₊ compounds. Importantly, the HCO₃⁻-derived CO₂RR demonstrated excellent oxygen tolerance, maintaining both the faradaic efficiency and partial current density for C₂₊ products even when CO₂ gas containing 20 % O₂ was used as the source for HCO₃⁻ solutions.

In lithium-ion batteries (LIBs), the microstructure of porous electrodes is known to significantly affect various characteristics, including charge-discharge performance, safety, and degradation behavior. Although conventional microstructural parameters such as porosity, specific surface area, average pore size and tortuosity have been employed for evaluation, the microstructural features of these complex electrodes are not necessarily fully captured by them. In this study, artificial structures that simulate electrode porosity through sphere packing were constructed, and the applicability of topological data analysis using Persistent Homology was investigated. The relationship between the extracted microstructural features and effective properties, such as effective electronic conductivity, were evaluated using a linear machine learning algorithm, and the features with high contribution were discussed. Such information could be applicable to electrode design and structural optimization.

The shift towards low-carbon hydrogen via water electrolysis using renewable electricity is crucial for reducing greenhouse gas (GHG) emissions across various industrial sectors. Asahi Kasei, a Japanese chemical company, has leveraged its extensive chlor-alkali electrolysis expertise to develop and demonstrate a large-scale alkaline water electrolysis system, the “Aqualyzer.^†” This paper provides an overview of the core technologies developed for Aqualyzer, including advanced electrolysis components, dynamic control methods, and system simulation technologies. It also details the key test and demonstration facilities, specifically the 10 MW-class system deployed at the Fukushima Hydrogen Energy Research Field (FH2R) and the alkaline water electrolysis pilot test plant comprising four modules in Kawasaki, Japan.