Keisuke Obata

Solid/liquid interfacial interactions play an important role in electrochemical reactions when supporting electrolyte components, such as buffer anions, interact directly with catalyst surfaces. Here, we show that phosphate addition selectively suppresses the oxygen evolution reaction (OER) performance of Ni‐rich NiFeO _x electrocatalysts at pH ∼9. Operando Raman spectroscopy and Ni K‐edge X‐ray absorption near‐edge structure/extended X‐ray absorption fine structure (XANES/EXAFS) analyses suggest that phosphate decreases a high‐potential γ‐NiOOH‐like state and attenuates the associated Ni‐centered structural response. No Fe K‐edge change larger than the experimental uncertainty was resolved during OER. The current and redox response recovered immediately after phosphate was removed, demonstrating a reversible short‐term electrolyte effect. In contrast, on‐off cycling through the Ni reduction region caused progressive loss of redox charge and catalyst material, particularly for Ni‐rich compositions. These findings highlight the importance of integrated electrolyte–electrocatalyst design for improving OER performance and durability, especially under mild pH conditions.

Solid/liquid interfacial interactions play an important role in electrochemical reactions when supporting electrolyte components, such as buffer anions, interact directly with catalyst surfaces. Here, we show that phosphate addition selectively suppresses the oxygen evolution reaction (OER) performance of Ni‐rich NiFeO _x electrocatalysts at pH ∼9. Operando Raman spectroscopy and Ni K‐edge X‐ray absorption near‐edge structure/extended X‐ray absorption fine structure (XANES/EXAFS) analyses suggest that phosphate decreases a high‐potential γ‐NiOOH‐like state and attenuates the associated Ni‐centered structural response. No Fe K‐edge change larger than the experimental uncertainty was resolved during OER. The current and redox response recovered immediately after phosphate was removed, demonstrating a reversible short‐term electrolyte effect. In contrast, on‐off cycling through the Ni reduction region caused progressive loss of redox charge and catalyst material, particularly for Ni‐rich compositions. These findings highlight the importance of integrated electrolyte–electrocatalyst design for improving OER performance and durability, especially under mild pH conditions.

To realize efficient CO ₂ electroreduction, it is important to regulate “beyond catalyst” factors, including the diffusional contribution, which reflects local partial pressures of the CO ₂ reactant and the key intermediate, CO, at the three‐dimensional porous electrode under industrially relevant conditions (e.g., at current density exceeding 200 mA cm ⁻² ). Structural parameters of the catalyst layers, such as porosity, thickness, and pore size, play a decisive role in determining selectivity and CO ₂ conversion rates, as they directly control mass transport within the electrode. This study systematically investigates the impact of the mesostructure of Cu catalyst layers originating from CuO _x precursor nanoparticles with flake‐, leaf‐, and sphere‐like morphologies, as well as their combinatorial assemblies. The maximum CO ₂ conversion rate and CO ₂ electroreduction selectivity varied greatly with catalyst particle morphology and mesoscopic catalyst‐layer properties, including void architectures and pathways for gaseous molecules. Even with Cu alone, variations in electrode mesostructure substantially modulate CO ₂ mass transfer and local CO concentration, highlighting the critical role of mesoscale architecture in determining CO ₂ reduction kinetics and selectivity. Based on these insights, we developed a tandem catalyst layer to improve ethylene productivity.

The dynamic control of surface coverage in heterogeneous catalysis offers a potential pathway to access kinetic regimes unattainable under steady-state conditions. In this study, dynamic potential modulation was applied to the hydrogenation of small unsaturated carboxylic acids on Pt/C. Kinetic analysis and density functional theory (DFT) calculations identified a Horiuti–Polanyi mechanism limited by the second hydrogenation step, governed by competitive adsorption and exothermic organic binding to the Pt surface. Using square-wave modulation to kinetically decouple organic adsorption from the surface reaction, time-averaged rates at 1 Hz exceeded quasi-static and potential-averaged limits. This enhancement is hypothesized to arise from a transient enrichment mechanism, where high organic coverages formed anodically are rapidly hydrogenated at open circuit. Additionally, a shift in the hydrogen reaction order from 0.5 to 2.0 as the duty cycle decreases indicates a transition to a kinetically controlled regime, where the reaction rate is primarily dictated by hydrogen availability due to competition with hydrogen oxidation. These results demonstrate that dynamic potential modulation effectively manipulates coverages and kinetics to control thermal catalysis in non-equilibrium regimes.

We report a facile modification of Pt nanoparticles with [SiW ₉ O ₃₄ ] ¹⁰⁻ (SiW9) polyoxometalate that markedly enhances HER activity in near-neutral media (pH 9.2) via synergistic co-tuning of Pt electronic structure and particle size.

Metal-organic framework Metal–organic framework (MOF)-derived NiNC catalysts are widely explored for CO2 electroreduction; however, maintaining stable syngas production under high current density conditions remains challenging due to active-site evolution and mass transport limitations in gas diffusion electrodes. Herein, Ni-doped ZIF-8 precursors were converted into NiNC catalysts via controlled pyrolysis and integrated into gas diffusion electrodes for CO2 electroreduction in a gas-fed flow electrolyzer. By tuning the pyrolysis temperature, atomically dispersed Ni–Nx sites are preserved at 800°C, whereas higher-temperature treatment (1000°C) induces Ni aggregation and promotes hydrogen evolution. The optimized NiNC-CB-800 electrode exhibits a microcrack-refined and hierarchically porous structure, which enhances CO2 transport and stabilizes the gas–liquid–solid triple-phase boundary. As a result, stable syngas production with H2/CO ratios close to unity (~1.4) is achieved over a wide current density range of -200 to -300 mA·cm-2, with FECO of ~35–40%, a CO mass activity of ~70 mA·mg-1, and an energy efficiency of 61.3% at -200 mA·cm-2. Continuous operation at -300 mA·cm-2 is maintained for at least 4 h without abrupt performance decay. In contrast, catalysts pyrolyzed at 1000°C show dominant hydrogen evolution due to the loss of isolated Ni–Nx sites and reduced interfacial accessibility. This work demonstrates that syngas production in flow-type CO2 electroreduction is governed by the coupled effects of active-site coordination and electrode microstructure. The results provide practical design insights for gas diffusion electrodes toward more efficient and scalable CO2 utilization processes in environmental applications.

Non-extreme pH conditions enable the use of abundant elements, attracting attention for reducing electrolyzer costs. However, electrolyte engineering─specifically, optimizing buffer ion identities and concentrations─is crucial for achieving high-efficiency water electrolysis. This study focuses on the HER in a carbonate electrolyte at pH 10.5, where the participation of bicarbonate anions (HCO₃^–) in the process is essential. The overpotentials of the HER on copper–molybdenum oxide (MoO_x(Cu)) electrocatalyst were uniquely reduced by adding phosphate anions to the K-carbonate electrolyte from the low current density region to −1 A cm^–2. Electrochemical tests suggested that near-surface electrolyte cations have a significant role in facilitating the HER, which is favorable with lower amounts of hydrated cations (i.e., K⁺ and Cs⁺). HER improvement was not observed with borate and sulfate anions, highlighting the crucial role of the phosphate anion. The enhancement of HER by the phosphate additive was not observed in the absence of Cu, suggesting unique interactions among Cu, phosphate, and weakly hydrated cations. The presence of phosphate increases the double-layer capacitance, likely by inducing positive surface reconstruction for HER through Cu–phosphate interaction. Operando Raman, infrared (IR), and X-ray absorption spectroscopies consistently suggested the presence of phosphate anion adsorbates on the MoO_x(Cu) surface, which in turn attract more cations and reactant HCO₃^– to the reaction interface and boost the HER using HCO₃^– as the proton source. Density functional theory (DFT) calculations indicate the strong adsorption of phosphate species on Cu, which is associated with enhanced interaction of K⁺ with the phosphate-modified surface. These findings provide insight into electrolyte engineering, highlighting how interfacial cation–anion organization driven by adsorption may influence the rate of electrochemical reactions involving ionic reactants.