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A finite element model was developed to simulate ion fluxes and local pH changes within and around porous electrodes during the H 2 evolution reaction (HER) in acidic electrolytes. This model is particularly characterized by its ability to simulate scenarios in which the local pH inside and near the cathode exceeds 7, even under bulk acidic conditions (e.g., pH = 1), by considering the self-ionization of water. Steady-state calculations using meshes with an appropriate spatial distribution inside and near the cathode revealed that the relationship between the local pH and the double-layer potential at the interface between the porous catalyst layer and the electrolyte domains changed notably when the local pH exceeded the threshold of 7. By comparing the fluxes of H + and OH - ions at the interface and using the thickness of the catalyst layer as a variable, we determined that the presence of H + ions within the pores or the supply of OH - ions from the pores to the interface was responsible for the characteristic change in the local pH observed for the porous electrode. The porous electrode model constructed in this study can potentially serve as a basis that can be extended to a wide range of electrolysis systems, including not only the HER, but also the reduction of CO 2 , H 2 O 2 , and O 2 , and even oxidation reactions such as the O 2 evolution reaction.

The electrochemical CO 2 reduction reaction (CO 2 RR) is a promising strategy for closing the carbon cycle. Increasing the current density (  J) for CO 2 RR products is a critical requirement for the social implementation of this technology. Herein, nanoscale tin-oxide-modified copper-oxide foam is hybridized with a carbon-based gas-diffusion electrode (GDE). Using the resultant electrode, the J formate is increased to -1152 mA cm -2 at -1.2 V versus RHE in 1 m KOH, which is the highest value for CO 2 -to-formate electrolysis. The formate faradaic efficiency (FE formate ) reaches ≈99% at -0.6 V versus RHE. The achievement of ultra-high-rate formate production is attributable to the following factors: i) homogeneously-modified Sn atoms suppressing H 2 evolution and ii) the hydrophobic carbon nanoparticles on GDEs penetrating the macroporous structure of the foam causing the increase in the thickness of triple-phase interface. Additionally, the FE formate remains at ≈70% under a high J of -1.0 A cm -2 for more than 20 h., (© 2022 The Authors. Small published by Wiley-VCH GmbH.)

We fabricated a thin film of layered MnO 2 whose interlayer space was occupied by hydrated Ni 2+ and Cu 2+ ions. The process consisted of electrodeposition of layered MnO 2 intercalated with tetrabutylammonium cations (TBA + ) by anodic oxidation of aqueous Mn 2+ ions in the presence of TBA + , followed by ion exchange of the initially incorporated bulkier TBA + with the denser transition metals in solution. The resulting layered MnO 2 co-intercalated with Ni 2+ and Cu 2+ ions (NiCu/MnO 2 ) catalyzed the ammonia oxidation reaction (AOR) in an alkaline electrolyte with a much lower overpotential than its Ni 2+ - and Cu 2+ -intercalated single-cation counterparts. Surprisingly, the NiCu/MnO 2 electrode achieved a faradic efficiency as high as nearly 100% (97.4%) for nitrogen evolution at a constant potential of +0.6 V vs Hg/HgO. This can be ascribed to the occurrence of the AOR in the potential region where water is stable and dimerization of the partially dehydrogenated ammonia species is preferred, thereby forming an N-N bond, rather than to be further oxidized into NO x species.