Improving C–N–FeOx Oxygen Evolution Electrocatalysts through Hydroxyl-Modulated Local Coordination Environment

Surface and near-surface engineering design of transition metal catalysts for promoting water splitting

Transition metal catalysts are widely used in the field of hydrogen production via water electrolysis. The surface state and near-surface environment of the catalysts greatly affect the efficiency of hydrogen production. Therefore, the rational design of surface engineering and near-surface engineering of transition metal catalysts can significantly improve the performance of water electrolysis. This review systematically introduces surface engineering strategies, including heteroatom doping, vacancy engineering, strain regulation, heterojunction effect, and surface reconstruction. These strategies optimize the surface electronic structure of the catalysts, expose more active sites, and promote the formation of highly active species, ultimately enhancing water electrolysis performance. Furthermore, near-surface engineering strategies, such as surface wettability, three-dimensional structure, high-curvature structure, external field assistance, and extra ion addition, are thoroughly discussed. These strategies expedite the mass transfer of reactants and gas products, improve the local chemical environment near the catalyst surface, and contribute toward achieving an industrial-level current density for overall water splitting. Finally, the key challenges faced by surface engineering and near-surface engineering of transition metal catalysts are highlighted and potential solutions are proposed. This review offers essential guidelines for the design and development of efficient transition metal catalysts for water electrolysis.

Tailored Bimetallic Ni-Sn Catalyst for Electrochemical Ammonia Oxidation to Dinitrogen with High Selectivity

Direct electrochemical ammonia oxidation reaction (eAOR) is an efficient and sustainable strategy to process wastewater containing ammonia, and it endures overoxidation and severely competitive oxygen evolution reaction (OER). Herein, we synthesized a Ni(OH)₂/SnO₂ composite catalyst by a multistep strategy and applied it to the eAOR process. Ni(OH)₂/SnO₂ exhibited a N₂-N Faradaic efficiency (FE_N2-N) of 84.2%, with a N₂ partial current density (j_N2-N) of 2.7 mA cm^-2 at 1.55 V vs reversible hydrogen electrode (RHE) in 0.5 M K₂SO₄ with 10 mM NH₃-N (pH 11). The oxophilic Sn promoted NH₃ absorption on Ni sites while suppressing the OER. As the active species, NiOOH accelerated the dimerization of intermediates (*NH₂ or *NH) to form N₂.

Improving the Oxygen Evolution Activity of Layered Double-Hydroxide via Erbium-Induced Electronic Engineering

Layered double-hydroxide (LDH) has been considered an important class of electrocatalysts for the oxygen evolution reaction (OER), but the adsorption-desorption behaviors of oxygen intermediates on its surface still remain unsatisfactory. Apart from transition-metal doping to solve this electrocatalytic problem of LDH, rare-earth (RE) species have sprung up as emerging dopants owing to their unique 4f valence-electronic configurations. Herein, the Er is chosen as a RE model to improve OER activity of LDH via constructing nickel foam supported Er-doped NiFe-LDH catalyst (Er-NiFe-LDH@NF). The optimal Er-NiFe-LDH@NF exhibits a low overpotential (191 mV at 10 mA cm^-2 ), high turnover frequency (0.588 s^-1 ), and low activation energy (36.03 kJ mol^-1 ), which are superior to Er-free sample. Electrochemical in situ Raman spectra reveal the facilitated transition of Ni-OH into Ni-OOH for promoted OER kinetics through the Er doping effect. Theoretical calculations demonstrate that the introduction of Er facilitates the spin crossover of valence electrons by optimizing the d band center of NiFe-LDH, which leads to the G_O -G_HO closer to the optimal activity of the kinetic OER volcano by balancing the bonding strength of *O and *OH. Moreover, the Er-NiFe-LDH@NF presents high practicability in electrochemical water-splitting devices with a low driving potential of and a well-extended driving period.