3d Transition-Metal-Mediated Columbite Nanocatalysts for Decentralized Electrosynthesis of Hydrogen Peroxide

Decentralized electrosynthesis of hydrogen peroxide (H₂ O₂ ) via oxygen reduction reaction (ORR) can enable applications in disinfection control, pulping and textile bleaching, wastewater treatment, and renewable energy storage. Transition metal oxides are usually not efficient catalysts because they are more selective to produce H₂ O. Here, it is shown that divalent 3d transition metal cations (Mn, Fe, Co, Ni, and Cu) can control the catalytic activity and selectivity of columbite nanoparticles. They are synthesized using polyoxoniobate (K₇ HNb₆ O₁₉ ·13H₂ O) and divalent metal cations by a hydrothermal method. The optimal NiNb₂ O₆ holds an H₂ O₂ selectivity of 96% with the corresponding H₂ O₂ Faradaic efficiency of 92% in a wide potential window from 0.2 to 0.6 V in alkaline electrolyte, superior to other transition metal oxide catalysts. Ex situ X-ray photoelectron and operando Fourier-transformed infrared spectroscopic studies, together with density functional theory calculations, reveal that 3d transition metals shift the d-band center of catalytically active surface Nb atoms and change their interactions with ORR intermediates. In an application demonstration, NiNb₂ O₆ delivers H₂ O₂ productivity up to 1 mol_H2O2 g_cat ^-1 h^-1 in an H-shaped electrolyzer and can yield catholytes containing 300 × 10^-3 m H₂ O₂ to efficiently decomposing several organic dyes. The low-cost 3d transition-metal-mediated columbite catalysts show excellent application potentials.