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

Decentralized electrosynthesis of hydrogen peroxide (H₂O₂) 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 H₂O. 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 (K₇HNb₆O₁₉·13H₂O) and divalent metal cations by a hydrothermal method. The optimal NiNb₂O₆ holds an H₂O₂ selectivity of 96% with the corresponding H₂O₂ 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, NiNb₂O₆ delivers H₂O₂ 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 H₂O₂ to efficiently decomposing several organic dyes. The low-cost 3d transition-metal-mediated columbite catalysts show excellent application potentials.