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 molH2O2 gcat-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.