Ultrathin porous nanosheet-assembled hollow cobalt nickel oxide microspheres with optimized compositions for efficient oxygen evolution reaction

Abstract

Hollow cobalt nickel oxide microspheres assembled by ultrathin porous nanosheets with tunable Co/Ni molar ratios have been successfully synthesized via a facile “self-template” method, taking solid bimetallic alkoxide microspheres as a precursor. The compositions and the sizes of the hollow cavities of cobalt nickel oxides can be easily controlled by the Co/Ni molar ratios and the size of bimetallic alkoxide microspheres, respectively. The electrochemical measurements indicate that the cobalt nickel oxide catalysts exhibit greatly enhanced oxygen evolution reaction (OER) activity in alkaline media, and Co₂–Ni₁–O microspheres with the optimal composition show the lowest overpotential (∼310 mV for 10 mA cm⁻²) and the smallest Tafel slope (57 mV per decade). This is attributed to the large electrochemically reactive surface and good charge conduction offered by the synergetic effects between their unique structural features and tunable compositions. The hollow cobalt nickel oxide microspheres may serve as promising noble-metal-free OER electrocatalysts to replace IrO_x material, and the synthetic strategy that directs structural design can be applied to prepare other multifunctional materials.