Preferential Co substitution on Ni sites in Ni-Fe oxide arrays enabling large-current-density alkaline oxygen evolution.

Developing low-cost and high-activity transition metal oxide electrocatalysts for an efficient oxygen evolution reaction (OER) at a large current density is highly demanded for industrial application and remains a big challenge. Herein, we report vertically aligned cobalt doped Ni-Fe based oxide (Co-NiO/Fe 2 O 3 ) arrays as a robust OER electrocatalyst via a simple method combining hydrothermal reaction with heat treatment. Density functional theory calculation and XRD Rietveld refinement reveal that Co preferentially occupies the Ni sites compared to Fe in the Ni-Fe based oxides. The electronic structures of the Co-NiO/Fe 2 O 3 could be further optimized, leading to the improvement of the intrinsic electronic conductivity and d-band center energy level and the decrease in the reaction energy barrier of the rate-determining step for the OER, thus accelerating its OER electrocatalytic activity. The Co-NiO/Fe 2 O 3 nanosheet arrays display state-of-the-art OER activities at a large current density for industrial demands among Fe-Co-Ni based oxide electrocatalysts, which only require an ultra-low overpotential of 230 mV at a high current density of 500 mA cm -2 , and exhibit superb durability at 500 mA cm -2 for at least 300 h without obvious degradation. The Co-NiO/Fe 2 O 3 nanosheet arrays also have a small Tafel slope of 33.9 mV dec -1 , demonstrating fast reaction kinetics. This work affords a simple and effective method to design and construct transition metal oxide based electrocatalysts for efficient water oxidation.