Boron-Incorporated Cobalt–Nickel Oxide Nanosheets for Electrochemical Oxygen Evolution Reaction

The composition and crystal structure are crucial parameters for the activity and stability of the electrocatalysts. Herein, we synthesize a series of CoxNi–B oxide nanosheets with low degree of crystallinity for alkaline media oxygen evolution reaction (OER). The sample with an optimized ratio Co8Ni–B oxide shows the best OER performance, achieving a current density of 10 mA/cm2 at an overpotential of 312 mV and a Tafel slope of 47 mV/dec in the 1 M KOH electrolyte. This sample is stable in the purified Fe-free KOH electrolyte and strongly activated in the nonpurified commercial electrolyte due to the Fe impurity uptake. The high surface area and partially crystalline structure caused by boron incorporation and low-temperature treatment provide more accessible active sites with retaining good stability against leaching during the OER. In situ electrochemical Raman spectroscopy investigation reveals the formation of OER active Co and Ni oxyhydroxides in Co8Ni–B oxides under a potential bias. The Ni substitution in Co oxides modulates the electronic structure of Co, and the OER activity of the electrocatalyst can be enhanced by Fe uptake from the KOH electrolyte.