An ultrathin defect-rich nickel–cobalt oxide nanosheet array for enhanced bifunctional oxygen electrocatalysis

Abstract

Developing transition metal oxides (TMOs) as electrocatalysts with high bifunctional activity is of significance for reversible fuel cells and rechargeable metal air batteries. Herein, we report a bifunctional nitrogen-doped NiCoO_x nanosheet array, which can stably catalyze the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). The nanosheet has an ultrathin thickness of 1–3 nm and mesoporous structure, which are favorable for the exposure of active sites. Moreover, the nanosheet has pronounced crystalline distortions as revealed by means of X-ray absorption fine structure analysis. The distortions yield an abundance of catalytically active defects (e.g. oxygen vacancies), thereby giving rise to enhanced electrocatalytic performance. The nanosheet array exhibits an ultra-small overpotential of only 239 mV at 10 mA cm⁻² for the OER and a low overpotential of 382 mV at 10 mA cm⁻² for the ORR, which places it as being one of the most active bifunctional oxygen electrocatalysts. The assembled Zn–air battery shows excellent cycling stability over 200 h during consecutive charge (OER) and discharge (ORR) processes.