Mn dopant induced high-valence Ni3+ sites and oxygen vacancies for enhanced water oxidation

Abstract

Cost effective and durable electrocatalysts are urgently required in the oxygen evolution reaction (OER), a critical process in electrochemical energy storage and conversion devices. Conventional catalysts involve the alloying of rare elements, limiting their wide applications. In this paper, Mn doped ultrathin Ni–Fe–O nanosheets are prepared and demonstrated as an efficient OER catalyst. Mn dopant induces the generation of high valence state Ni³⁺ sites and an increased oxygen vacancy concentration in the Mn–Ni–Fe–O nanosheets, thus achieving enhanced OER kinetics. Experimentation of various dopant concentrations reveals that 2 wt% Mn doping is optimal for OER catalytic performance, achieving low overpotentials of 225 mV at a current density of 10 mA cm⁻² and 297 mV at 100 mA cm⁻², respectively, a small Tafel slope of 38.2 mV dec⁻¹, and excellent stability in an alkaline medium, which is superior to pristine Ni–Fe–O nanosheets and the state-of-the-art RuO₂ catalyst.