High-valence Mo doping for highly promoted water oxidation of NiFe (oxy)hydroxide

Abstract

The electronic structure regulation of transition metal NiFe (oxy)hydroxides via doping provides an effective strategy for improving the catalytic activity towards the oxygen evolution reaction (OER). Nevertheless, the underlying mechanism of high oxygen-evolving activity induced by atomistic doping is still ambiguous. Herein, this work reports high-valence Mo doped NiFe (oxy)hydroxides with enhanced oxygen evolution activity. X-ray photoelectronic spectroscopy, operando electrochemical Raman spectroscopy and density functional theory calculations were employed to elucidate their electronic modulation, surface intermediate adsorption and catalytic reaction mechanisms. The results indicate that the incorporation of Mo can stabilize the active β-NiOOH phase in NiFe (oxy)hydroxide and facilitate surface intermediate adsorption. Furthermore, the optimized trimetallic NiFeMo (oxy)hydroxide exhibits a superior OER activity, and only a 215 mV overpotential is required to achieve a catalytic current density of 10 mA cm⁻² with a small Tafel slope of 37.9 mV dec⁻¹ in an alkaline medium. This research reveals a charge offset effect induced by high-valence metal element doping that leads to remarkably enhanced OER catalytic activity and paves the way for the application of NiFeMo (oxy)hydroxides as a high-efficiency OER catalyst.