Defect-activated surface reconstruction: mechanism for triggering the oxygen evolution reaction activity of NiFe phosphide

Abstract

Nickel–iron phosphide (NiFeP) electrocatalysts have been considered as promising non-precious metal catalysts for overall water splitting (OWS). However, despite numerous reports in this field, the origin of the activity of NiFeP, especially in the oxygen evolution reaction (OER), is still poorly understood. Here, by selectively etching Zn atoms in the Zn–NiFeP precursor, designed NiFeP electrocatalysts with rich defects anchored on carbon cloth (d-NiFeP/CC) were prepared to boost reaction kinetics. The surface defects are greatly beneficial to surface reconstruction, resulting in the generation of oxyhydroxide species, which become the real catalytic active centers. Defect-activated surface reconstruction is demonstrated by in situ Raman analyses and theoretical calculations. As a result, d-NiFeP/CC has an overpotential of only 185 mV for the OER, driving a current density of 10 mA cm⁻², and maintaining stability for 100 h. For the hydrogen evolution reaction and OWS, the overpotentials are only 88 mV and 256 mV at a current density of 10 mA cm⁻², respectively. This study not only reports an effective strategy to promote the OWS activity, but also sheds light on the active origin of transition metal phosphide during the OER.