Activating cobalt inverse spinel oxides via Fe substitution for enhanced water splitting reaction

Abstract

Owing to their expeditious kinetics and remarkable catalytic prowess, spinel oxides have attracted significant attention as promising non-precious metal electrocatalysts for oxygen evolution reaction (OER). Modulating the oxidation state of the catalytically active B site in the spinel structure is a highly potent strategy for amplifying their OER activity. Investigations into the impact of Fe doping on the oxidation state as well as the electronic configuration of Co in NiCo₂O₄ revealed the generation of Co³⁺ ions with an electron occupancy close to one in the e_g orbital, leading to an increased production of intermediate –OOH species, thereby accelerating the OER kinetics. The synergistic effect due to the optimal presence of Fe and Co in the NiCo_0.5Fe_1.5O₄ catalyst allowed the catalyst to exhibit a reduced overpotential of 310 mV at 10 mA cm⁻² with a constant current density for 22 h in the chronoamperometric study.