Optimizing d-p Orbital Hybridization by Tuning High-Entropy Spinel Oxides for Enhanced Alkaline OER Efficiency

Abstract

The growing need for cost-effective and efficient energy conversion technologies drives the development of advanced catalysts for the oxygen evolution reaction (OER). Our research focuses on high-entropy spinel oxides (HESOs) as efficient OER electrocatalysts. Using the molten salt synthesis method, we prepared HESO nanoparticles from Fe, Ni, Co, Mn, and Zn. By adjusting the precursor ratios, we obtained equimolar (Ni0.2Fe0.2Co0.2Mn0.2Zn0.2)3O4, CoMn-rich, and NiFe-rich samples to examine compositional effects. Among these, the CoMn-rich HESO sample exhibited superior catalytic performance in 1 M KOH solution, with an overpotential of 330.1 mV at 10 mA cm−2 and a Tafel slope of 53.5 mV dec−1. Its promising long-term stability and enhanced reaction kinetics are significant. Density functional theory (DFT) calculations and experimental results indicate that the increased Co3+ species and enhanced oxygen adsorption on the CoMn-rich HESO lower the energy barrier and accelerate electron transfer, improving the reaction kinetics. The Density of states (DOS) analysis further reveals the stronger covalency of metal active site 3d and O 2p on the surface of CoMn-rich favor the absorption of oxygen species and thus improve the electrochemical performance. This work presents an effective method for HESO synthesis and opens new avenues for energy conversion research.