Fabricating Spinel-Type High-Entropy Oxides of (Co, Fe, Mn, Ni, Cr)₃O₄ for Efficient Oxygen Evolution Reaction

Fabricating efficient oxygen evolution reaction (OER) electrocatalysts is crucial for water electrocatalysis. Herein, the spinel-type high-entropy oxides of (Co, Fe, Mn, Ni, Cr)₃O₄ were synthesized through the high-temperature calcination approach. The influences of calcination temperatures on structures and electrochemical properties were investigated. The optimized catalyst of HEO-900 contains the hybrid structure of regular polyhedrons and irregular nanoparticles, which is beneficial for the exposure of electrochemically active sites. It was identified that the abundant high-valence metal species of Ni³⁺, Co³⁺, Fe³⁺, Mn⁴⁺, and Cr³⁺ are formed during the OER process, which is generally regarded as the electrochemically active sites for OER. Because of the synergistic effect of multi-metal active sites, the optimized HEO-900 catalyst indicates excellent OER activity, which needs the overpotential of 366 mV to reach the current density of 10 mA cm^-2. Moreover, HEO-900 reveals the prominent durability of running for 24 h at the current density of 10 mA cm^-2 without clear delay. Therefore, this work supplies a promising route for preparing high-performance multi-metal OER electrocatalysts for water electrocatalysis application.