Dual-phase spinel manganese-cobalt hybrid oxide for enhanced oxygen evolution catalysis in acid media

Developing efficient and durable non-noble-metal catalysts for the oxygen evolution reaction (OER) in acidic media remains a critical challenge for proton-exchange membrane water electrolysis. Here, we report a dual-phase Mn₃O₄-Co₂MnO₄ hybrid oxide electrocatalyst synthesized via a sulfur-assisted co-electrodeposition strategy in a choline chloride/ethylene glycol-based deep eutectic solvent, followed by annealing. The incorporation of sulfur facilitates the formation of a cubic spinel Co₂MnO₄ phase within the Mn₃O₄ host, optimizing electronic conductivity and stabilizing the catalytic layer by strengthening Mn–O bonds. When supported on a corrosion-resistant Pt/Ti substrate, the composite electrode achieves a low overpotential of 317 mV at 10 mA cm⁻² and sustains stable operation for over 100 h in 0.05 M H₂SO₄ (pH = 1), outperforming most MnO_x-based catalysts and approaching noble-metal benchmarks. Density functional theory calculations reveal that the Co₂MnO₄ phase lowers the energy barrier for the rate-determining OOH* → O₂ step, while in-situ spectroscopic analyses confirm its structural integrity under acidic OER conditions. Furthermore, electrolyte dissociation kinetics significantly influences performance, with HClO₄ exhibiting superior mass transfer due to its high proton conductivity. This work provides a rational design pathway for non-noble-metal acidic OER catalysts through phase engineering and electrolyte optimization, advancing sustainable hydrogen production technologies.