From elemental metals to synergistic electrocatalysis: Comparative theoretical and experimental insights into FeNiCoCuMo high-entropy alloy for alkaline oxygen evolution reaction

• FeNiCoCuMo HEA electrodes achieve 370 mV overpotential at 10 mA·cm−2 with a Tafel slope of 78 mV·dec−1 in 1.0 M KOH, outperforming monometallic references and rivaling RuO2. • Synergistic 'cocktail effect' confirmed by broadened redox features and Ni/Co-rich (oxy)hydroxide/MoOx surface signatures, linking compositional disorder to enhanced OER kinetics. • DFT calculations reveal broadened electronic states near the Fermi level and improved charge transfer, providing mechanistic insight into the HEA's high activity. • 100-hour chronopotentiometry and post-mortem XRD demonstrate stable operation with a thin reconstructed surface while preserving the FCC-dominant bulk.