From Elemental Metals to Synergistic Electrocatalysis: Comparative Theoretical and Experimental Insights into FeNiCoCuMo High-Entropy Alloy for the Oxygen Evolution Reaction in Alkaline Water Electrolysis

Self-supported, hot-pressed FeNiCoCuMo high-entropy alloy (HEA) electrodes were fabricated and characterized by XRD, HRTEM and EDS, confirming an FCC matrix with minor BCC phase (~1 wt%). We map redox behavior of the individual constituents (Fe, Ni, Co, Cu, Mo) and compare it with HEA to reveal solid-solution synergy (“cocktail effect”). Electrochemistry (CV/LSV/Tafel in 1.0 M KOH) and XPS show broadened redox features for HEA and Ni/Co-rich (oxy)hydroxide signatures with MoOx contributions. Triplicate electrodes (M1–M3) deliver an average η10 = 370 mV and a Tafel slope = 78 mV dec⁻¹, outperforming monometallic references and remaining competitive with literature RuO₂ Chronopotentiometry 100 h evidence stable operation; post-mortem XRD indicates a thin reconstructed surface while the bulk remains FCC-dominated. DFT supports broadened electronic states near the Fermi level and enhanced charge transfer. Overall, structure and computation link compositional disorder, surface reconstruction, and OER kinetics in a robust anode for alkaline oxygen evolution