Abstract: Self-supported, hot-pressed FeNiCoCuMo high-entropy alloy (HEA) electrodes were fabricated and characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and energy dispersive spectroscopy (EDS), confirming a face-centered cubic (FCC) matrix with minor body-centered cubic (BCC) phase (~1 wt%). We map the redox behavior of the individual constituents (Fe, Ni, Co, Cu, and Mo) and compare it with HEA to reveal solid-solution synergy (“cocktail effect”). Electrochemistry (cyclic voltammetry (CV)/linear sweep voltammetry (LSV)/Tafel in 1.0 M KOH) and X-ray photoelectron spectroscopy (XPS) show broadened redox features for HEA and Ni/Co-rich (oxy)hydroxide signatures with MoO_x contributions. Triplicate electrodes (M1–M3) deliver an average overpotential of 370 mV at 10 mA·cm⁻² and a Tafel slope of 78 mV·dec⁻¹, outperforming monometallic references and remaining competitive with the literature-reported RuO₂. Chronopotentiometry 100 h evidence stable operation; post-mortem XRD indicates a thin reconstructed surface while the bulk remains FCC-dominated. Density functional theory (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.