Deep Eutectic Solvent-Assisted Electrodeposition of Dendritic FeCoNiCu Medium-Entropy Alloy for Efficient Alkaline Oxygen Evolution

Abstract Developing low-cost and durable non-noble-metal electrocatalysts for the oxygen evolution reaction (OER) is essential for efficient alkaline water electrolysis. Herein, FeCoNiCu medium-entropy alloy electrodes with tunable dendritic architectures were prepared on Cu substrates by one-step potentiostatic electrodeposition in a choline chloride–urea (ChCl–urea) deep eutectic solvent (DES). The effects of deposition potential, deposition time, and CuCl concentration on the alloy composition, morphology, and OER performance were systematically investigated. Under the optimized conditions of −1.4 V vs Ag, 2 h, and 0.2 M CuCl, a short and thick three-dimensional dendritic network was obtained. This structure provided abundant accessible catalytic sites and efficient electron-transport pathways. The optimized FeCoNiCu electrode required an overpotential of 285 mV (corresponding to 1.515 V vs RHE) to reach 10 mA cm–2 in 1 M KOH, which was 107 mV lower than that of a commercial RuO2–IrO2 catalyst under the same evaluation conditions. The electrode also showed favorable charge-transfer kinetics, with an Rct of 2.183 Ω cm2, and maintained stable activity during a 120 h chronopotentiometric test and 2000 CV cycles. Post-OER XPS analysis suggests that Fe, Co, and Ni were reconstructed into oxide/oxyhydroxide-rich catalytically relevant oxyhydroxide-rich species, whereas Cu was less extensively oxidized and may contribute mainly to electrical conductivity and structural stabilization. This work provides a DES-assisted electrodeposition strategy for designing macroscopically homogeneous dendritic medium-entropy alloy electrocatalysts for alkaline OER.