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

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.