Unlocking the Cu-Co Interplay: Electrodeposited Spinel Co₂CuO₄ as a High-Performance Hydrogen Evolution Catalyst

Developing cost-effective and durable electrocatalysts with high hydrogen evolution efficiency remains a critical challenge for sustainable energy conversion. Herein, spinel-type Co₂CuO₄ and Co₃O₄ nanosheet electrodes were fabricated directly on Ni foam via a simple electrodeposition route and evaluated for the alkaline hydrogen evolution reaction (HER) in 1.0 M KOH. Structural and surface analyses confirmed the formation of phase-pure, porous, and highly interconnected nanosheet architectures, where the substitution of Cu²⁺ into the Co₃O₄ lattice induced charge-redistribution and optimized the electronic configuration. The Co₂CuO₄ catalyst exhibited superior activity, requiring an overpotential of 127 mV to achieve 10 mA cm^-2 with a corresponding Tafel slope of 61 mV dec^-1, outperforming the Co₃O₄ catalyst (176 mV and 95 mV dec^-1). This enhancement arises from improved intrinsic kinetics, higher turnover frequency, and reduced charge-transfer resistance, reflecting an increased density of active sites and enhanced interfacial conductivity. Furthermore, the Co₂CuO₄ catalyst maintained excellent stability for 100 h at both 10 and 500 mA cm^-2, attributed to its strong adhesion and open nanosheet framework, which facilitates efficient gas release and electrolyte diffusion. These findings establish Co₂CuO₄ as a promising and durable HER electrocatalyst for alkaline water electrolysis.