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.