Hydrous nickel oxyhydroxide thin films on copper foil as robust electrocatalysts for alkaline oxygen evolution

Abstract

Balancing catalytic activity and durability remains a major challenge for nickel-based oxygen evolution reaction (OER) electrodes, especially when supported on earth-abundant metals. Here, we demonstrate how the electrodeposition environment governs the structural and electrochemical evolution of nickel coatings on copper foil toward hydrous NiOOH active layers. Nickel was electrodeposited from sulfate baths at pH 3 and 4 to yield compact (Ni-Cuf-3) and hierarchically nodular (Ni-Cuf-4) films, respectively. Structural and electrochemical analyses reveal that deposition pH dictates the oxide–metal coupling and, consequently, the OER performance. Ni-Cuf-4 exhibited a lower overpotential (434 mV at 50 mA cm⁻²) and approximately tenfold higher C_dl (2.68 mF cm⁻² vs. 0.221 mF cm⁻²), corresponding to a larger density of electrochemically accessible sites. In contrast, Ni-Cuf-3 delivered a higher turnover frequency (TOF ∼1 O₂ s⁻¹ per Ni site) and superior durability (∼60 h at 800 mA cm⁻²). Impedance spectroscopy highlights distinct interfacial charge transfer characteristics arising from the different film morphology. Importantly, both electrodes achieve reduced nickel loading while suppressing copper dissolution, offering a sustainable pathway to durable, cost-effective OER catalysts.