Facile electrodeposition of nickel- and cobalt-based metal oxides as bifunctional electrocatalysts for alkaline water splitting

Abstract Herein, we demonstrated nickel- and cobalt-based metal oxide electrocatalysts were synthesized on fluorine-doped tin oxide substrates via a simple, low-cost potentiostatic electrodeposition method at room temperature and evaluated as bifunctional electrodes for alkaline water splitting. Despite their straightforward synthesis and absence of noble metals, the prepared electrodes exhibit competitive electrocatalytic activity toward both half-reactions. For the hydrogen evolution reaction (HER), the CoO/NP electrode delivered − 10 mA cm⁻² at an overpotential (η) of − 398 mV, while the NiO/NP electrode required − 427 mV and exhibited faster reaction kinetics with a lower Tafel slope of 142 mV dec⁻¹. Both electrodes maintained stable performance during 15 h of continuous operation. For the oxygen evolution reaction (OER), CoO/NP reached 10 mA cm⁻² at 1.86 V (η = 630 mV), slightly outperforming NiO/NP, which required 1.89 V (η = 660 mV), whereas NiO/NP showed more favourable OER kinetics with a lower Tafel slope of 61 mV dec⁻¹. Electrochemical impedance spectroscopy confirmed efficient interfacial charge-transfer behaviour for both electrodes. Structural and morphological analyses revealed uniformly distributed nanoparticulate oxide films providing abundant active sites for both half-reactions. The complementary HER–OER performance highlights a complementary bifunctional behaviour between the nickel- and cobalt-based oxides. Combined with good durability and a facile, scalable synthesis route, these materials represent promising low-cost electrocatalysts for sustainable hydrogen production in alkaline media.