Thin films of Ni and Co mixed metal oxides via ozone-based atomic layer deposition for bifunctional alkaline water splitting

The development of efficient and cost-effective electrocatalysts for alkaline water splitting is essential for sustainable hydrogen production. In this study, we employed atomic layer deposition (ALD) to grow Ni and Co oxide thin films, arranged either as a film stacking or codeposited in a single mixed layer, to explore how the atomic-scale arrangement of the two oxides affects the electrocatalytic performance. The films were conformally deposited onto three-dimensional Ni foam (NF) and stainless steel (SS) mesh substrates to investigate the influence of electrode architecture on electrochemical performance. Structural and morphological characterization confirmed uniform film growth and a well-controlled composition. The codeposition of nickel and cobalt oxides in a mixed metal oxide (MMO) layer outperformed the film stacking. The MMO layer deposited on SS mesh exhibited superior oxygen evolution reaction (OER) performance, while the corresponding on NF showed enhanced hydrogen evolution reaction (HER) activity with good electrochemical stability under continuous operation. The results demonstrate that catalyst architecture and substrate selection are equally important design parameters as catalyst composition for ALD-engineered bifunctional Ni–Co oxide electrocatalysts.