Sharifi Rad A., Adjeroud N., Michel M., Roge V., Philippe A.M., Vergne C., Andersen D., Lunca-Popa P.
ACS Applied Energy Materials, vol. 9, n° 8, pp. 5169-5179, 2026
Developing platinum-free electrocatalysts with competitive kinetics requires direct control over reaction-determining steps rather than surface area alone. Here, we demonstrate that plasma-enhanced atomic layer deposition enables deterministic control of cobalt thin-film morphology, which in turn correlates with distinct hydrogen and oxygen evolution reaction pathways. By transitioning from nanoparticle-dominated growth to continuous strained films, the rate-limiting step of the hydrogen evolution reaction shifts from Volmer-limited to Heyrovsky-limited kinetics, while oxygen evolution proceeds through facilitated oxyhydroxide intermediate formation. Optimized cobalt films exhibit Tafel slopes of 88 mV dec<sup>–1</sup> for hydrogen evolution reaction (HER) and 40 mV dec<sup>–1</sup> for oxygen evolution reaction. These findings establish atomic-layer deposition as a mechanistic design tool for electrocatalysis, enabling pathway engineering at the atomic scale.
