Transition-metal based electrocatalysts: Thickness-dependent hydrogen evolution reaction performance of Ni thin film deposited by plasma-enhanced atomic layer deposition

Understanding how nanoscale thickness influences electrocatalytic behaviour is important for efficient hydrogen-production electrodes. Nickel films with controlled thicknesses were deposited by plasma-enhanced atomic layer deposition and evaluated for the hydrogen evolution reaction in alkaline electrolyte. Scanning electron microscopy and atomic force microscopy revealed a continuous nanostructured Ni layer with an approximative thickness of 7 nm after 25 ALD cycles. Kelvin probe force microscopy suggests thickness-dependent work-function variations, with higher values for thinner films. Electrochemical measurements demonstrated a strong dependence of HER performance on Ni film thickness. The thinnest film providing full surface coverage exhibited the best response, including lower charge-transfer resistance and Tafel slope compared with thinner discontinuous deposits and thicker films. These results suggest that HER behaviour is influenced by the combined effects of film continuity, roughness, thickness, charge-transfer behaviour, and electronic-state changes associated with the nanoscale morphology evolution, highlighting PE-ALD as a promising route for designing platinum-free electrodes.