Kinetics of Active Oxide Species Derived from a Metallic Nickel Surface for Efficient Electrocatalytic Water Oxidation

Operando spectroelectrochemistry is employed to identify the electrochemical water oxidation reaction kinetics on metallic nickel in comparison with nickel oxyhydroxide. The nickel oxide on metallic nickel shows a spectroelectrochemical feature of the active species similar to the nickel oxyhydroxide during water oxidation. This amorphous oxide on the surface of metallic nickel is a crucial catalyst exhibiting a higher water oxidation activity in both rate constants and turnover frequency than the electrodeposited nickel oxyhydroxide by 3-fold for water oxidation, using a population-based rate-law analysis. These surface characterization and kinetic results reveal the underlying mechanism of the higher water oxidation efficiency of nickel oxide derived from metallic nickel than that of the electrodeposited nickel oxyhydroxide. These results also emphasize the importance of surface oxidized nickel, in terms of the structural and chemical consideration, for the optimization of electrodes toward efficient water oxidation using nickel or nickel-containing materials.