Integration of active nickel oxide clusters by amino acids for water oxidation

The move toward sustainable hydrogen production from water using renewable energy, a highly efficient oxygen evolution electrocatalyst, is crucial because watersplitting efficiency is restricted to the oxygen evolution capability, which is insufficient compared to the hydrogen evolution reaction. Herein, we report a new method that improves the oxygen evolution activity by integration of active nickel oxide clusters using amino acids, meaning that the amount of electrodeposited nickel oxides is increasing with maintaining the catalytic activity. This method enhances the catalytic activity because the reaction sites drastically increase in three dimensions. The detailed reaction mechanism was investigated using operando UV/vis absorption and Ni K-edge X-ray absorption spectroscopic techniques, which suggested that amino acids such as glycine, alanine, and glutamine promoted the electrodeposition of NiO6 octahedral structure clusters. Meanwhile, the analysis of N and O K-edge X-ray absorption spectra showed that the amino acid (glycine) in the nickel electrocatalyst was present in the molecular state. Therefore, it was spectroscopically demonstrated that amino acids are bound to nickel oxide clusters accompanied by oxygen evolution activity.