The Restructuring-Induced CoOx Catalyst for Electrochemical Water Splitting

Restructuring is an important yet less understood phenomenon in the catalysis community. Recent studies have shown that a group of transition metal sulfide catalysts can completely or partially restructure during electrochemical reactions which then exhibit high activity even better than the best commercial standards. However, such restructuring processes and the final structures of the new catalysts are elusive, mainly due to the difficulty from the reaction-induced changes that cannot be captured by ex situ characterizations. To establish the true structure-property relationship in these in situ generated catalysts, we use multimodel operando characterizations including Raman spectroscopy, X-ray absorption spectroscopy, and X-ray reflectivity to investigate the restructuring of a representative catalyst, Co9S8, that shows better activity compared to the commercial standard RuO2 during the oxygen evolution reaction (OER), a key half reaction in water-splitting for hydrogen generation. We find that Co9S8 ultimately converts to oxide cluster (CoOx) containing six oxygen coordinated Co octahedra as the basic unit which is the true catalytic center to promote high OER activity. The density functional theory calculations verify the in situ generated CoOx consisting of edge-sharing CoO6 octahedral clusters as the actual active sites. Our results also provide insights to design other transition-metalbased materials as efficient electrocatalysts that experience a similar restructuring in OER.

Automated summary

Recent studies have shown that transition metal sulfide catalysts can restructure into oxide clusters during catalytic reactions, promoting high activity. In the case of Co9S8 catalyst, it ultimately transforms into CoOx clusters with six oxygen-coordinated Co octahedra as the true catalytic center. Multi-model operando characterizations help to uncover the true structure-property relationship in in situ generated catalysts, providing insights for designing efficient electrocatalysts based on transition metals that undergo similar restructuring in reactions like the oxygen evolution reaction.