Mechanistic Regulation by Oxygen Vacancies in Structural Evolution Promoting Electrocatalytic Water Oxidation

Introduction of oxygen vacancies (Vo) has been considered an effective strategy for promoting the oxygen evolution reaction (OER) performance of electrocatalysts. However, the role of Vo in improving OER activity is unclear. Herein, a Vo-rich spinel Co3O4 was used as a model catalyst to explore the mechanism of Vo in structural evolution during OER. The results suggest that the Vo-rich environment facilitates the reconstruction of Co3O4 to the Co(OH)2 intermediate with proton vacancies (Co(II)Ox(OH)y), which is favorable for the formation of the active species of CoOOH. Correlative operando characterizations and electrokinetic analyses indicate that a moderate Vo density can switch the O–O bond formation pathway, from a water nucleophilic attack to an intramolecular nucleophilic attack pathway, which is more kinetically favorable for water oxidation. However, a high Vo density quenches the formation of highly valent active intermediates. This study provides significant insights into the crucial role of vacancy defects during OER.