Co(OH) ₂ vs. CoOOH: understanding the origin of in‐situ converted catalyst’s high catalytic activity towards oxygen evolution reaction

Abstract Metal oxohydroxides (MOOH) are widely accepted as the true active species for oxygen evolution reaction (OER). However, the MOOH converted from pre‐catalysts usually exhibits better catalytic performance than those directly synthesized. The underlying structural reason for this phenomenon remains controversial. In this work, CoOOH and Co(OH) 2 with similar morphology are employed as model catalysts to investigate the origin of in‐situ converted catalyst’s high activity, as Co(OH) 2 can be fully converted to CoOOH during OER. In‐situ Raman, electron paramagnetic resonance, HR‐TEM, and X‐ray spectroscopic studies reveal that O vacancies in the CoOOH converted from Co(OH) 2 play a key role in its higher intrinsic activity towards OER than directly synthesized CoOOH. Furthermore, theoretical calculations and electrochemical methods indicate that O vacancies in CoOOH affect the interaction between Co–O bond, downshift the d‐band center of Co, further weaken the adsorption of OH*, and finally facilitate the OER process over CoOOH. This work not only provides a deep understanding of pre‐catalyst’s high OER activity by taking Co(OH) 2 as an example but also deliver insights into the activation process of other electrochemical oxidation reactions.