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.