In Situ Spectroscopic Identification of μ-OO Bridging on Spinel Co₃O₄ Water Oxidation Electrocatalyst

The formation of μ-OO peroxide (Co-OO-Co) moieties on spinel Co₃O₄ electrocatalyst prior to the rise of the electrochemical oxygen evolution reaction (OER) current was identified by in situ spectroscopic methods. Through a combination of independent in situ X-ray absorption, grazing-angle X-ray diffraction, and Raman analysis, we observed a clear coincidence between the formation of μ-OO peroxide moieties and the rise of the anodic peak during OER. This finding implies that a chemical reaction step could be generally ignored before the onset of OER current. More importantly, the tetrahedral Co²⁺ ions in the spinel Co₃O₄ could be the vital species to initiate the formation of the μ-OO peroxide moieties.