Evidence of Localized Lithium Removal in Layered and Lithiated Spinel Li_1–<i>x</i>CoO₂ (0 ≤ <i>x</i> ≤ 0.9) under Oxygen Evolution Reaction Conditions

Abstract

The electrocatalytic oxygen evolution reaction performance of various forms of lithium cobalt oxide has been studied to systematically establish the surface-level catalytic mechanism. The low-temperature lithiated spinel form of LiCoO₂ (designated as LT-LiCoO₂) exhibits lower overpotentials than the high-temperature layered form of LiCoO₂ (designated as HT-LiCoO₂), but this is shown to be a result of the increased surface area afforded by lower-temperature synthesis conditions. Raman spectroscopy, along with the presence of an irreversible peak during the first cycle of the oxygen evolution reaction (OER), demonstrates that the mechanism for OER is the same for both the forms of LiCoO₂. At the surface level, lithium is removed during the first cycle of the OER, forming Co₃O₄ on the surface, which is likely the active site during the OER. This work highlights the importance of determining the nature of the catalyst surface when investigating the electrocatalytic properties of bulk materials