Investigation of lithium cobalt oxide under oxygen evolution reaction conditions

Metal-air batteries are drawing much attention as the active material O₂ could be directly used from air. The fundamental electrochemical reactions occurring in metal-air batteries are the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which require the use of efficient catalysts to lower the overpotential and improve the efficiency. Many less expensive oxide catalysts are gaining much attention, but the mechanisms involved are still not well understood. The electrocatalytic OER performance of various forms of lithium cobalt oxide has been studied to systematically establish the surface level catalytic mechanisms. 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 the lower-temperature synthesis conditions. Raman spectroscopy, along with the presence of an irreversible peak during the first cycle of the 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.