Enhanced Oxygen Evolution Reaction on Upcycled LiCoO ₂ via Structural Phase Transformation

Abstract The imperative for cost‐effective, robust oxygen evolution reaction (OER) electrocatalysts for green hydrogen production aligns with the pressing need to valorize the growing stream of spent lithium‐ion batteries (LIBs). Addressing this dual challenge, this study demonstrates the direct utilization of extensively cycled lithium cobalt oxide (C‐LCO) from these spent LIBs as a high‐performance OER electrocatalyst, circumventing conventional pre‐treatments. The resultant C‐LCO exhibits markedly superior OER activity and favorable reaction kinetics when compared to its pristine counterpart. This enhanced performance is attributed to synergistic modifications induced by its electrochemical history: an increased active surface area, partial surface transformation into a spinel‐like structure, significant lithium deficiency, and a higher cobalt oxidation state. Crucially, density functional theory calculations corroborate these experimental observations, identifying lithium vacancies within the surface spinel phase as pivotal. These vacancies, in turn, optimize the material's electronic structure by modulating the Co d‐band center, which leads to near‐ideal OER intermediate binding and a dramatically reduced theoretical overpotential. Consequently, this research unveils a novel, sustainable strategy to transform LIB waste into valuable OER electrocatalysts. Beyond this practical application, it offers fundamental insights into the self‐optimizing effects of electrochemical cycling, signifying a substantial advancement in repurposing spent LIBs for clean energy technologies.