Upcycled Ni-Co-Mn oxide bifunctional electrocatalyst from spent LIBs for electrochemical water splitting

Abstract

Recovering critical metals from spent lithium-ion batteries (LIBs) and upcycling them into high-value electrocatalysts for water splitting is essential for aiding circular battery manufacturing while accelerating green hydrogen (H₂) production. Here, we report a high-performance Ni-Co-Mn oxide (NCMO) electrocatalyst derived from deep eutectic solvent (DES)-recycled waste LIB cathodes for efficient electrochemical water splitting. The calcination process of the DES-based leaching residue was systematically optimized, and the optimal calcination temperature of 800 ^oC was identified for generating a highly active mixed-metal oxide phase. Comprehensive structural and chemical characterisation confirms the formation of porous nanoscale architectures with abundant oxygen vacancies and synergistic cationic interactions. The optimized NCMO-800 electrocatalyst exhibits promising bifunctional performance, with low overpotential requirements of 320 mV and 193 mV for OER and HER respectively and high durability. In-situ synchrotron FTIR microscopy reveals the formation of OOH* during OER and strong hydrogen bonding interactions during HER, elucidating the origins of bifunctional activity. Notably, the catalyst remains active and stable under saline conditions and requires only 1.79 V to reach 10 mA cm^-2 in alkaline full-cell electrolysis. This work demonstrates a sustainable and potentially scalable route to upcycle spent LIBs cathodes into efficient and robust bifunctional catalysts for water electrolysis, advancing circular economy driven green H₂ production.