Upcycling of waste lithium-cobalt-oxide from spent batteries into electrocatalysts for hydrogen evolution reaction and oxygen reduction reaction: A strategy to turn the trash into treasure

Getting inspiration from the 'waste to resource' strategic theme of circular economy, herein, we present the upcycling of the critical raw material i.e. Co-containing waste cathode from spent lithium-ion batteries (LIBs) into platinum group metal-free (PGM-free) electrocatalysts for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Lithium cobalt oxide-based cathode was recovered from spent LIBs (Waste LCOd) and subsequently treated with choline chloride: citric acid 1:1 deep eutectic solvent (DES) to obtain the full degradation of the LCO-type structure and, post thermal treatments, cobalt oxide in a carbonaceous matrix (ChCl.Citric). HER and ORR activities of derived materials were investigated in alkaline media using the rotating disk electrode (RDE) and rotating ring disk electrode (RRDE), respectively. To elucidate the role of cobalt present in the derived electrocatalysts, inks were prepared by supporting the electrocatalysts with different proportions of Ketjenblack (10:90 and 50:50 ratios). Waste LCOd closely followed the electrochemical response of commercial LCO and demonstrated the least overpotential (277 mV at -10 mA cm-2) for HER with an electrode configuration of 50:50. Whereas, ChCl.Citric 50:50 outperformed the other counterparts for ORR and exhibited a remarkable onset potential of 0.85 V (vs RHE) with the least peroxide production.