Many lives of cobalt within electrochemical systems: from waste batteries to efficient hydrogen evolution reaction electrocatalyst

The presence of critical raw materials, primarily cobalt, in scrap and spent lithium-ion batteries (LIBs) constitutes an important research spot for the recycling of LIBs and cobalt recovery. Instead of solely relying on the complicated and suboptimal application of the recovered cobalt in the fabrication of the LIB cathode materials, alternative technologies can also be explored such as alkaline water electrolysis where hydrogen evolution reaction (HER) is one of the key bottlenecks. Therefore, herein a flexible and highly efficient use of Co-based materials derived from different life stages of LIBs (from production scrap, waste cathode from spent LIBs, scraps from resynthesized cathodes) have been exploited for HER in alkaline media. Particularly, production scraps from commercial lithium cobalt oxide (c-LCO), commercial scraps LCO subjected to thermal treatment (p-LCO) at three diverse temperatures (400 °C, 550 °C and 700 °C), LCO recovered from waste batteries (w-LCO), and resynthesized LCO (r-LCO) subjected to the optimum temperature identified in the p-LCO step. The structures, morphologies, and surface chemistries of obtained materials were thoroughly analyzed and compared. Furthermore, the electrocatalyst inks were optimized by mixing with two different types of carbon substrates i.e. Ketjenblack and Vulcan XC72R in varying ratios. The half-cell measurements based on a rotating disk electrode (RDE) demonstrated encouraging HER activity with overpotentials in the range of 262–347 mV at the typical current density of 10 mA cm^− 2. This work underlines novel possibilities in the valorization of waste materials, transforming waste into value-added products by combining the ambitions of the circular economy and green energy while following simpler pathways.