Recycling cobalt in spent lithium-ion batteries for designing the hierarchically porous Co3O4/Co/CP by electrodeposition: Towards efficient overall water splitting

The recovery of valuable cobalt (Co) metal from lithium-ion batteries (LIBs), when combined with advanced synthesis techniques, presents a promising strategy for the development of high-efficiency and low-cost electrocatalysts, thereby enhancing the performance of water splitting reactions. In this study, novel 3D hierarchically porous structures composed of stacked 2D porous nanosheets (denoted as Co 3 O 4 /Co/CP) are synthesized utilizing Co resources recovered from spent LIBs. The Co 3 O 4 /Co/CP 4 h catalyst exhibits an oxygen evolution reaction (OER) potential of 1.554 V vs. reversible hydrogen electrode (RHE) at 10 mA cm −2 ( E 10 ), which is 81 mV lower than that of RuO 2 (1.635 V vs. RHE). In two-electrode configuration, the Co 3 O 4 /Co/CP 4 h nanosheets based electrolyzer achieves 10 mA cm −2 at a cell voltage of 1.63 V, representing a 60 mV improvement over the 20 wt% Pt/C||RuO₂ benchmark system. The highly porous architecture of the Co 3 O 4 /Co/CP 4 h nanosheets facilitates enhanced exposure of active sites and promotes efficient mass transport. The in-situ Raman spectroscopy confirms surface reconstructions during OER, with the formation of abundant electrochemically active CoOOH species, thereby significantly enhances the reaction kinetics. The in-situ EIS results reveal the efficient electron and mass transfer capabilities, which arise from the synergistic interaction between the highly conductive Co and the abundant porous channels within the well-defined nanosheet architecture. This study successfully demonstrates an innovative industrial chain that recycles Co from spent LIBs to fabricate high-efficiency and lost-cost HER/OER electrocatalysts. This approach not only promotes the efficient utilization of Co in spent devices but also accelerates the commercialization of hydrogen production through water electrolysis.