Growth of Necklace‐Like CoS ₂ Anchor on Spent Battery‐Derived Graphene Oxide Nanosheets for Stable Hydrogen Evolution Reaction: Experimental and Theoretical Insights

In this work, novel CS‐630/xSBGO composites were synthesized by anchoring three‐dimensional (3D) CoS ₂ (CS‐630) nanoparticles directly onto spent battery‐derived graphene oxide (SBGO) nanosheets through a facile pyrolysis process, forming an integrated conductive SBGO‐supported structure. The resulting CS‐630/xSBGO composites were systematically evaluated as an electrocatalyst for hydrogen evolution reaction (HER) in acidic electrolyte. Among the investigated compositions, the optimized CS‐630/0.2SBGO (1:0.2 w/w) catalyst demonstrated outstanding HER performance in 0.5 M H ₂ SO ₄ , requiring only 170 mV to reach 10 mA cm ⁻² , with a Tafel slope of 48 mV dec ⁻¹ and an exchange current density of 0.0178 mA cm ⁻² . This improved performance arises from the abundant heterointerfaces between CS‐630 and SBGO, which modulate the electronic structure, promote charge transfer, and accelerate the kinetics of water adsorption and dissociation. In addition, the conductive SBGO matrix provides a sustainable platform that highlights a waste‐to‐resource strategy for energy conversion. The catalyst also demonstrates stable HER performance in real water samples with a Faradaic efficiency of 95% under acidic conditions. Density functional theory calculations reveal pronounced electronic coupling and charge redistribution at the CoS ₂ –SBGO interface, which modulate the local electronic environment of the active sites and may contribute to the enhanced HER activity.