Sustainable synthesis of Ni-doped Co3O4/graphene from recycled cobalt for efficient oxygen evolution reaction.

Developing sustainable and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is essential for efficient water splitting. Herein, Ni-doped Co3O4 supported on graphene (Ni-Co3O4@G) is synthesized using cobalt recovered from spent lithium-ion batteries via a hydrothermal-calcination approach. The composite exhibits a hierarchical porous structure with uniformly dispersed nanoparticles on conductive graphene sheets, providing abundant active sites and enhanced charge transfer. XPS analysis confirms mixed valence states (Co²⁺/Co³⁺ and Ni²⁺/Ni³⁺) and rich oxygen defects, contributing to improved catalytic activity. Electrochemical results in alkaline media show that Ni-Co3O4@G achieves superior OER performance, delivering a low overpotential (1.66 V vs. RHE at 10 mA cm⁻²), a small Tafel slope (107.52 mV dec⁻¹), and excellent stability over 3000 cycles. This work demonstrates a green strategy for converting recycled cobalt into efficient OER electrocatalysts for sustainable hydrogen production.