Recycled Co(OH)₂ from spent LiCoO₂ cathodes as a low-cost graphite-based composite electrode for the oxygen evolution reaction

Abstract The conversion of materials recovered from spent lithium-ion batteries into functional electrodes provides a promising strategy for integrating waste valorization with electrochemical energy conversion. In this work, cobalt was recovered from spent LiCoO₂ cathodes with an apparent leaching efficiency of approximately 99.7% and precipitated as Co(OH)₂ with a yield of approximately 98%. The recovered Co(OH)₂ was directly incorporated into a low-cost graphite/paraffin composite electrode for the oxygen evolution reaction (OER) in alkaline medium. The electrode containing 40 wt% Co(OH)₂ exhibited the best performance, achieving 10 mA cm⁻ 2 at an overpotential of approximately 310 mV and a Tafel slope of 75 mV dec⁻ 1 . Compared with the unmodified graphite/paraffin electrode, Co(OH)₂ incorporation increased the double-layer capacitance by approximately 8.4-fold and decreased the polarization resistance by about 72%. An apparent reaction order of 0.87 with respect to OH⁻ indicated a strong dependence of the OER kinetics on hydroxide concentration. The optimized electrode maintained a current density close to 10 mA cm⁻ 2 during 180 h of continuous operation at η = 310 mV. These results demonstrate a simple, low-cost, and potentially scalable route for converting cobalt recovered from spent Li-ion batteries into functional electrodes for alkaline water oxidation.