Recovered spinel MnCo2O4 from spent lithium-ion batteries for enhanced electrocatalytic oxygen evolution in alkaline medium

Abstract

A facile way of recovering 3d transition metals of industrial importance from spent lithium-ion batteries (LIBs) without using any surfactants has been developed. Mn- and Co-rich spent LIBs were chosen as sustainable sources for recovering the oxides of the respective elements. The physical dismantling of Li-ion batteries, chemical leaching with 2 M acetic acid, precipitation with ammonium carbonate, hydrothermal conditioning and calcination at 650 °C led to the facile formation of spherical spinel MnCo₂O₄ with very high morphological selectivity. The obtained spherical MnCo₂O₄ was identified by various advanced characterization techniques. Detailed electrochemical characterization revealed that the recovered spheres of spinel MnCo₂O₄ were effective in catalyzing the oxygen evolution reaction (OER) in 1 M KOH and required an overpotential of 358 and 400 mV to generate a current density of 5 and 10 mA cm⁻², respectively, with a relatively low catalyst loading (0.001025 g cm⁻²). Comparative electrocatalytic studies carried out with recovered LiCoO₂, recovered Li_XMnO_X+1 and commercially available catalysts such as RuO₂ (c-RuO₂), Co₃O₄ (c-Co₃O₄) and MnO₂ (c-MnO₂) revealed that the recovered spheres of spinel MnCo₂O₄ were more effective OER catalysts than the recovered LiCoO₂, recovered Li_XMnO_X+1, c-Co₃O₄ and c-MnO₂ and exhibited comparable activity to that of c-RuO₂ with very little difference in overpotential (∼50 mV) at current densities of 5 and 10 mA cm⁻². With such a low catalyst loading, the observed electrocatalytic performance in water oxidation of a material recovered from waste is highly significant and will surely attain greater industrial importance when the recycling of spent LIBs from electronic wastes is considered.