Ni–Co alloy electrodeposition from the cathode powder of Ni-MH spent batteries leached with a deep eutectic solvent (reline)

Choline chloride based-deep eutectic solvents (DES), namely: choline chloride (ChCl): urea (U), reline, ChCl: glycerol (G), and ChCl: ethylene glycol (EG), ethaline, were used as leaching media for the cathode powder of spent Ni-MH batteries. It is shown that the best metal extraction was obtained with the reline DES. The resulting solution was used as electrolytic bath for the electrochemical deposition of a Ni–Co alloy onto a glassy carbon electrode (GCE). A theoretical model that involves the simultaneous presence of two contributions, to the total current density, namely: three-dimensional nucleation and diffusion-controlled growth of the bimetallic phases, and the residual water reduction on the growing surfaces of the bimetallic (Ni–Co) nuclei, was implemented for the analysis of the potentiostatic current density transients. From this analysis, the potential dependence of kinetic parameters was obtained. SEM images of the GCE, after the potentiostatic electrodeposition, showed the formation of nuclei distributed all over the substrate surface. From EDX and XRD analysis it is shown that these nuclei were composed by Ni, Co and oxygen.