Cobalt Electrochemical Recovery from Lithium Cobalt Oxides in Deep Eutectic Choline Chloride+Urea Solvents.

Electrochemical recovery of the cobalt in deep eutectic solvent shows its promise in recycling and recovery of valuable elements from the spent lithium-ion battery due to its high selectivity and minimal environmental impacts. This work unveiled the roles of the substrates, applied potentials, and operating temperatures on the performance of cobalt electrochemical recovery in a deep eutectic choline chloride+urea solvent. The solvent contains cobalt and lithium ions extracted from lithium cobalt oxides - 3an essential lithium-ion battery cathode material. Our results highlight that the substrate predetermines the cobalt recovery modes via substrate-cobalt interactions, which could be predicted by the cobalt surface segregation energies and crystallographic misfits. We also show that a moderate cathode potential under -1.0 V vs. silver quasi-reference electrode at 94-104 °C is essential to ensure a selective cobalt recovery at an optimal rate. We also found that the stainless-steel mesh is an optimal substrate for cobalt recovery due to its relatively high selectivity, fast recovery rate, and easy cobalt collection. Our work provides new insights on metal recovery in deep eutectic solvents and offers a new avenue to control the metal electrodeposition modes via modulation of substrate compositions and crystal structures.

Understanding the Effects of Anion Interactions with Ag Electrodes on Electrochemical CO2 Reduction in Choline Halide Electrolytes.

Interactions of electrolyte ions at electrocatalyst surfaces influence the selectivity of electrochemical CO2 reduction (CO2 R) to chemical feedstocks like CO. We investigated the effects of anion type in aqueous choline halide solutions (ChCl, ChBr, and ChI) on the selectivity of CO2 R to CO over an Ag foil cathode. Using an H-type cell, we observed that halide-specific adsorption at the Ag surface limits CO faradaic efficiency (FECO ) at potentials more positive than -1.0 V vs. reversible hydrogen electrode (RHE). At these conditions, FECO increased from I- 90 %) in ChCl (at -0.75±0.06 Vvs. RHE) and ChI (at -0.78±0.17 V vs. RHE) could be achieved at a current density of 150 mA cm-2 in a continuous flow-cell electrolyser with Ag nanoparticles on a commercial gas diffusion electrode. This study provides new insights to understand the interactions of anions with catalysts and offers a new method to modify electrocatalyst surfaces.