Assessment of five different cathode materials for Co(II) reduction with simultaneous hydrogen evolution in microbial electrolysis cells

Abstract

Cobalt recovery from aqueous Co(II) is one critical step for recovery of cobalt and recycle of spent lithium ion batteries, but suffers from consumption of large amount of energy and chemicals. Previous tests have primarily examined the performance of graphite felt cathode for Co(II) reduction and hydrogen production in microbial electrolysis cells (MECs). The materials of nickel foam (NF), stainless steel woven mesh (SSM), titanium sheet (TS), carbon cloth (CC), and nickel foam + graphene (NF + G) were compared here as cathodes for Co(II) reduction and hydrogen evolution in MECs. Co(II) reduction on the cathodes of TS, SSM, CC and NF + G was not significantly different from each other and increased with the increase of applied voltage from 31.8 ± 6.0% at 0.2 V to 72.2 ± 4.6% at 0.5 V, which was always higher than 16.5 ± 1.8%‒53.4 ± 2.2% on the NF cathodes at the same range of applied voltage. While a low dissolved oxygen (DO) of 1.0 mg/L benefited to both Co(II) reduction and hydrogen evolution for all the materials cathodes with generally appreciable differences from each other, cobalt produced in previous fed-batch operations improved hydrogen evolution in the subsequent batch cycles. These results provide the first assessment of these materials for Co(II) reduction with simultaneous hydrogen evolution, and SSM as the most promising inexpensive alternative to the others.