Development of a novel graphene/Co3O4 composite for hybrid capacitive deionization system

Recently, hybrid capacitive deionization devices have gathered much attention due to high ion removal capacity, rapid ion capture and excellent stability. In this study, sodium ion battery material-reduced graphene oxide/cobalt oxide (rGO/Co3O4) has been successfully synthesized and investigated as a potential cathode for hybrid capacitive deionization (HCDI) systems for the first time. The structure and morphology of rGO and rGO/Co3O4 composites have been analyzed using XRD, FT-IR, TGA and SEM. The characterization confirms the homogeneous crystal growth of Co3O4 on the rGO sheets, with rGO weight % of 9.4 (rGO/Co3O4-A) and 25.2 (rGO/Co3O4-B). The cyclic voltammetry studies indicated that the rGO/Co3O4-B electrode exhibited high specific capacitance (210 F g(-1) at 5 mV s(-1)) with redox properties. This paper also investigates the influence of initial concentration and voltage on the ion removal capacity of the rGO and rGO/Co3O4 composites. The rGO/Co3O4-B based HCDI system presents a significantly high ion removal capacity of 18.63 mg g(-1) (250 mg L-1, 1.6 V), which is 2.8 times higher than pure rGO based CDI system (6.45 mg g(-1)). Also, the rGO/Co3O4 composites exhibited excellent regeneration ability indicating its potential use in high performance CDI systems.