Harnessing in-situ electrocatalytic oxidation with a cobalt oxide decorated nanocomposite electrode for efficient arsenic removal in capacitive deionization

Limited electrocatalytic oxidation of As(III) to As(V) constrains the potential of capacitive deionization (CDI) for achieving efficient arsenic removal. In this study, we present a novel approach to incorporate cobalt oxide (CoOx) nanoparticles with activated carbon (AC), referred to as a bifunctional nanocomposite CoOx/AC electrode, and thereby achieve the simultaneous in-situ electrocatalytic oxidation of As(III) and the efficient electrosorption of As(V). The electrochemical measurements of the CoOx/AC electrode, which had a high specific surface area of 540.2 m2 g−1, demonstrated good electrical conductivity and electrocatalytic activity toward the As(III) oxidation reaction. Asymmetric CDI experiments with the CoOx/AC electrodes were performed at 1.2 V in batch-mode for different pH values. It is indicated that elevated pH can enhance the As(III) removal efficiency. Compared to the AC electrode, the CoOx/AC electrode had a considerably higher electrosorption capacity of 0.75 mg g−1 with a low energy consumption of 0.12 kWh m−3 at pH 10. To obtain insight into the mechanisms, the As(III)/As(V) concentrations and distribution were investigated in a charging–discharging cycle. When the CoOx/AC electrode was used as the anode, the electrocatalytic conversion of As(III) into As(V) was significantly enhanced from 43% to 67%, and then the generated As(V) could be electroadsorbed by electrical double-layer charging, thereby achieving an improvement in As(III) removal. Finally, the single-pass asymmetric CDI operated at ten consecutive charging–discharging cycles further demonstrated the great feasibility of using the CoOx/AC electrode to promote the in-situ electrocatalytic oxidation of As(III) for remediation of arsenic-contaminated groundwater.