In-situ growth of needle-like Co3O4 on cobalt foam as a self-supported cathode for electrochemical reduction of nitrate

Although Co3O4-based non-noble metal electrodes have caused wide concern in electrochemical denitrification, the electrocatalytic activity and stability of these materials are still unsatisfied. In this work, a self-supported electrode (Co3O4/CF) was first fabricated via in-situ growth of needle-like Co3O4 on the cobalt foam (CF) and then used as cathode for electrochemical denitrification. The physicochemical and electrochemical characters of Co3O4/CF could be regulated by calcination temperature. Owing to the needle-like structure and the internal contact between Co3O4 and CF, the as-prepared Co3O4/CF-600 electrode exhibited excellent electrochemical performances for NO3- removal. The influences of current density, initial NO3- concentration, solution pH, and additive Cl- concentration on electrochemical NO3- reduction were considered. A high NO3- removal efficiency (72.9%) and N2 selectivity (96.2%) were achieved by Co3O4/CF-600 electrode under the optimum conditions: current density 5 mA/cm2, Cl- concentration 1500 mg/L and initial NO3- concentration 50 mg N/L. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) confirmed that electrochemical denitrification was mainly realized via Co2+-Co3+-Co2+ redox process instead of H*-mediated indirect process. Moreover, the Co3O4/CF electrode material could keep its electrochemical properties even after 10 cycles.