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

• A self-supported electrode (Co 3 O 4 /CF) was prepared by needle-like Co 3 O 4 directly growing on Co foam. • The physicochemical and electrochemical characters of Co 3 O 4 /CF were regulated by calcination temperature. • Co 3 O 4 /CF had great electrochemical active surface area (ECSA) and electrons transfer efficiency. • Co 3 O 4 /CF showed high activity and selectivity for electrochemical denitrification. • Electrochemical NO 3 – reduction was induced by the Co 2+ –Co 3+ –Co 2+ redox process. Although Co 3 O 4 -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 (Co 3 O 4 /CF) was first fabricated via in-situ growth of needle-like Co 3 O 4 on the cobalt foam (CF) and then used as cathode for electrochemical denitrification. The physicochemical and electrochemical characters of Co 3 O 4 /CF could be regulated by calcination temperature. Owing to the needle-like structure and the internal contact between Co 3 O 4 and CF, the as-prepared Co 3 O 4 /CF-600 electrode exhibited excellent electrochemical performances for NO 3 – removal. The influences of current density, initial NO 3 – concentration, solution pH, and additive Cl - concentration on electrochemical NO 3 – reduction were considered. A high NO 3 – removal efficiency (72.9%) and N 2 selectivity (96.2%) were achieved by Co 3 O 4 /CF-600 electrode under the optimum conditions: current density 5 mA/cm 2 , Cl - concentration 1500 mg/L and initial NO 3 – concentration 50 mg N/L. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) confirmed that electrochemical denitrification was mainly realized via Co 2+ –Co 3+ –Co 2+ redox process instead of H*-mediated indirect process. Moreover, the Co 3 O 4 /CF electrode material could keep its electrochemical properties even after 10 cycles.