Efficient electrocatalytic nitrate reduction in neutral medium by Cu/CoP/NF composite cathode coupled with Ir-Ru/Ti anode

Abstract

In this work, a three-dimensional self-supporting copper/cobalt phosphide/nickel foam (Co/CoP/NF) composite was fabricated and employed as the cathode for electrochemical nitrate removal from surface water with the assistance of a commercial Ir-Ru/Ti anode. The experimental results demonstrate that the introduction of Cu nanoparticles on CoP nanosheets is favorable for the electrocatalytic nitrate reduction. The influences of operating parameters (pH value, current density and initial nitrate concentration) on the nitrate reduction were assessed with the presence of Cl^-. At the optimized conditions, the removal of nitrate exhibits an efficiency ca. 100% via the coupling electrochemical reduction and oxidation processes. Moreover, the nitrogen selectivity is found to be as high as 98.8% within 210 min, accompanied with a promising test endurance (>94.0% for total nitrogen (TN) and NO₃^- removal efficiencies after an electrochemical run of 24.5 h). Importantly, as for the treated actual surface water, the concentration of TN is smaller than 1.5 mg L^-1, in accordance with the limit of Ⅳ-level standard of the surface water environmental quality in China (GB 3838-2002). The efficient removal of nitrate can be attributed to the synergistic effect of Cu and CoP microparticles to enhance the reduction activity, as well as the subsequent chloride oxidation for the major intermediate of ammonium.

Keywords: Coupling electrochemical process; Cu/CoP/NF cathode; Electrochemical denitrification; Nitrate removal; Reduction conversion.