Highly selective electrochemical nitrate reduction using copper phosphide self-supported copper foam electrode: Performance, mechanism, and application.

A highly active and selective electrode is essential in electrochemical denitrification. Although the emerging Cu-based electrode has attracted intensive attentions in electrochemical NO reduction, the issues such as restricted activity and selectivity are still unresolved. In our work, a binder-free composite electrode (CuP/CF) was first prepared by direct growth of copper phosphide on copper foam and then applied to electrochemical NO reduction. The resulting CuP/CF electrode showed enhanced electrochemical performance for NO reduction (84.3%) with high N selectivity (98.01%) under the initial conditions of 1500 mg L Cl and 50 mg N L NO. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) demonstrated that electrochemical NO reduction was achieved through electron transfer between NO and Cu originated from CF. The in-situ grown CuP served as the bifunctional catalyst, the electron mediator or bridge to facilitate the electron-transfer for NO reduction and the stable catalyst to produce atomic H* toward NO conversion. Meanwhile, the CuP/CF remained its electrocatalytic activity even after eight cyclic experiments. Finally, a 2-stage treatment strategy, pre-oxidation by Ir-Ru/Ti anode and post-reduction by CuP/CF cathode, was designed for electrochemical chemical oxygen demand (COD) and total nitrogen (TN) removal from real wastewater.