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 NO3- reduction, the issues such as restricted activity and selectivity are still unresolved. In our work, a binder-free composite electrode (Cu3P/CF) was first prepared by direct growth of copper phosphide on copper foam and then applied to electrochemical NO3- reduction. The resulting Cu3P/CF electrode showed enhanced electrochemical performance for NO3- reduction (84.3%) with high N2 selectivity (98.01%) under the initial conditions of 1500 mg L-1 Cl- and 50 mg N L-1 NO3-. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) demonstrated that electrochemical NO3- reduction was achieved through electron transfer between NO3- and Cu0 originated from CF. The in-situ grown Cu3P served as the bifunctional catalyst, the electron mediator or bridge to facilitate the electron-transfer for NO3- reduction and the stable catalyst to produce atomic H* toward NO2- conversion. Meanwhile, the Cu3P/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 Cu3P/CF cathode, was designed for electrochemical chemical oxygen demand (COD) and total nitrogen (TN) removal from real wastewater.

Electrochemical Cr(VI) removal from aqueous media using titanium as anode: Simultaneous indirect electrochemical reduction of Cr(VI) and in-situ precipitation of Cr(III).

In this work, a novel method for complete Cr(Ⅵ) removal was achieved in a single-chamber cell with titanium (Ti) as anode via simultaneous indirect electro-reduction of Cr(Ⅵ) and in-situ precipitation of Cr(Ⅲ). The Cr(Ⅵ) and total Cr removal, and electric energy consumption were optimized as a function of electrochemical reactor, current density, initial Cr(Ⅵ) and chloride (Cl-) concentration, and initial solution pH. The maximum Cr(Ⅵ) and total Cr removal efficiency reached 80.5 and 79.4% respectively within 12 h at current density of 10 mA cm-2 as initial Cr(Ⅵ) concentration was 0.078 mM. Decreasing the initial solution pH was beneficial to Cr(Ⅵ) reduction, but Cr(Ⅲ) precipitation was inhibited, resulting in the poor total Cr removal. The suitable Cl- concentration guaranteed sufficient reducing agents (Ti3+ and Ti2+) for Cr(Ⅵ) removal. The reaction mechanism demonstrated that Ti anode could be corroded to produce Ti3+ and Ti2+, which provided the electrons for reduction of Cr(Ⅵ) to Cr(Ⅲ). Simultaneously, the solid products (Ti2O(6x-y-z+52)Cl2yCr2x(OH)2z(s)) were in-situ formed and precipitated from the solution due to the continuous generation of hydroxyl ion (OH-) from cathode. This study might provide a new electrochemical method with non-precious metal as the electrode for complete Cr(Ⅵ) removal from aqueous media.