Electrocatalytic reduction of nitrate by Cu valence-regulated heterojunction electrode: A key role of Cu(I/II) composites and high nitrate reduction efficiency

Cu - based composite electrode has aroused great concern among NO3-reduction. There are few reports on the synergistic effect of different Cu valence states. It is not clear how to regulate the valence ratio of copper by or controlling the dosage of reducing agent in the synthesis process. Herein, a Cu(I) and Cu(II) heterogeneous electrode with different Cu valences was prepared to build a Cu(I/II)@NF-UX composite electrode on nickel foam. Urea was used as a gentle reductant to construct the heterogeneous structure of Cu(I) and Cu(II) during a one-step hydrothermal process for in - situ growth of Cu(I/II)@NF-UX, and the ratio between Cu(I) and Cu(II) and the microstructure were adjusted by changing the amount of urea added during the preparation process. The strong NO3-adsorption effect of traditional Cu - based electrode is still maintained in the Cu(I/II)@NF composite. The strong interfacial electric field constructed in the Cu(I/II) heterostructure efficiently promoted the electron transfer, and the electrons subsequently reduced the NO3- directly or helped form the atomic H* for NO3- indirect reduction. More importantly, there is almost no accumulation of NO2- and NH4+, efficient and stable nitrate reduction (93.2 %) was achieved and 96.2 % N2 selectivity was achieved with the help of electric chlorination. It is worth noting that the high pH adaptability, low energy consumption, good stability, and low Cu/Ni leaching would make the Cu(I/II)@NF composite electrode have an excellent application prospect for NO3-removal engineering.