Enhanced selective nitrate-to-nitrogen electrocatalytic reduction by CNTs doped Ni foam/Cu electrode coupled with Cl−

In this work, a Ni foam/CNTs/Cu composite electrode was prepared via the impregnation and electrodeposition methods. The electrode enhanced the total nitrogen removal and N 2 selectivity , when served as a cathode for NO 3 − -N reduction. SEM, EDS, XRD, and XPS characterization revealed that both CNTs and metallic copper were introduced onto the surface of the Ni foam substrate successfully. Besides, the LSV, CV, EIS and C dl results indicated more electrochemical active sites were in the Ni foam/CNTs/Cu electrodes than in Ni foam/Cu electrodes. Under optimal preparation conditions, the Ni foam/CNTs/Cu electrode showed N 2 selectivity of 68.89 % and nitrate removal rate of 96.75 % in 100 mg/L nitrate solution with Na 2 SO 4 as electrolyte. The selectivity of N 2 could be significantly enhanced by adding Cl − as electrolyte, and the nitrogen selectivity increased with the increase of Cl − concentration. At 1.25 g/L NaCl, the Ni foam/CNTs/Cu electrode could achieve >95 % nitrate and total nitrogen removal and close to 100 % N 2 selectivity. The N 2 selectivity of the Ni foam/CNTs/Cu electrode was 2.534 and 1.8 times of the Ni foam/Cu electrode when 0.5 g/L Na 2 SO 4 and 0.5 g/L NaCl were used as electrolytes, respectively. Consequently, to achieve the same nitrate reduction effect, the Ni foam/CNTs/Cu electrode could reduce the amount of NaCl compared with Ni foam/Cu electrode. The electrodes were tested in 6 cycles and proved to be stable. At last, a potential mechanism of nitrate‑nitrogen removal by the electrocatalytic process was suggested.