Electrocatalytic reduction of nitrate in water using Cu/Pd modified Ni foam cathode: High nitrate removal efficiency and N2-selectivity

Electrocatalytic reduction of nitrate is a promising technology for nitrate removal from groundwater or surface water to eliminate the negative influence on human. The activity of an electrode usually depends on many factors such as catalytic metal, accessible active centers and electrode geometry. In this work, we prepared Cu/Pd modified nickel foam electrode (NF-Cu/Pd) according to two-step electrodeposition method using nickel foam (NF) as substrate. Cu/Pd particles with a grape-cluster-like shape with pores around 100 nm between clusters were formed on the NF surface according to the field emission scanning electron microscope with energy dispersive spectroscopy (FESEM-EDS) results. The crystal structure and the valence state of the prepared NF-Cu/Pd electrode were analyzed by using powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) technology. Linear sweep voltammetry (LSV) tests indicated that the prepared NF-Cu/Pd electrode had high electrocatalytic activity for nitrate reduction either using Na2SO4 as electrolyte or using NaCl as electrolyte. According to the dynamic experiment, 97% of the initial 100 mg/L NO3–-N were removed with a N2-selectivity of 99% at the cathode potential of −1.2 V vs. Ag/AgCl (sat. KCl) when using 0.05 M Na2SO4 as electrolyte. Using NaCl as electrolyte could improve the N2-selectivity of the nitrate electrocatalytic reaction under general conditions. The cathode potential and the current density affects the reaction pathways of nitrate reduction. In the microenvironment around the active sites, the mole ratio of NO2– and Had dominated the main product of NO3– reduction. Long time cyclic voltammetry test indicated that the prepared NF-Cu/Pd electrode has a good long-term electroactive stability for nitrate reduction from water solution. And the prepared NF-Cu/Pd showed high nitrate removal efficiency (96.4%) and N2-selectivity (65.4%) from the municipal wastewater treatment plant (WWTP) effluent.