Insight into the efficient electrochemical reduction of nitrate employing Pd/Ru bimetallic doped copper foam cathode: Selectivity and reliability

Abstract

Nitrate pollution threatens ecological environment and human health. Electrochemical reduction of nitrate to ammonia using metal-doped modified cathode is a promising technique for nitrate removal. In this work, a bimetallic Ru/Pd-doped Cu foam (CF) electrode was developed for nitrate reduction using cation exchange method. Confirmed by various physio-chemical characterization, it was found that the Ru/Pd-Cu Spongy Copper Foam (SCF) was successfully prepared. In addition, nearly 100 % nitrate removal, 94.07 % NH3 selectivity, and 84.9 % Faradaic efficiency (FE) could be achieved, under the optimized conditions as 100 mg L−1 of initial NO3--N concentration, 0.3 mol L−1 of Na2SO4 as electrolyte and the applied current of 5.42 mA cm−2. Through electrochemical testing and DFT calculation, it was revealed that the bimetallic doping of Ru/Pd facilitate electrocatalytic nitrate reduction reaction (NO3RR) by reducing the energy barriers of the NO3--to-NH3 pathway from 0.81 to 0.56 eV. Besides, the electrode showed excellent stability and anti-toxicity even after 10 repeated NO3RR cycles, since the NH3 yield rate and NH3 selectivity ranged from 0.206 to 0.231 mg h−1 cm−2, 87–96.87 % respectively. After NO3RR, an extended electrochemical oxidation process was implemented to remove ammonia, and nearly 100 % of NH3 was oxidized to N2 without byproducts. Thereby, this study provides a new option for the electrochemical reduction of nitrate to ammonia via cathode modification, to achieve the substantial nitrate removal from nitrate-containing water.