Surface engineering and local electron structure modulation to accelerate electroreduction of low‐concentration nitrate

Abstract

Electroreduction of low-concentration nitrate is constrained due to the competitive hydrogen evolution side reaction and sluggish reaction dynamics. Herein, we present a NiFe-layered double hydroxide featuring hydrophobicity and oxygen vacancy by in-situ electrochemical intercalation of sodium dodecylbenzene sulphonate (V_O-NiFe-LDH/CF). Different of traditional intercalation by ion-exchange method, the V_O-NiFe-LDH/CF retains the hydrophobic property of the alkyl-chains in sodium dodecylbenzene sulphonate, while the sulfonic acid functional groups inhibit the formation of surface hydroxyl groups. The introduction of oxygen vacancy induces the local electron redistribution and d-band center optimization, thereby enhancing nitrate adsorption capacity and reducing energy barrier for the rate-determining step (*NO → *NOH). In situ FTIR measurement confirms the electrochemical hydrogenation route of nitrate. The optimized V_O-NiFe-LDH/CF can realize 96.8% nitrate removal efficiency and 96% ammonia selectivity at an initial NO₃^--N concentration of 50 mg L^-1. The NO₃^--N removal rate of V_O-NiFe-LDH/CF is 2.1-fold higher than that of NiFe-LDH/CF. Furthermore, V_O-NiFe-LDH/CF has excellent practicality for practical industrial nitrate-wastewater, the total nitrogen was reduced from 114.7 mg·L^-1 to 7 mg·L^-1. The V_O-NiFe-LDH/CF shows outstanding stability and robust anti-interference performance during the long-term experiments.