A chloride-radical-mediated electrochemical filtration system for rapid and effective transformation of ammonia to nitrogen

Abstract

Water contamination from ammonia has recently became a global concern. Herein, a chloride-radical-mediated electrochemical filtration system has been developed towards effective and rapid conversion of ammonia to nitrogen (N2). This continuous-flow system consists of a nanoscale tin oxide modified carbon nanotube (SnO2-CNT) anode and a Pd−Cu co-modified Ni foam (Pd−Cu/NF) cathode. The SnO2-CNT anode enables the Cl− oxidation to a chloride radical (Cl) at a proper anode potential (e.g., 2.5 V vs. Ag/AgCl) without severe self-oxidation. The macro-porous Pd−Cu/NF cathode further reduces anodic by-products (e.g., NO3− and NO2−) to N2. EPR and scavenging tests indicate that Cl was the dominant radical specie responsible for ammonia conversion. Anode potentials, chloride concentration, flow rate and solution pH were identified as key parameters affecting the overall conversion performance. The proposed continuous-flow system showed enhanced conversion kinetics as compared to the conventional batch reactor due to the convectively enhanced mass transport. This study provides new insight for the rational design of advanced continuous-flow systems towards ammonia decontamination from water bodies.