Novel Denitrification Fuel Cell for Energy Recovery of Nitrate-N and TN Removal Based on NH 4 + Generation on a CNW@CF Cathode.

NO 3 - is an undesirable environmental pollutant that causes eutrophication in aquatic ecosystems, and its pollution is difficult to eliminate because it is easily converted into NH 4 + instead of N 2 . Additionally, it is a high-energy substance. Herein, we propose a novel denitrification fuel cell to realize the chemical energy recovery of NO 3 - and simultaneous conversion of total nitrogen (TN) into N 2 based on the outstanding ability of NH 4 + generation on a three-dimensional copper nanowire (CNW)-modified copper foam (CF) cathode (CNW@CF). The basic steps are as follows: direct and highly selective reduction of NO 3 - to NH 4 + rather than to N 2 on the CNW@CF cathode, on which negative NO 3 - ions can be easily adsorbed due to their double-electron layer structure and active hydrogen ([H]) can be generated due to a large number of catalytic active sites exposed on CNWs. Then, NH 4 + is selectively oxidized to N 2 by the strong oxidation of chlorine free radicals (Cl • ), which originate from the reaction of chlorine ions (Cl - ) by photogenerated holes (h + ) and hydroxyl radicals (OH • ) under irradiation. Then, the electrons from the oxidation on the photoanode is transferred to the cathode to form a closed loop for external power generation. Owing to the continuous redox loop, NO 3 - completely reduces to N 2 , and the released chemical energy is converted into electrical energy. The results indicate that 99.9% of NO 3 - can be removed in 90 min, and the highest yield of electrical power density reaches 0.973 mW cm -2 , of which the nitrate reduction rates on the CNW@CF cathode is 79 and 71 times higher than those on the Pt and CF cathodes, respectively. This study presents a novel and robust energy recycling concept for treating nitrate-rich wastewater.