Novel Denitrification Fuel Cell for Energy Recovery of Nitrate-N and TN Removal Based on NH4+Generation on a CNW@CF Cathode

NO3–is an undesirable environmental pollutant that causes eutrophication in aquatic ecosystems, and its pollution is difficult to eliminate because it is easily converted into NH4+instead of N2. Additionally, it is a high-energy substance. Herein, we propose a novel denitrification fuel cell to realize the chemical energy recovery of NO3–and simultaneous conversion of total nitrogen (TN) into N2based on the outstanding ability of NH4+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 NO3–to NH4+rather than to N2on the CNW@CF cathode, on which negative NO3–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, NH4+is selectively oxidized to N2by 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, NO3–completely reduces to N2, and the released chemical energy is converted into electrical energy. The results indicate that 99.9% of NO3–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.