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 N-2. 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 N-2 based 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 N-2 on the CNW@CF cathode, on which negative NO3- ions can be easily adsorbed due to their doubleelectron 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 N-2 by the strong oxidation of chlorine free radicals (Cl-center dot), which originate from the reaction of chlorine ions (Cl-) by photogenerated holes (h(+)) and hydroxyl radicals (OH center dot) 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 N-2, 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.

Automated summary

This study proposes a novel denitrification fuel cell for treating nitrate-rich wastewater, which can convert NO3- into N-2 and recover chemical energy into electrical energy using a copper nanowire-modified copper foam cathode.