Preparation, characterization, and application of Cu-based catalysts in electrocatalytic reduction of nitrate: A review

Nitrate-nitrogen (NO3--N) pollution has become a major global concern because it affects the nitrogen cycle and causes risks to ecosystems and the health of mankind. Electrocatalytic reduction of nitrate (NO3RR) is notable for its high efficiency and unique advantages. In recent years, Cu-based catalysts, characterized by their costeffective, high-energy storage, and high activity, have shown excellent catalytic performance in enhancing NO3RR reactions. These include nano-copper, single-atom copper, copper oxide, cuprous oxide, copper-metal composites, and supported copper-based catalysts, all of which have widespread application in NO3RR. However, a systematic and comprehensive review of studies about the synthesis, characterization, and application of Cu-based catalysts is lacking. Therefore, in this paper, the catalytic pathway for electrocatalytic nitrate reduction to NH3 and N-2 is revealed with the help of an array of characterization techniques. A detailed review of characterization techniques and synthesis methods of Cu-based catalysts is presented. The catalytic performance of Cu-based catalysts in the NO3RR system is evaluated. The reusability of the Cu-based catalyst and the impact of the primary operational parameters (pH of the solution, current density, catalyst dosage, initial NO3--N concentration, electrolyte, etc.) in the NO3RR system are discussed. Three typical functions of density functional theory (DFT) in NO3RR systems are introduced. Finally, some opportunities and challenges for this field of study are suggested.