Recent Advances of Cu-Based Materials for Electrochemical Nitrate Reduction to Ammonia

The pollution of nitrate in groundwater has become an environmental problem of general concern due to adverse human and ecological impacts. Treatment of nitrate-rich wastewater is of significance yet challenging for the conventional biological denitrification processes. Electrocatalytic nitrate-to-ammonia conversion emerges as one of the most promising avenues to remove environmentally harmful nitrate from various types of wastewaters while simultaneously producing value-added ammonia. Cu-based materials show great advantages in promoting selective electroreduction of nitrate to ammonia in terms of high nitrate conversion efficiency, ammonia selectivity and ammonia faradaic efficiency thanks to the 3d transition metal structure, low cost, high reserves, and excellent catalytic performance of Cu. In this review, we comprehensively overview the most recent advances in selective electrocatalytic nitrate-to-ammonia conversion using Cu-based materials. Various kinds of Cu-based materials including monometallic Cu catalysts, bimetallic Cu-based catalysts, Cu-based compounds, and Cu-based inorganicorganic hybrid materials and their derivatives are discussed in detail with emphasis on their structural and compositional features and functional mechanisms in promoting nitrate-to-ammonia conversion. Finally, a brief discussion on future directions, challenges and opportunities in this field is also provided.