Electrocatalytic upgrading of nitrogenous wastes into value-added chemicals: A review

In response to the ever-increasing global population and the growing demand for energy and food, human activities have exerted a substantial impact on the global nitrogen cycles. In this context, the electrocatalytic upgrading of nitrogenous wastes into high-value chemicals under ambient conditions, ideally powered by renewable electricity, emerges as a promising approach to concurrently manage nitrogen-containing wastes and facilitate sustainable production of valuable chemicals. This review presents the electrochemical "waste-to-valuables" concept by discussing its practicality in terms of waste removal efficiency, valuable production efficiency, downstream recovery of valuables, potential applications, and economic feasibility. Specifically, the electrocatalytic upgrading of nitrogenous wastes, i.e., nitric oxide and nitrate as representative air and aqueous pollutants, respectively, into high-value-added chemicals, i.e., ammonia via nitric oxide/nitrate reduction and urea/amide/amine via nitrogen-integrated carbon dioxide reduction is focused. Targeting nitrogenous waste exhausts/streams with low/high concentrations, reactor design and catalyst design principles are reviewed with representative examples. Finally, the major challenges and opportunities associated with the practical applications of the "waste-to-valuables" concept are discussed.