Powering the Remediation of the Nitrogen Cycle: Progress and Perspectives of Electrochemical Nitrate Reduction

Nitrate pollution in surface and ground waters has become a potent threat to ecosystem and human health. Electrochemical nitrate reduction is a promising strategy to directly convert excessive nitrates in water into environmentally benign dinitrogen gas or value-added chemicals such as ammonia under mild conditions. Once coupled with renewable electricity, it represents an eco-friendly and energy-efficient route for the recirculation of nitrogen species into the nitrogen cycle and economy. Understanding fundamental mechanisms of nitrate reduction is therefore crucial to design and develop high-performing electrocatalysts. In this review, we first discuss recent discoveries of reaction mechanisms for electrochemical nitrate reduction, focusing on the various pathways to desirable products (nitrogen and ammonia). The direct electron transfer and atom hydrogen transfer pathways are discussed in detail. We then summarize and discuss recent advances in catalytic materials spanning the material space from precious metal, nonprecious metal, and nonmetal catalysts. The existing challenges of electrochemical nitrate reduction are also highlighted. Finally, we provide the perspectives of the opportunities and outlook for the future development in electrochemical nitrate reduction.