Enclosing the nitrogen cycle: Ammonia synthesis by NOx reduction

Nitrogen cycling (N₂-NO_x-NH₃) is essential for maintaining life as it is crucial in fertilizers and nucleic acids. However, the current NH₃ synthesis (N₂-to-NH₃) for fertilizers and energy requires large amounts of fossil fuels and greenhouse gas emissions, compromising its eco-economic significance. Meanwhile, approaches like selective catalytic reaction are applied to neutralize the toxic NO_x into N₂ but call for value-added NH₃ as the reduction agent. In this regard, directly converting harmful NO_x, one of the major environmental pollutants, into NH₃ is a promising way to balance the nitrogen cycle eco-friendly, which is still in its infancy. Recently, the electrocatalytic NO_x reduction reaction (NO_xRR) unveiled a potential route for the NO_x-to-NH₃ conversion. This review presents the latest progress in the electrocatalytic NO_xRR in reaction mechanism and catalysts design. It will provide a comprehensive understanding to guide future research in NO_xRR, aiming to offer sustainable chemistry and energy feedstocks for the carbon-zero economy.