Electrocatalytic Nitrate Reduction to Ammonia Synthesis: Reaction Mechanisms, Catalytic Materials, and Future Perspectives

The large-scale production and utilization of nitrogen-containing compounds have greatly promoted the development of modern agriculture and the chemical industry, but have also resulted in increasingly severe nitrate contamination and an imbalance of the nitrogen cycle. The efficient conversion of nitrate into value-added ammonia not only contributes to pollutant remediation but also provides a promising route for green ammonia synthesis. Owing to its mild reaction conditions, potentially lower environmental impact, and compatibility with renewable electricity, electrocatalytic nitrate reduction to ammonia has attracted considerable attention in recent years. This process involves a multielectron transfer process involving numerous intermediate transformations, and its catalytic performance largely depends on the adsorption and conversion of key intermediates on the catalyst surface, as well as the suppression of the competing hydrogen evolution reaction. This review systematically summarizes recent advances in electrocatalytic nitrate reduction to ammonia, with emphasis on the reaction mechanisms and major reaction pathways, as well as the design strategies, structure-activity relationships, and performance enhancement mechanisms of metal-based, carbon-based, and composite catalysts. In addition, the main challenges in this field, including product selectivity, mass transport, in-situ mechanistic characterization, and long-term stability, are discussed. Finally, the construction of highly efficient catalytic systems and key directions for future research are outlined, with particular emphasis on nitrate valorization and sustainable ammonia synthesis.