Critical review in electrocatalytic nitrate reduction to ammonia towards a sustainable nitrogen utilization

Nitrate in wastewater poses a serious threat to ecological safety and human health. Electrocatalytic nitrate reduction (eNO3-R) to ammonia is a promising way, which can simultaneously achieve pollutant removal and resource recovery. This review focuses on the recent progresses in eNO3-R to ammonia towards a sustainable nitrogen utilization. The mechanisms of eNO3-R to ammonia are summarized from the electrochemical principles, reaction pathways and theoretical predictive modeling. Major electrocatalysts like single metals, bimetals and transition metal compounds are categorically concluded and compared. The main operating parameters including the applied potential, current density, pH of electrolyte, and inorganic ions are overviewed. Moreover, the couplings of eNO3-R to ammonia and ammonia recovery are reviewed for the first time. Finally, the challenges and opportunities of eNO3-R to ammonia are outlooked. The review provides good references for the further development of eNO3-R to ammonia.