The state-of-the-art in the electroreduction of NO_x for the production of ammonia in aqueous and nonaqueous media at ambient conditions: a review

The synthesis of ammonia through the Haber-Bosch process has indirectly led to significant CO2 emissions. Electrochemical synthesis of ammonia from NOx under ambient conditions is key for achieving resource conservation and nitrogen cycle equilibrium. Herein, the state-of-the-art of the NOx reduction reaction to ammonia (NOxRR-to-NH3) is totally reviewed, with aspects on aqueous and nonaqueous electrolytes. In this context, the functional mechanism is briefly outlinedin aqueous and nonaqueous media, respectively, and the electrocatalyst design as well as the electrolyte modification in both solvents is summarized in detail. N-2 reduction in ionic liquids is presented, which provides meaningful suggestions for the electrocatalytic NOxRR-to-NH3 process in such media. The principal challenges faced by this field were discussed in the review. The primary obstacles are the disfavourable chemical kinetics, which includes the inert dynamics of NOx and hydrogen evolution reaction during the reduction process. Secondly, developing cost-efficient and performance-superior electrocatalysts and electrolyte systems is urgent for addressing such issues. At last, the outlook for future investigation is proposed.