Regulating the hydrogen transfer pathways for electrochemical nitrate-to-ammonia at industrial current density

Electrochemical nitrate reduction offers a sustainable route for ammonia synthesis, of which the practical application is still limited by competing hydrogen evolution at industrial current density. The fundamental obstacle lies in the presence of excess *H not fully consumed by the nitrogen-containing intermediates during the hydrogenation processes. Here, the hydrogenation pathway on Cu₂O was regulated by cerium doping for promoting the nitrate-to-ammonia conversion. On pristine Cu₂O with the Cu⁰/Cu⁺ sites, the NO₃^--to-*NO and subsequent *NO-to-NH₃ processes follow the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) hydrogenation routes, respectively. Apart from the above sites, Ce-Cu₂O possesses additional Cu-O-Ce sites to enable the L-H pathway for the overall NO₃RR process. Balancing the intermediates hydrogenation pathways could avoid the fierce H₂ evolution derived from the residual *H, which guaranteed the high ammonia Faradaic efficiency (96.48%) for Ce-Cu₂O. This work offers mechanistic guidance for regulating the hydrogen transfer routes in other multistep electrocatalytic hydrogenation reactions.