Understanding first electron transfer kinetic process of electrochemical nitrate reduction to ammonia on Fe₂O₃ nanorods array

Electroreduction reaction of nitrate (NO₃RR) to ammonia (NH₃) using reproducible energy is an effective alternative strategy to energy-intensive Haber-Bosch process and potentially energy storage. However, the reaction needs coupling of multiple electrons and protons, considering it a grand challenge to NH₃ yield and selectivity affected by slow electron transfer kinetic processes. Herein, we investigate the electrode kinetics process by Tafel plots on Fe₂O₃ nanorods array electrocatalysts, confirming that the process of the first electron transfer is involved in the rate-determining step (RDS) for NO₃RR. The reaction rate constant (k) of the first electron transfer (NO₃^– + e^-→*NO₃) indicates that Fe₂O₃ electrocatalyst treated at 450 ℃ has a faster electron transfer kinetic and thus exhibits a higher NH₃ yield. Furthermore, operando EIS and in situ Raman spectroscopic characterizations demonstrate that electron gaining and losing process of Fe promotes the transfer of the first electron to NO₃^–, thus substantially accelerating the kinetic process of the RDS. These results provide key insight into the metal oxide-based electrocatalysts kinetic processes on the performance of NO₃RR.