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.