Unique two-electron transfer pathway of Bismuth nanocrystal for enhanced N2 electroreduction revealed by in situ infrared spectroscopy

Due to the alarming increase in anthropogenic greenhouse gas emissions, there is an urgent need to replace the fossil fuel-driven Haber-Bosch process with green ammonia production. Electrochemical nitrogen fixation has shown preliminary promise for industrially ammonia synthesis, but an in-depth mechanistic understanding of the nitrogen reduction process remains limited. Herein, a unique dinitrogen desorption mechanism for the nitrogen reduction reaction is detected on the bismuth nanocrystals, which may explain some intriguing phenomena reported in previous works, including (1) why hydrazine is still generated in some nitrogen reduction reactions that do not follow the alternating pathway, and (2) a minor change in bismuth particle size can lead to a dramatic change in NRR performance. In addition, the experimental and theoretical calculation results reveal that the dinitrogen desorption pathway involving the transfer of two electrons usually shows lower energy barriers and faster reaction kinetics, resulting in a dramatic enhancement in NRR performance.