(Invited) Carbon-Based Single Ni Site Catalysts for Nitrogen Reduction Toward Electrochemical Ammonia Synthesis

Ammonia electrosynthesis using nitrogen and water has been attracting significant attention and can be easily used for distributed fertilizer production or fuel generation. However, electrochemically nitrogen reduction reaction (NRR) under ambient conditions is very challenging and largely dependent on active and selective catalysts. Herein, we report a new class of atomically dispersed Ni site catalyst, which exhibited the highest ammonia yield of 112 µg cm-2h-1 and a FE of 20 % in neutral electrolyte. The coordination of Ni sites with nitrogen was further verified by advanced X-ray absorption spectroscopy and electron microscopy, suggesting a coordination number close to 3. Density functional theory calculations provide insightful understanding on the possible structure of active sites and the relevant reaction pathway of the NRR on the single Ni site catalysts. Although we are not able to do the very expensive 15N2 isotope tests, extensive controls strongly suggest the atomically dispersed Ni-Nx-C coordination provides more intrinsically active sites than those in N-doped carbon for ammonia production throng the NRR, instead of possible environmental contamination. This work further supports that single metal sites catalyst with appropriate nitrogen coordination is very promising for the NRR and indeed improve the scaling relationship of transition metals.