Ammonia Synthesis from Water and Nitrogen Under Ambient Condition Using Single Atom Nickel

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Abstract

Our dependence on ammonia is not limited to development of fertilizers and other chemicals. Ammonia is being considered an energy vector, capable of being used for energy storage as well as fuel, due to its high energy density, ease of storage and transportation. Growing need for ammonia has forced development of alternate strategies for synthesis worldwide to serve as back up of Haber Bosch. Electrochemical ammonia synthesis is one such alternative. Earlier, we found that, nitrogen vacancy in metal-organic framework-derived disordered carbon is active for nitrogen reduction in alkaline electrolytes. We tried to investigate Fe-N4 sites for nitrogen reduction. It was observed that the activity improved as the loading of Fe was reduced. Finally, highest ammonia production efficiency was obtained for Fe free catalyst. Recently, we have developed single atom nickel on nanoporous carbon. They are derived from bimetallic organic framework of Ni and Zn. Surprisingly, single atom Ni with Ni-N4 sites is active for NRR. Its activity has been compared in different pH environment. The highest activity is obtained for neutral electrolyte followed by alkaline system, whereas, in acidic system, activity is the least. Its activity is about 110 µg mgcat h-1 in alkaline medium and three times higher in neutral media. It has surpassed activity of previously reported catalyst The stability of the nitrogen-doped electrocatalyst was demonstrated during an 18-hour continuous test with constant production rates. This work provides a new insight into the importance of non- precious metal based single atom catalyst for NH3 synthesis at ambient conditions. We have also done isotopic study to confirm the source of ammonia.

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