NiN4/Cr Embedded Graphene for Electrochemical Nitrogen Fixation

Owing to the heavy energy consumption and the massive CO2 emission during ammonia synthesis via Haber-Bosch process, a clean technology of nitrogen reduction electrocatalysis under ambient conditions is of significance for the sustainable energy conversion progress in future. In the study, the nitrogen reduction reaction of TM1N4/TM2 embedded graphene is comprehensively investigated using density functional theory calculations. Fully considering the activity and stability, our results reveal that NiN4/Cr anchored graphene exhibits the best catalytic activity via the enzymatic reaction pathway wherein the potential determining step is located at the first hydrogenation with an onset potential of 0.57 V, being superior to the commercial Ru-based material. Furthermore, compared with the isolated Cr atom decorated nitrogen functionalized graphene, the introduction of NiN4 moiety decreases Delta G(max) and enhances the electrocatalytic performance. According to the Mulliken charge analysis, the physical origin of the catalytic activity is ascribed to the electron transition between the supports and reaction intermediates. Overall, these results pave a way for the design of the high efficient electrode material for ammonia synthesis and provide a fundamental insight into the electrocatalysis.