A Theoretical Study Of Single/Double Atom Catalyst In Nitrogen Reduction Reaction

Ammonia（NH₃）is widely used and is an indispensable material in industrial production.At present,Haber-Bosch method is used to synthesize ammonia in industry,which consumes a lot of energy and generates a large amount of greenhouse gases.The electrochemical nitrogen reduction reaction（NRR）proceeds in mild conditions,so that can be one of the effective methods to improve the traditional industrial ammonia synthesis.High-efficiency electrocatalysts with low cost and excellent performance can improve the efficiency and yield of NRR.So electrocatalyst is one of the key objects for electrochemical synthesis of ammonia.First-principles calculations based on quantum mechanics and quantum chemistry can simulate and analyze the performance of electrocatalysts and provide a theoretical basis for experiments.This paper aims to analyze the catalytic performance of single and double catalysts（SAC,DAC）in NRR via first-principles calculations,and compare the two kinds of catalysts.The SAC and DAC are two-dimensional structures（TM₁N₃-graphene,TM₂N₆-graphene）in which metal atoms are embedded in N-doped graphene.The central metal atoms choose five different transition metals（TM=Mo,Fe,Co,Ni,Cu）,and the substrate is graphene doped with N atoms（N₃-graphene,N₆-graphene）.The reaction mechanism of NRR is affected by the number of catalyst active centers,so different reaction paths on SAC and DAC are discussed in detail.By comparing the reaction rates,we have obtained the best paths of NRR on SAC and DAC respectively,and it is proved that both of SAC and DAC exhibit excellent electrocatalytic performance in NRR.In particular,when N₂ is adsorbed by lying-on mode,the subsequent NRR processes by the Enzymatic mechanism,the catalytic efficiency of SAC is higher than that of DAC.In addition,by comparing five kinds of TM atomic active centers,it is found that the catalytic performance of single and double Fe atom complexes is better than the other four,especially the single Fe atom catalyst（Fe₁N₃-graphene）which only produed a little energy barrier（0.04 e V）at the rate determining step（RDS）in NRR.So Fe₁N₃-graphene can an efficient electrocatalyst for NRR.This work not only discusses and compares the high catalytic performance of SAC and DAC from the electronic level,but also proposes a new SAC catalytic idea,which proves that SAC performance is not worse than DAC in NRR electrocatalysis.