Theoretical Study Of Graphene-based Metal Catalyst’s Electrocatalytic Properties On Nitrogen Reduction Reaction

The process of ammonia synthesis from nitrogen plays an important role in ecological cycle and industrial production.Unlike the ammonia’s industrial production with highly pollution and large energy consumption,the electrochemical synthesis of ammonia is favored,due to its ability of environment friendly feature,energy saving and its mild reaction conditions.Although there are many potential advantages of electrocatalytic nitrogen reduction reaction,due to the low efficiency and poor reaction selectivity of the existing electrocatalyst,it can not be put into practical use,and the need to develop a new type of nitrogen reduction electrocatalyst is particularly urgent.Two-dimensional materials have become the most potentially valuable electrocatalyst due to their excellent electronic properties and the large number of active sites provided by the huge specific surface area.Graphene is the first two-dimensional material which was discovered,but its surface is chemically inert.In order to make full use of the excellent electrical conductivity of graphene,the method of doping hetero-atoms experimentally was used to change its surface and electronic properties,making it to be an effective electrocatalyst.Based on density functional theory calculations,this thesis designed and studied the electrocatalytic nitrogen reduction reaction（NRR）ability of some bimetallic atoms and nitrogen atoms co-doped graphene,as well as the small molybdenum clusters supported on the surface of graphene’s NRR catalyze performance,we have got this results:（1）Metal&molybdenum&nitrogen atoms co-doped graphene shows good electrocatalytic nitrogen reduction reaction（NRR）performance.The additional metal atoms will change the electronic properties of molybdenum atoms and promote catalytic reactions on the molybdenum’s surface.Among all the tested structures,（Cd,Mo）,N/Graphene has the best catalytic performance of NRR,and its onset potential is 0.308 V.Meanwhile,the catalytic property of mixed bimetallic supported on N-doped graphene is generally better than single molybdenum atom catalysts supported on N-doped graphene.Our calculation is confirmed that the key intermediates of the reaction may be transferred between two active metal atoms,which provides a new idea for reducing the barrier of nitrogen reduction reaction.（2）Small molybdenum clusters which supported on graphene substrate can catalyze the nitrogen reduction reaction.Among them,manufacturing defects on graphene can increase the stability of the cluster,it will reduce the catalytic ability of the reaction and increase the onset potential of the NRR.On the other hand,compared with the three molybdenum atom clusters,the catalytic performance of four molybdenum atoms clusters increased.The onset potential of Mo₄/Graphene is 0.456 V,which demonstrates good catalytic ability of NRR.In summary,the calculation results of the thesis indicate that bimetallic atom-doped graphene and small cluster supported on graphene both have good catalytic abilities of nitrogen reduction reaction,and may be applied in experiments for new electrocatalytic materials.