Study Of "Transition Metal-nitrogen" Doped Pentagonal Graphene In Energy Conversion Reactions

The continuous consumption of fossil energy has led to the continuous intensification of the greenhouse effect and the continuous expansion of the energy gap.The demand for the development of efficient energy conversion catalysts is increasing.Among various new types of catalysts,carbon-based single-atom catalysts(SAC)have attracted wide attention from scientists due to their high utilization of metal atoms and high catalytic activity.Pentagonal graphene(PG)is a two-dimensional carbon-based material with unique porous structure,excellent electrical conductivity and good thermal stability.It can keep its electronic structure and catalytic performance unchanged at a temperature of 1000 K.This makes PG-based materials have broad application prospects in the fields of catalysis and nanoelectronics.The research object of this paper is pentagonal graphene doped with "transition metal-nitrogen" structure.And for the first time,transition metal(TM)and nitrogen atoms co-doped in pentagonal graphene.Among 40 different doping structures,we screened eight monolayers with structural characteristics of single-atom catalysts(TM-Nx-PG,TM is Sc,Ti,V,Cr,Mn,Fe,Co,and Ni,X=1).Density functional theory is used to calculate the structural configuration,surface gas adsorption energy,Gibbs free energy barrier,and overpotential of the intermediate product of the monolayer "TM-N1-PG" in the oxygen reduction reaction(ORR)and carbon dioxide reduction reaction(CO2RR).Binding electron structure analysis revealed the intrinsic connection between catalyst structure and catalytic reaction performance.The main research contents are as follows:(1)In Chapter 3,we explored the catalytic performance of monolayer TM-N1-PG for ORR reaction.The results show that the overpotential of the single-layer Co-N1-PG is 0.882 V,and the overpotentials of the other seven single-layer catalysts are all greater than 1.200 V.Theoretical results show that,among the eight catalysts,Co-N1-PG is a promising ORR catalyst compared with the other seven catalysts.(2)In Chapter 4,we explored the catalytic performance of monolayer TM-N1-PG on CO2RR.The results show that in the first step of the CO2RR protonation reaction,all eight single-layer catalysts will preferentially reduce CO2,which can well inhibit the hydrogen evolution reaction and exhibit excellent CO2RR selectivity.The main products of the eight monolayer catalysts in the CO2 reduction reaction are different.Sc-Ni-PG tends to reduce CO2 to CO via two-electron reduction path,and the reaction overpotential is 0.538 V.Cr-N1-PG,Mn-N1-PG,Fe-N1-PG,Co-N1-PG,and Ni-N1-PG tend to reduce CO2 to HCOOH through the two-electron reduction path.The overpotentials of the five catalyst reduction reactions are all less than 0.700 V.The overpotentials of Co-N1-PG and Ni-N1-PG monolayer reaction are 0.366 V and 0.335 V,respectively.Ti-N1-PG and V-N1-PG tend to reduce CO2 to CH4 through an eight-electron reduction path.The overpotentials are 2.207 V and 1.361 V,respectively.Theoretically,it shows that among the eight catalysts,Co-N1-PG and Ni-N1-PG are highly potential electrocatalytic CO2RR catalysts.The research results in this paper will provide a theoretical basis for the development of single-atom catalysts based on pentagonal graphene.