Theoretical Study Of Two-dimensional Materials Doped With Non-metallic Elements For Electrocatalytic Nitrogen Reduction Reaction

Ammonia(NH3),as one of the important chemicals,has been widely used in industry and agriculture.Synthetic ammonia technology is the key cornerstone of the sustainable development of human society.At present,largescale synthesis of NH3 in industry is carried out by Haber-Bosch technology under extreme temperature and pressure,which not only consumes vast of energy,but also makes lots of pollution.Electrocatalytic NRR can use electrochemical methods to synthesize ammonia under mild conditions,prospectively solving the problems of high energy consumption and large pollution in traditional ammonia production processes.NRR also faces many challenges:how to effectively adsorb and activate inert nitrogen molecules,how to reduce the influence of HER,how to improve Faraday efficiency,etc.To settle these matters,we need to explore high-performance electrocatalytic materials.In recent years,two-dimensional materials(2DMs)can improve the catalytic efficiency more easily by heteroatom doping,defect engineering and other methods because of their structural characteristics.Therefore,this paper adopts density functional theory(DFT)to systematically study the internal mechanisms of the influence of non-metallic dopants to different 2DMs on the catalytic activity’ of NRR;which provides·a design idea for the development of new efficient and stable catalysts.The main topics of the research are stated as follows:(1)Study on the electrocatalytic performance of boron-doped graphene,graphyne,g-C3N4,BP,BN,Ti3C2O2 and V3C2O2 for NRR.A series of 24 different doping structure models were constructed,and the specific reaction mechanisms for NRR were determined respectively.Theoretical calculation results show that E*NNH can be applied as a descriptor of electrocatalytic performance for different two-dimensional doped structures,and it shows a‘volcano’ relationship with‘AGmax’.When the adsorption energy of NNH is around.1.20 eV,the corresponding doped structures have the best catalytic activity.Compared with the competitive reaction HER,when boron is doped on the surface of black phosphorus in an adsorbed state,it not only can effectively inhibit HER,but also has a lower thermodynamic energy barrier(0.94 eV),showing excellent NRR catalytic activity.Partial density of state shows there is a large overlap between p orbitals of boron atom and the π*orbitals of N2 near Fermi level,which leads to charge transfer,and the N2 molecule is fully activated,which promotes the subsequent protonation process series.(2)Study on the electrocatalytic performance of boron and p-block nonmetallic elements(B/C/N/O/Si/P/S/F/Cl)dual-doped graphene nanoribbons for NRR.A series of doping structures were constructed,and we put forward an intrinsic descriptor:Φ=(EX/EB)*(1X1/IB1),which includes two essential characteristics of doping elements(electronegativity and first ionization energy),providing a design guideline for experimentally exploring excellent NRR catalysts.There is a‘volcano’ relationship between Φ and △Gmax,where the dual boron doped structure,B1B2-1,tops at the peak(AGmax=1.06 eV).B1B21 can effectively inhibit the competitive reaction HER.The electronic structure analysis shows that the boron atom at the edge of B1B2-1 is sp2 hybridized,and the overlapping orbitals(pz-π*,spx,y-π*and spx,y-σ)are generated with the N2 molecule.The bonding and anti-bonding calculated by crystal orbital Hamilton populations also correspond to these results,which explains the origin of excellent catalytic performance.Meanwhile,the calculation of formation energy and molecular dynamic simulations verify that B1B2-1 have good structural stability.