Study On Electrocatalytic Behavior Of Two-dimensional Materials Based On Surface Modification

Since the successful synthesis of single layer graphene,various two-dimensional materials have been widely used in the fields of physics,chemistry,and materials science.The constructed single and diatomic catalysts based on the unique electronic structure of various two-dimensional materials,which were used as catalyst substrates,have also become a hot spot in the field of electrocatalysis.In the past few years,density functional theory（DFT）calculations have played an important role in the design of electrocatalytic materials and mechanism of exploration.However,the design of electrocatalysts with high activity,selectivity and low cost still confronts huge challenges.In this thesis,we constructed the models of two-dimensional transition metal carbonitrides,single atom catalysts based on transition metal carbides and diatomic catalysts based on hexagonal boron nitride（BN）monolayers.Subsequently,hydrogen evolution reaction（HER）on transition metal carbonitrides,nitrogen electrocatalytic reduction reaction（NRR）on single atom catalysts based on transition metal carbides and carbon dioxide electrocatalytic reduction reaction（CO₂RR）on diatomic catalysts based on BN monolayers were investigated in detail by density functional theory calculations.（1）Study of the electrocatalytic hydrogen evolution reaction on two-dimensional transition metal carbonitrides（MXene）Design highly active hydrogen evolution electrocatalysts still was faced with a great challenge in the field of electrocatalytic reaction.In the part of work,transition metal carbonitrides（MXene）are investigated as electrocatalyst of hydrogen evolution by density functional theory（DFT）calculations.The optimized structure,adsorption free energy and charge analysis on bare and functional terminated surface and transition metals（TMs）-modified M₃CNO₂ are systematically investigated.The calculated results reveal that all bare transition metal carbonitrides exhibit strong adsortpion strength between hydrogen and MXenes.Following|ΔG_H|<0.2 criterion,we found that only two Ti₃CNO₂ and Nb₃CNO₂ MXenes have the potential to be HER active electrocatalysts.In order to improve HER activity,we employed O as well as OH mixed groups and transition metal atoms modification on the Ti₃CNO₂surface for regulating HER activity.Subsequently,promotion on HER activity by the two methods were observed.In short,this work delivery new prospects into the design of high-efficiency and low-cost metal carbonitrides as noble-metal-free elctrocatalysts toward water splitting.（2）Study of electrochemical nitrogen fixation mechanism on single atom supported MXene（M₂CO₂,M=Ti,Mo）In this work,a series of single metal atom supported on Ti₂CO₂ and Mo₂CO₂monolayers were fabricated as efficient electrocatalysts for electrocatalytic N₂-reduction-reaction（NRR）by density functional theory calculation.Firstly,we calculated the binding energy between single metal atoms and MXenes,and the binding energy for Cu,Pt and Pd atoms were very small,leading to the unstability of the these electrocatalyst.Subsequently,by the first protonation of free energy calculations on NRR,we excluded some single-atom catalysts,which the free energy change of formation*NNH exceeds 0.8 e V.Our calculations results revealed that only single Ru or Mo atom anchored Mo₂CO₂ or Ti₂CO₂ monolayer possesses high NRR activity,and the calculated limiting potentials of Ti₂CO₂were more negative than those of Mo₂CO₂ due to the high conductivity of Mo₂CO₂.Moreover,N₂ can be efficiently reduced into NH₃ on Ti@Mo₂CO₂ through different reaction mechanisms,and the limiting potential was-0.64 V.Furthermore,we evaluated activity and selectivity of NRR on Mo@Mo₂CO₂ catalyst by comparing Gibbs free energy of each dinitrogen and hydrogen as well as the first dinitrogen protonation and hydrogen adsorption.It was found that N₂reduction pathway proceeds via distal or hybrid mechanisms,and the calculated overpotential were 0.16 or 0.19 V,respectively,indicating Mo@Mo₂CO₂ as a robust electrocatalyst for ENRR.This work afforded guidance for artificial N₂ fixation based on rational design of highly active MXene-based nanostructures.（3）Study of electroreduction of CO₂ to CH₄on double atom-anchored Boron Nitride monolayerIn this work,we fabricated a series of catalysts of double transition metal atoms（Mn,Fe,Co,Ni and Cu）anchored on BN monolayer were studied for the electrocatalytic CO₂ reduction reaction（CO₂RR）by density functional theory calculations.According to the reaction mechanism of CO₂RR,we selected the key intermediates along the direction of CH₄ products,such as*COOH,*HCOO,*CO,*HCOOH,*CHO and*OH to calculate the change of free energy.Based on large-scale calculations,we identified three promosing electocatalysts,including Fe₂@BN,Ni₂@BN and Cu Mn@BN.Subsequently,the detailed CO₂RR mechanisms were invetigated by free energy calculations.The thermodynamic results indicated that double Fe atoms,double Ni atoms and Cu Mn heteronuclear catalyst delivery highly active CO₂RR toward CH₄ production.The calculated limiting potential were-0.47 V,-0.39 V and-0.61 V on Fe₂@BN,Ni₂@BN and Cu Mn@BN catalysts surface,respectively.Overall,this work delivered in-depth investigations for double-atom catalysts and opens up new designs for highly efficient and low-cost BN-based nanostructures for CO₂ RR applications.