Study On Electronic Structures And Electrocatalytic Properties Of Two-dimensional Materials

With the development of synthesis technology,more and more two-dimensional materials have been widely studied.Graphene,as a representative two-dimensional material,opens a new era in the research field of low-dimensional materials.Since graphene was successfully exfoliated in 2004,its unique planar structure and unique electronic properties have aroused people’s research interest.In addition to graphene,other two-dimensional materials,such as:silicene,germanene,borophene,phosphorene,transition-metal dichalcogenides have mushroomed,which greatly expands the performance and application of two-dimensional materials.Based on the excellent physical and chemical properties,two-dimensional materials show great potential application value and development prospect in various fields.From the perspective of energy storage,production and utilization,it can be used as a high-performance energy storage device or intrinsic catalyst in the field of electrochemistry.Different from threedimensional materials,two-dimensional materials have been widely studied for their advantages of large specific surface area,good mechanical properties and excellent electrical and thermal conductivity,becoming a hot research topic in the field of renewable energy.In this thesis,we systematically study the electronic structure and electrochemical properties of new two-dimensional materials,and explore their potential application in energy storage and conversion.In terms of energy storage,two-dimensional materials as excellent anchoring materials play an important role in lithium-sulfur batteries.From the perspective of energy production and utilization,the single atomic catalysts that form unique active centers by the coordination of two-dimensional substrate materials and metal atoms have rapidly developed into a research focus in this field.The change of Gibbs free energy can be improved by adjusting the local electron distribution in the active center,so as to improve the catalytic performance of the catalyst.The main research contents and conclusions are as follows:(1)Lithium-sulfur(Li-S)batteries as the most promising next-generation rechargeable battery have been a focus in the field of electrochemistry.One of the dominant obstacles inhibiting the development and application of Li-S batteries is the "shuttle effect" and thus developing new host materials to efficiently suppress the lithium polysulfides(LiPSs)shuttling has become urgent.In the present work,by combining the advantages of borophene and phosphorene,we propose borophosphene as a new potential anchoring material for Li-S batteries.It was found that borophosphene is semimetallic with a Dirac cone,endowing it with excellent electrical conductance to accelerate electron transport.It is of interest that the planar structure of borophosphene guarantees the strong LiPSs binding and easy diffusion.It is significant that the suitable adsorption energies(0.637～2.546 eV)of borophosphene can not only effectively inhibit the shuttle effect of soluble LiPSs but also reduce the migration barrier to realize the rapid charging and discharging process for Li-S batteries.It is therefore conclusive that borophosphene could be used as the potential anchoring material for Li-S batteries.(2)Single-atom catalysts(SACs)with ultrahigh atomic utilization ratio,high efficiency catalytic activity and low cost have been garnering attention in the field of electrochemistry.However,the bifunctional SACs for the water splitting are still encountering the common challenge of high overpotentials.In this work,a series of TM supported on two-dimension H4,4,4-graphyne monolayer(TM@H4,4,4-GY)were systematically studied by the firstprinciples calculations.The result show that Co@H4,4,4-GY and Pt@H4,4,4-GY are found to be the most efficient catalysts with low overpotentials of 0.04/0.45 and 0.17/0.69 V for HER/OER,respectively.Encouragingly,Ni@H4,4,4-GY as well is predicted to be the promising bifunctional catalyst for OER and ORR with lower overpotentials of 0.34/0.29 V,even superior to commercial IrO2 and RuO2,which demonstrated that H4,4,4-GY can be applied as the high activity,low-cost and promising electrocatalyst for HER/OER/ORR,In addition,our result shows that d-band center as the controlled variable could be adjusted to optimize the OER catalytic activity.(3)In this work,transition metal(TM)atom decoration is demonstrated to be a useful strategy to stabilize the unstable borophene.Interestingly,a new class of metal-shrouded borophene monolayers(TMB2)of high stability is predicted.In comparison to defect/doping induced activity in materials,metal-shrouded borophene with large specific surface area and high active site density illustrates a better choice for durable and efficient catalysts for specific electrochemical reactions.In particular,ReB2 as catalyst for N2 reduction reaction(NRR)for ammonia(NH3)with a record-low limiting potential of UL=-0.05 V and high Faraday efficiency(FE)of 100%is screened out from thirteen TMB2 candidates.More importantly,the electronic structure analysis provided more insight into the intrinsic origin of N2 activation.The PDOS and ICOHP of*N2 indicate that ReB2 with more a less negative ICOHP(-3.02)and a more antibonding orbital(2π*)filling are favorable for the N2 adsorption and activity.It is obvious that our results not only identify an efficient NRR electrocatalyst in particular,paving a way for sustainable NH3 production;but also explain the chemical and physical origin of the activity,advancing the design principle for catalysts for various reactions in general.