| At present,with the increasing shortage of fossil energy,the effective conversion and storage of renewable energy are very important to the sustainable development of human society.The development of conversion and energy storage systems such as photocatalytic water decomposition,photocatalytic CO2 reduction and high-capacity lithium-air batteries have played an important role in solving the problems of energy shortage,environmental pollution and energy storage,providing scientific and technological support for achieving the"Double Carbon Target".However,low solar energy utilization,high photoexcited carrier recombination rate and slow electrode kinetic rate are the bottleneck factors that restrict the photocatalytic and electrocatalytic reaction.Therefore,looking for functional material with high activity and low cost is an effective way to improve the efficiency of photocatalysis and electrocatalysis.In this paper,we have focused on the key issues of structural stability and photocatalytic/electrocatalytic activity in heterogeneous hybrid materials via micro/nano structural design,doping,defects introduction and heterojunction regulation.Taking Bi-based,graphene and transition metal compounds materials as the main research objects,our investigations mainly included two sections:photocatalytic properties of heterogeneous hybrid materials and the electrochemical performance regulation of lithium-air battery.The main work is as follows:（1）The interface microstructure and photocatalytic properties of two-dimensional Zn Se/Bi OX（X=Cl,Br,I）vertical heterostructures are deeply studied by first principle calculation.It is found that the small lattice mismatch between Zn Se and Bi OX makes them have minimal interface relaxation and high interface binding energy when forming heterojunction.Moreover,Zn Se/Bi OX can form a stable type II semiconductor heterojunction with a direct band gap ranging from 1.78 e V to 2.06 e V.Their band gaps are significantly reduced compared with the single-layer materials,and the light absorption spectrums are strengthened in the ultraviolet-visible region.At the same time,Zn Se/Bi OX can form a strong built-in electric field to realize the effective separation of photogenerated electrons and holes in two different layers upon visible-light irradiation.The bandedge positions of the Zn Se/Bi OX heterostructures have demonstrated that the band levels of the VBM and CBM stride the oxidation and reduction potential for water splitting,which is suitable for the catalyst of photocatalytic decomposition of water.In addition,interlaminar biaxial strain can effectively regulate the band gap and band edge position of Zn Se/Bi OX,indicating the great potential of strain engineering in modulating the photocatalytic properties of van der Waals heterostructures.This work is helpful to better understand the internal mechanism of Zn Se/Bi OX interface structure enhancing photocatalytic performance,and is of great significance for the further development of low-cost and high-efficiency photocatalyst materials.（2）The photocatalytic CO2 conversion of 2D Sn S2 nanosheets modified by S-defect（Sn S2-VS）and carbon interstitial doping(Sn S2-Cint)is investigated by first-principles calculations.From a thermodynamic point,Sn S2-VS and Sn S2-Cint show narrower band gaps,suitable band edge position,red-shifted absorption spectrum and stronger light absorption,suggesting a better photocatalytic activity.Importantly,Cint can not only improve the electrical conductivity of Sn S2 nanosheet,but also prolong the lifetime of photoexcited carriers.Furthermore,we also explain the high activity and selectivity from the reaction kinetic view by calculating the Gibbs free energy of different intermediates in the process of CO2 reduction.It is demonstrated that the Sn S2-Cint can not only reduce the limiting potential（UL）of the whole reduction process to 2.77 V,but also have an excellent selectivity for CH3CHO and CH4 products through multi-electron reduction.For Sn S2-VS,the CO2 can be efficiently captured and reduced into CH3CHO and CH4 with a lower Gibbs free energy barrier of 3.08 e V,which is much smaller than the 3.70 e V of Sn S2.Our work provides a useful theoretical insight for VS and Cint on determining CO2 reduction property at Sn S2 nanosheets,which will help to design Sn S2 related materials for photocatalyst.（3）The ORR/OER catalytic performance of B-,N-doped and B-N-co-doped Stone-Wales（SW）defect graphene is studied by first-principles calculation.The results show that the synergistic effect of B-N codoping and SW defects activates the inertπelectrons of intrinsic graphene,resulting in the redistribution of electrons on its surface and the production of more active sites.At the same time,the synergistic effect optimizes the adsorption and desorption intensity of Li atom and O2 on the catalyst surface,promoting the adsorption and desorption reaction on the catalyst surface,which reduces the ORR/OER reaction overpotential(ηOR R=0.23 V/ηOER=0.29 V)and improves the catalytic reaction efficiency of the air electrode.In addition,combined with the principle of chemical reaction kinetics,the real reaction path of ORR/OER on the surface of the catalyst is simulated according to the adsorption energy of intermediate products.At the same time,the changes of free energy of each elementary reaction are studied and the rate-determining reaction steps are obtained.The results show that the overpotential of the catalytic reaction strongly depends on the adsorption behavior of the intermediates in the rate-determining step.In addition,taking BN-SWG as a test case,we find that BN-SWG does not promote the formation of side product Li2CO3.On the other hand,it will not lead to the decomposition of the dimethyl sulfoxide electrolytes,indicating that BN-SWG can improve the reversible cycle life without producing Li2CO3-like species in Li-O2 batteries.This work contributes to a better understanding of the ORR/OER process of non-metallic cathode catalysts for non-aqueous Li-O2 batteries,and provides a feasible way for the design of highly active cathode catalysts.（4）Based on the first-principles calculations,the cathode structure model of Mo6X6（X=S,Se,Te）nanowire is established to explore the ORR/OER catalytic activity of Li-O2battery.The results show that the high specific surface area of nanowires provides a large deposition site for the discharge products,which gives the Li-O2 battery better ORR/OER performance.On the other hand,the quantum confinement effect induces Mo6S6 and Mo6Se6 nanowires to exhibit metal properties,resulting in high electronic conductivity.At the same time,Mo6S6 and Mo6Se6 nanowires accelerate the adsorption and activation of intermediates in the catalytic process,reducing the ORR/OER reaction overpotential,(Mo6S6:ηOR R=0.47 V/ηOE R=0.24 V,Mo6Se6:ηOR R=0.49 V/ηOER=0.31 V,Mo6Te6:ηOR R=0.75 V/ηOE R=1.21 V)which improves the catalytic reaction efficiency of the air electrode.The NEB（nudged elastic band）calculations show that O2 is difficult to capture the non-metallic elements in Mo6X6（X=S,Se,Te）nanowires,which shows good structural stability and greatly improves the cycle performance of lithium-air batteries.This work contributes to an in-depth understanding of the ORR/OER process of transition metal cathode catalysts for non-aqueous Li-O2 batteries,and provides a useful reference for efficient screening and development of positive catalysts for lithium-air batteries. |
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