Preparation And Photoelectric Performance Of Tin Oxide Modified Materials Based On Density Functional Theory

Overexploitation of traditional energy and increasing of environmental pollution become two major problems in the world today.Solar energy utilization and carbon dioxide conversion are hot research topics to solve the energy and environment problems.Owing to its advantages of good conductivity,fast electron transfer rate and low price,SnO₂ is the key material for photoelectric catalysis in solar energy utilization and carbon dioxide conversion.However,the wide band gap?3.6 eV?of SnO₂ has limited its application in some degree.At present,the common methods of modifying band gap of semiconductor oxide are element doping and semiconductor compositing.Based on this,author thinks that these methods can be used to adjust the band gap of SnO₂ materials,which can improve the photoelectric performance and broaden application in solar energy utilization and CO₂ conversion.In this paper,the density functional theory calculation method based on the first principle was used to systematically study the mechanism of SnO₂materials in the process of dye-sensitized solar cells and CO₂ conversion.Meanwhile,a series of M-S?M=Mg,Ca,Al,Ga?co-doped SnO₂ materials and MX₂/SnO₂?M=Mo,W;X=S,Se?nano-compositematerialswithgood photoelectric catalytic performance were designed and prepared.The theoretical calculation combining with experimental method was focused on exploring the electronic structure and photoelectric catalytic performance.The specific research contents are as follows:1.The adsorptions of fixed groups-COOH,-OH,-CN,-NH₂ and-SH of dye molecules on stoichiometric SnO₂?110?surface,Ov-SnO₂?110?surface and Pt-doped Sn O₂?110?surface were investigated respectively by density functional theory calculation.The calculations reveal that among three different SnO₂?110?surfaces,the adsorption energies of fixed group-CN,-NH₂,-SH,-OH and-COOH on Pt-doped SnO₂?110?surface are-2.041 eV,-2.639 eV,-2.966 eV,-2.204 eV and-2.204 eV respectively,which reach the maximum.Therefore,they are the most stable adsorption configurations.Among these five dye molecules,the bidentate chelate adsorption configuration of-COOH is most stable.At this point,the two O atoms of-COOH are bonded to the surface Pt and Sn₂,and dissociated H atom adsorbs on the surface O₆ site to form H-O₆bond.The dissociation has to overcome an activation energy of 0.93 eV,this process is exothermic by 0.57 eV.Therefore,dye molecule with-COOH group and Pt-doped SnO₂ photoanode are prior to selection in the preparation of dye-sensitized solar cells.2.The first principle calculation combining with solvation model was used to study the adsorption behavior and reaction mechanism of CO₂ on SnO₂?110?surface.The results show that the adsorption configuration of CO₂ slanting on SnO₂?110?surface?C2?with adsorption energy of-0.794 eV is the most stable configuration.Considering the solvation,all adsorption energies increase obviously,C2 configuration is still the most stable adsorption configuration.However,CO₂ bends with bond angle changing from 163.668°to 125.904°,which indicates that the solvation can affect the adsorption configuration of CO₂on SnO₂?110?surface.Meanwhile,it is found that as the number of water molecules increases,the adsorption energy for water molecules and CO₂co-adsorption increases,which is consistent with the solvation.In addition,in the process of CO₂ and OH to HCO₃^-,the enegy barrier reduces 0.15 eV.For CO₂ and H to HCO₂^-reaction,the reduced enegy barrier can reach 0.36 eV,suggesting that solvation can significantly reduce the energy barrier of CO₂reduction.The above results indicate that the solvation can increase the adsorption energy of CO₂ on SnO₂ surface and reduce the activation energy required for CO₂ reduction.3.Based on the theoretical calculation,the electronic structure and mechanism of the M-S?M=Mg,Ca,Al,Ga?co-doped SnO₂ materials were studied.The calculation results show that metal acceptors Mg,Ca,Al and Ga can assist S-O coupling by accepting two electrons from S atom,introducing new energy levels in Sn O₂ forbidden band,which make the band gap decrease to 0.770 eV,0.978 eV,0.920 eV and 0.979 eV,respectively.Thus,the photoelectric catalytic performance is enhanced.Based on this theoretical calculation,M-S?M=Mg,Ca,Al,Ga?co-doped SnO₂ with different doping ratios were synthesized by hydrothermal method,and the corresponding electrodes were prepared by dropping method.The photoelectric performance tests show that when the doping ratio is 5%,the photocurrents of M-S?M=Mg,Ca,Al,Ga?co-doped SnO₂ are 2.4?A/cm²,2.7?A/cm²,3.0?A/cm² and 2.8?A/cm²respectively,corresponding to the lowest electrochemical impedance.Overall,M-S?M=Mg,Ca,Al,Ga?co-doping can provide technical guidance and theoretical support for the design of SnO₂ materials with high photoelectric catalytic performance.4.The method of combining theoretical calculation with experiment was usedtoexplorethephotoelectriccatalyticperformanceof MX₂?M=Mo,W;X=S,Se?/SnO₂ nanocomposites.The electronic structures of the composites were studied by density functional theory calculation.Compared withSnO₂material?1.070eV?,thebandgapvaluesof MX₂/SnO₂?M=Mo,W;X=S,Se?nanocomposites are significantly reduced to0.141 eV,0.137 eV,0.133 eV and 0.008 eV,respectively.The population analysis suggests that the charges transfer obviously between upper MX₂?M=Mo,W;X=S,Se?and underlying SnO₂,which can improve the photoelectriccatalyticperformanceofSnO₂materials.The MX₂/SnO₂?M=Mo,W;X=S,Se?nanocompositesweresynthesizedby hydrothermal method.The electrodeposition method was used to prepare the corresponding electrodes with conductive glass?FTO?.The experimental results show that the photocurrents of MX₂/SnO₂?M=Mo,W;X=S,Se?nanocomposites are respectively 2.2?A/cm²,1.6?A/cm²,4.8?A/cm² and 3.0?A/cm²,and the electrochemical impedance are also smaller than that of Sn O₂ material.Therefore,MX₂/SnO₂?M=Mo,W;X=S,Se?nanocompositesaregood photoelectric catalytic materials.