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Study On Enhancement Of Electrochemistry And Photoelectric Conversion Efficiency Of Binary Metal Sulfides Modified By Carbon Material And Their Heterogeneous Structures

Posted on:2020-10-14Degree:MasterType:Thesis
Country:ChinaCandidate:K ZhangFull Text:PDF
GTID:2381330575963005Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
Although the economy of society has shown a trend of sustained growth in recent years,the constant emergence of resource and environmental problems haunts the earth at the same time.Research and excavation of environment-friendly and renewable resources seems to be the solution to this problem.Solar energy stands out from its advantages of continuous renewable,eco-friendly and non-polluting,low cost and abundant earth reserves,and has got the attention of scientific field.Solar cells,as a shining star in the energy-related community,can make a directly shift from solar energy to electrical energy.Dye-sensitized solar cells(Dye-sensitized Solar Cells,DSSCs)as the third generation of solar cells with its simple production process,cheap cost,environment friendly and high photoelectric conversion efficiency characteristics,has become the focus of energy field over the past few decades.The working system of dye-sensitized solar cells consists of three main parts:a counter electrode(CE),a photoanode made of TiO2 sensitized by the dye,and an electrolyte containing I3-/I-as the redox couple,which is injected between the CE and the photoanode.In the traditional case,the electrode is often a metal Pt.It can not only guide free electrons and form cyclic circuits,but also collect electrons and catalyze the redox reaction of iodine ions in the electrolyte.On the one hand,the counter electrode with its excellent catalytic performance plays a decisive role in the DSSC operation system.On the other hand,the traditional CE of Pt still has some defects.One is that Pt is very precious as noble metal and it has very little reserves in the earth.Another one is that Pt is very complex to prepare,and it is readily decomposed to PtI4 in the electrolyte.Therefore,it is meaningful to look for some materials including the merits of excellent catalytic properties,cheap and abundant reserves to replace precious metal platinum.In previous research works,the synthesis and application of metal oxides and metal sulphides have been reported as the counter electrodes in the DSSC.Due to the weak conductivity and catalytic activity of a single material,the corresponding PCEs of DSSCs are undesirable.On the one hand,carbon materials are introduced to improve the conductivity.On the other hand,an attempt is to introduce heterogeneous structures between different metal sulphides to improve the catalytic activity of electrode materials.The major research materials in this paper including MoS2,MoS2@SnS2,CuS@ZnS,CuS@Cu7S4,and attempt to modify these materials by introducing carbon materials,including unshaped carbon,reduced graphene oxide,nitrogen-doped reduction graphene oxide.Then the paper has used traditional technology to make the counter electrodes of DSSCs and explored their optical and electrical properties.This thesis can be summarized six aspects:(?)Research situation of solar cells and dye-sensitized solar cells is briefly introduced and the working principle of DSSC is introduced.The research situation of nanomaterials of binary metal sulfides and carbon materials including graphene is briefly introduced.The experimental significance of this thesis is discussed.(?)The experimental supplies,experimental ideas,experimental equipment and characterization methods used in the experiment are briefly introduced.(?)Nanocomposites of floriform MoS2 and amorphous carbon were prepared and used in the electrode of dye-sensitized solar cells,the amorphous carbon was introduced by glucose solution.The experimental results revealed that the MoS2@C(0.5M of concentration of glucose solution)has the best performance of electrical and optical properties,including photoelectric conversion efficiency(PCE = 6.93%).Under the same conditions,the PCE of pure MoS2 CE is 5.24%,while the PCE of Pt CE is 6.68%,and it is obvious that the performance of MoS2,which is much weaker than Pt,has been greatly improved through the amorphous carbon modification.(?)Using a simple method to prepare flower-like and netty MoS2@SnS2 composites.The results display that the PCE values of the netty nMoS2@SnS2 and flower-like fMoS2@SnS2 CEs are 7.63%,7.08%,respectively.Under the same conditions,that of Pt,pure SnS2,pure nMoS2 and pure fMoS2 is 7.38%,6.67%,5.78%and 5.37%,respectively.This shows that we have achieved the performance enhancement by using heterogeneous structure,and nMoS2@SnS2 is expected to be a good substitute for Pt with excellent photoelectric properties and chemical stability in our experiment.(?)By using simple hydrothermal method to synthesize heterogeneous cauliflower CuS@ZnS,the morphologies of heterogeneous structural materials were controlled by adjusting the material ratio of reactants,and reduced graphene oxide(rGO)was introduced to optimize its properties.The results show that the rGO-CZS nanocomposite has the best morphology and the best photoelectric performance when Cu:Zn=3:2.Compared with the photoelectric conversion efficiency(7.61%)of Pt,the rGO-CZS has reached 8.45%and achieved a substantial improvement.At the same time,30 cycles of CV test curves do not have the apparent changes and shifts,this shows that rGO-CZS CE achieves excellent chemical stability in the solution.(?)The porous and spherical Cu7S4@CuS nano-heterogeneous material was synthesized by solvent thermal method,and it was found that the morphologies and structures of nanocomposites changed gradually with the difference of synthesis temperature.When the synthesis temperature is as high as 210?,the surface of the nanocomposites appears uniform and clear porous structure.UV-visabsorption spectra show that the Cu7S4@CuS of 210? has a stronger absorption about visible light than other samples.Althoughthe results of CV test show that it also has relatively good catalytic ability and chemical stability,Cu7S4@CuS is still inferior to Pt.Therefore,we introduce nitrogen-doped graphene(nGO)to optimize its conductivity,catalytic capacity and chemical stability.Finally,the Cu7S4/CuS@nGO CE has achieved 9.14%PCE and excellent photoelectric performance and chemical stability.
Keywords/Search Tags:Dye-sensitized solar cell, Counter electrode, Graphene, Molybdenum disulfide, Copper sulfide
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