| The continuous development of science and technology in human society not only brings great convenience to human society,but also leads to some problems.The problem of environmental pollution is particularly prominent.Because of the huge carbon emission from industrial production,which has caused global warming and other major problems,it is particularly important to control carbon emission and effectively recover carbon dioxide in the atmosphere to solve environmental problems and recreate high-value products.Recently,carbon dioxide can be reduced through electrochemical method,coupling the electricity generated by clean energy.This method is a potential solution and has attracted the attention from researchers.Unfortunately,carbon dioxide is a kind of thermodynamically stable molecule,and its reduction reaction is relatively slow in kinetics and mass transfer rate,so that a higher overpotential is needed to overcome for the reaction.In order to reduce carbon dioxide to high-value products by electrochemical method,it is necessary to design suitable catalysts to reduce the reaction energy barrier.The evaluation of a carbon dioxide electroreduction catalysts mainly focuses on the following points: the types of reduction products,Faraday efficiency,current density and stability.At present,except for copper,most of the electrocatalysts can only reduce carbon dioxide through two electron processes,that is,the products are only formic acid and carbon monoxide.Compared with hydrocarbon products,the value of these two products is relatively low.Therefore,it is very important to build suitable catalysts to reduce carbon dioxide to high-value hydrocarbons.However,metalmetalloporphyrin framework(MMPFs)is advantageous to the adsorption of carbon dioxide molecules in the reduction process because of its ultra-high specific surface area and abundant pore,and its porphyrin center and metal linker both have catalytic activity.Therefore,metalmetalloporphyrin framework can be used as a potential carbon dioxide reduction reaction electrocatalyst.In chapter three,we focused on the copper-based metalloporphyrin framework,using [5,10,15,20-tetra(4-carboxyphenyl)porphyrin]-Cu(II)(Cu-TCPP)and copper nitrate to construct MOFs(Cu-TCPP MOFs)based on copper porphyrin,which showed lamellar morphology and a large number of nanopores.Then,the relationship between the morphology,element state and the activity of electrocatalytic reduction of carbon dioxide was studied,and compared with the corresponding single molecule porphyrin catalyst.It was found that the construction of copper-based copperporphyrin MOFs greatly improved the performance of carbon dioxide electroreduction compared with single molecular porphyrin catalyst,which provided a good idea for the construction of new heterogeneous electrocatalysts for carbon dioxide reduction reaction.In chapter four,we continued to use the solvothermal method to construct the copper based metalloporphyrin frameworks(M-TCPP MOFs)with different metallic porphyrin and systematically studied their morphology and chemical group information.Additionally,we screened out the copper-based zinc porphyrin frameworks(Zn-TCPP)can be used as bimetallic catalysts.In view of the poor selectivity to hydrocarbons,carbon nanotubes(CNTs)were introduced to MOFs in order to improve its electron transport mechanism.Then the effect of the relative content of CNTs on catalytic performance was explored.Finally,the current density of the modified Zn-TCPP MOFs doped with CNT complex(Zn-TCPP MOFs@CNT)is 5.3 times higher than that of Zn-TCPP MOFs without carbon nanotubes at the optimal potential.The introduction of carbon nanotubes into the materials can improve the electronic transport of the materials and promote the co-catalysis of bimetallic in the catalysts,which provides a new idea to design and build efficient electrocatalysts for carbon dioxide reduction reaction. |
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