| In recent years,people pay more and more attention to the conversion of CO2(CO2ER)into available energy by electrochemical method.By electrochemical method,CO2 can be converted into CO,methanol,formic acid and other available chemicals,which not only provides clean energy,but also alleviates the greenhouse effect caused by excessive emissions of CO2.It is important for CO2ER to develop electrocatalysts with low cost,high selectivity,high activity and high stability.In the previous work of our group,we developed the composite PCN-222(Fe)/C,which is made of porphyrin based metal organic framework(MOFs)PCN-222(Fe)combined with conductive carbon black.The composite shows high selectivity(FEco=91%)and stability(10 h),but its stability is still far from the actual application demand.The development of high-performance composite catalysts and the in-depth exploration of the composite of PCN-222(Fe)and high conductivity carbon materials will be of great significance to improve the performance of electrocatalysts and promote their application.The purpose of this article is to have 3D PCN-222(Fe)with multi-stage pore structure is compounded with carbon nanotubes(CNTs)and graphene with different high conductivity materials to prepare composite electrocatalyst with high activity site,high conductivity and high stability to carry out CO2ER research;in addition,improving its mass transfer performance to make the active site easier to contact with CO2 is also our research goal.PCN-222(Fe)is carried out by using nanoscale polystyrene microspheres The Macro-PCN-222(Fe)/C composite catalyst is rich in micropores,mesopores and macropores by etching,which can increase the contact area between the catalyst and CO2 and improve its CO2ER performance.The main research contents are as follows:1.Study on the CO2ER performance of PCN-222(Fe)/CNTsWe use a simple solvothermal method to combine PCN-222(Fe)and one-dimensional conductive nanomaterials CNTs in different proportions to form PCN-222(Fe)/CNTs catalysts.Through a series of structural characterizations such as IR,UV-Vis,PXRD,SEM,TEM confirmed the formation of composite sheath structure.Comparing the results of constant potential electrolysis experiments at various ratios and different loadings at-0.6 V vs.RHE potential,it was found that the 1:30 ratio composite has the highest selectivity for CO(FEco reached 92.5%),thanks to CNTs the higher conductivity and one-dimensional nanostructure and the synergistic effect between PCN-222(Fe)and CNTs increase the contact probability and contact area between the active metal center and CO2,and the surface molecule utilization rate of active molecules reaches 4.0%,the TOF is as high as 426.5 h-1,which is much higher than the PCN222(Fe)/C material(2.2%,44.5 h-1)doped with activated carbon in the previous work,which effectively reduces the cost of the catalyst.2.Study on the CO2ER performance of NP-PCN-222(Fe)/GOWe have successfully synthesized nano-sized NP-PCN-222(Fe)/GO-1 composite catalyst,and explored to use GO as the carrier of PCN-222(Fe).By adjusting the precursor reactant concentration,temperature and time,we obtained nano-sized 3D porphyrin MOF—NP-PCN-222(Fe).Under the condition of in-situ synthesis,the lamellar GO was combined with NP-PCN-222(Fe)in the form of solid(s)and dispersion(1)at 1:1,1:2,1:4 to obtain NP-PCN-222(Fe)/GO composite catalyst,the structure and morphology of NP-PCN-222(Fe)/GO composite catalyst were analyzed by IR,UV,PXRD and other characterization methods.The results showed that NP-PCN-222(Fe)/GO-s electrocatalyst may be due to the pre-120℃ drying of GO,and the hydroxyl group on the surface of GO may be partially lost,resulting in poor composite effect with NP-PCN-222(Fe)and poor overall catalytic effect.The catalyst material compounded in the form of dispersion and 3D porphyrin MOF—NP-PCN-222(Fe)have better synergistic catalysis.The best FEco(96%)and the lowest FEH2(1.4%)can be obtained at the composite ratio of NP-PCN-222(Fe)/GO-1=1:2.3.Study on the CO2ER performance of Macro-PCN-222(Fe)/CWe successfully prepared a monodisperse PS emulsion with a particle size of about 200 nm using traditional emulsion polymerization,and used this as a template to adjust the ratio of VDMF:VPS to containing a multi-stage pore structure by solvothermal make some holes.When the ratio of Macro-PCN-222(Fe)=1:1 to carbon black is 1:2,the Faraday efficiency of CO is higher than that of FEco(86%).Due to the improvement of PS solvent ratio,the pore structure of Macro-PCN-222(Fe)surface does not have the best FEco when it is close to 1:3 ratio,but the total efficiency of the catalyst is greater than 1:1 ratio,which is mainly due to the larger pore volume,higher active site percentage(2.6%),smaller charge transfer resistance Rct. |
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