Electrocatalytic Reduction Of CO₂ With Metal-organic Frameworks Based On Indium And Porphyrin Cobalt

Fossil fuel is the main source of energy at present.With the continuous growth of energy consumption,the content of CO₂ in the atmosphere increases year by year,and brings a series of environmental problems,such as greenhouse effect,glacier melting,sea level rising,desertification area increasing and so on.In order to alleviate the harm caused by elevated CO₂ concentration in the atmosphere,it is necessary to make effective use of CO₂ while controlling industrial emissions and afforestation.Using renewable intermittent electric energy to reduce CO₂ to high-quality chemicals is a feasible way to effectively utilize CO₂,and it is also the frontier direction of current electrocatalysis research.However,the molecular structure of CO₂ is stable,the thermodynamic energy barrier is large,and it is difficult to activate,so efficient electrocatalysts are urgently needed to reduce CO₂.In addition,there are many ways to produce different products in the process of CO₂ electroreduction,so the selectivity of the catalyst is also a key factor to improve the catalytic performance.Therefore,it is urgent to develop efficient and highly selective materials for CO₂ electrocatalysis.In this paper,we used Indium-based and cobalt porphyrin-containing metal-organic frameworks(MOFs)as catalysts for CO₂ electroreduction(CO₂RR)to achieve the efficient and highly selective reduction of CO₂.The specific research contents are as follows:1.Indium-based metal-organic framework for high-performance electroreduction of CO₂ to formate.Indium-based MOF(In-BDC)materials were synthesized by hydrothermal method with In cluster as metal center and 1,4-terephthalic acid(H₂BDC)as ligand.In-BDC was the first MOF material of indium-based to be used in the electroreduction of CO₂,and it could selectively reduce CO₂ to formate.Its Faraday efficiency(FE^-_HCOO)was as high as 88%,and it had high catalytic selectivity and conversion frequency(TOF=4798 h^-1).In addition,In-BDC exhibited great long-term stability and good durability in the electrocatalytic process.Indium-based MOF with a similar structure could also reduce CO₂ to formate efficiently,which proved that carboxylic acid In-MOFs were efficient catalysts for CO₂ electroreduction.2.Two-dimensional metal-organic framework nanosheets with Cobalt-porphyrins for high-performance CO₂ electroreduction.Water-stable two-dimensional Zr-BTB nanosheets were synthesized by using Zr₆cluster as metal center,1,3,5-(4-carboxyphenyl)-benzene(H₃BTB)as ligand and benzoic acid as regulator.Then the catalytic cobalt porphyrin[TCPP(Co)=(5,10,15,20)-tetra(4-carboxyphenyl)-porphyrin Co^II]was immobilized on the Zr-BTB nanosheets,then the TCPP(Co)/Zr-BTB material was successfully synthesized.TCPP(Co)could reduce CO₂ to CO by itself.When TCPP(Co)was fixed with Zr-BTB nanosheets,its Faraday efficiency(FE_CO)was increased to 77.2%and it had ultra-high turnover frequency(TOF=4768h^-1).In addition,TCPP(Co)/Zr-BTB was modified by adjusting the spacing effect to change the microenvironment around TCPP(Co).Three kinds of post-modified two-dimensional nanosheets(TCPP(Co)/Zr-BTB-PABA,TCPP(Co)/Zr-BTB-PSBA and TCPP(Co)/Zr-BTB-PSABA)were obtained,and the FE_CO was significantly increased to 85.1%.Therefore,post-modification is a reasonable and effective means to improve the catalytic activity of MOFs.At the same time,the long-term stability of MOF electrocatalyst could be improved by optimizing the buffer capacity of electrolyte solution.