Modification Of MOFs And Their Enhanced Electrocatalytic Performance For Carbon Dioxide Reduction

Since the 20th century,the development and progress of science and technology have led to increasing demand for fossil fuels,resulting in carbon dioxide emissions.Excessive emissions of greenhouse gases inevitably cause a series of environmental problems.The reduction of carbon emissions and the conversion of carbon dioxide have been a major direction for people to alleviate environmental stress in recent years.Therefore,the development of efficient carbon dioxide reduction catalyst is the direction of researchers’efforts.Metal organic framework materials（MOFs）are potential catalysts for carbon dioxide reduction reaction with many advantages such as three-dimensional pore structure,large specific surface area,definite metal sites and crystal structure and strong adsorption capacity for carbon dioxide.But most MOFs lack good electronic transmission capability.Therefore,modification of MOFs to improve its electron transfer efficiency is an effective way to solve this problem.In this paper,MOFs were used as the carrier and modified by the following methods to improve the ability of its electrocatalytic carbon dioxide reduction reaction.1.Taking UiO-67 as the contrast,the UiO-67-Cu was synthesized by the one-pot method using copper foam as the copper source.Copper foam,a new material with a large number of holes,was used to modify MOFs so that they could have metal catalytic sites.Compared with UiO-67 without Cu doping,the catalytic performance of UiO-67-Cu has been greatly improved,which shows that the introduction of copper sites enables UiO-67-Cu to have the good electrocatalytic capability of carbon dioxide reduction reaction,selectively reducing carbon dioxide into formic acid with the Faraday efficiency（FE）of 70%.However,the Faraday efficiency of UiO-67 is only 1%2.Based on the doping of metals and the introduction of functional external molecules,this work introduced the conductive molecule,pyrrole（Py）,into the channels of MOF-545-Co and then induced pyrrole polymerization at low temperature to obtain MOF-545-Co（?）PPy.The MOF-545-Co（?）PPy revealed good conductivity and can reduce carbon dioxide into carbon monoxide at-0.8 V（vs.RHE）.From MOF-545-Co to MOF-545-Co（?）PPy,FE increased from 58%to 98%and TOF reached to 785 h^-1,confirming introducing conductive molecules to improve the conductivity and catalytic performance of MOF is effective.3.Similarly,based on MOF-545-Cu,the mixed solution of MOF and polyacrylonitrile was made into nanofibers by electrostatic spinning and the nanofibers were further transformed into metal-doped nitrogen-carbon materials by pyrolysis.It was verified that the morphology,size and structure of nanofibers were basically preserved in the carbon material（MCP-500）after 500℃.Compared with MOF-545-Cu,the performance of the electro-catalytic carbon dioxide reduction reaction was greatly improved.MCP-500 can reduce carbon dioxide into carbon monoxide at-0.8V（vs.RHE）,with FE up to 98%and MOF-545-Cu only 10%.