Preparation And Properties Of Proton Exchange Membrane Based On Carbon Nanotubes/Metal-organic Frameworks Materials

Metal organic frameworks（MOFs）are crystalline porous materials constructed from metal ions or metal clusters and organic linkers.In recent years,MOFs materials have received much attention as proton conductors in the fuel cell field because of their high specific surface area,rich structural tunability and functional porous surfaces that can accommodate a wide range of guest molecules as proton carriers and systematically modulate proton concentration and mobility in the available space.Scientists have focused MOFs on the development of high-performance polymer membranes as proton exchange membranes（PEMs）for fuel cell applications.As the core component of the proton exchange membrane fuel cell,the life of the proton exchange membrane directly affects the performance,cost and life of the battery.At present,the commercial proton exchange membrane is mainly the Nafion series membrane of Du Pont in the United States,although this kind of membrane has high proton conductivity,good chemical stability and mechanical properties,but due to high cost,low proton conductivity under high temperature conditions,poor gas barrier performance and other shortcomings limit its further commercial application.Based on this,a series of carbon nanotube/metal-organic framework composite proton exchange membranes were prepared by using organometallic frameworks as building blocks and organic-inorganic composite compounds by using organometallic frameworks as building blocks,and organic-inorganic composite modifications.The main contents of this paper are as follows:（1）The CNTs were acidified and oxidized,silica（SiO₂）was selected to surface coat the CNTs,on the basis of which ZIF-8 nanoparticles were grown in situ,and then ZIF-8-SiO₂@CNTs（ZSC）was compounded with SPEEK to prepare SPEEK/ZIF-8-SiO₂@CNTs（SPEEK-ZSC）composite proton exchange membrane.The coating treatment of CNTs by SiO₂avoids direct contact between CNTs and enhances the dispersion of CNTs in the matrix.ZIF-8 grows uniformly on the surface of the SiO₂@CNTs,which improves the dispersion and interfacial compatibility of ZSC in SPEEK,and contributes to the improvement of the mechanical properties of ZIF-8.At 80 ℃,the proton conductivity of SPEEK/ZSC-0.5 composite membrane reached 38.1 m S/cm.In 2 M methanol fuel,the highest power density of SPEEK/ZSC-0.5 composite membrane was 38.9 m W/cm²,which was higher than that of pure SPEEK membrane of 30.3m W/cm².In addition,the battery stability test results also show that the SPEEK/ZSC-0.5 composite film still has good stability over the pure SPEEK film after continuous operation at 80℃ for 100 h.（2）CNTs were acidified and oxidized,and in the presence of CNTs,acidic groups-SO₃H and basic groups-NH₂were introduced into UiO-66 at the same time to prepare acid-base coexisting MOFs material UiO-66-（NH₂）（SO₃H）（UNS）grown on CNTs,and then the hybrid nanomaterials UiO-66-（NH₂）（SO₃H）-CNTs（UNSC）were incorporated into the SPEEK matrix to prepare SPEEK/UiO-66-（NH₂）（SO₃H）-CNTs（SPEEK/UNSC）composite proton exchange membranes.CNTs provide a good growth platform for UNS,improve the dispersion of UNSC in the matrix,and the large aspect ratio of CNTs is also conducive to the formation of a continuous proton transport channel in the SPEEK matrix.The different push-pull forces of acid-base groups on protons in UNSC effectively increase the transport rate of protons in the material.At 80 ℃,the proton conductivity of SPEEK/UNSC-1composite film reached 39.4 m S/cm,which was 1.5 times that of pure SPEEK film under the same conditions;the maximum power density of SPEEK/UNSC-1 composite film in 2 M methanol solution reached 55.7 m W/cm²,and the open circuit voltage of the film was always maintained above 0.6 V in the 100 h battery stability test,showing good stability.