Construction Of Proton Transfer Channels And Intensification Of Membrane Performance Based On Metal-organic Compounds

Proton-exchange membrane fuel cells（PEMFCs）have received lots of research interest due to the high energy density,low working temperature and so forth.Proton-exchange membranes（PEMs）are the key components of PEMFCs,and the performance of fuel cells are always limited by the properties of membranes,including stability,ion conductivity and etc.Optimizing the structure of ionic channels is an effective method to improve the comprehensive properties of PEMs.Metal-organic compounds are characteristic of designable structures and abundant types,and attractive in constructing efficient ionic channels.In this study,various nanostructured metal-organic compounds（MOF,MOP and MOG）were prepared and used to investigate the the relationship between proton conductivity and the structure of ionic channel.The proton-conductive behavior of PEMs were improved by constructing continuous and regular ionic channels.The main research results are as follows:SPEEK hybrid membranes by incorporating HPW immobilized sulfonated metal-organic framework（MOF）:Phosphotungstic acid（HPW）was loaded into sulfonated UiO-66（S-UiO-66）via in-situ immobilization to prepare S-UiO-66@HPW,which was then incooperated into sulfonated poly（ether ether ketone）（SPEEK）to obtain hybrid membranes（SPEEK/S-UiO-66@HPW）.HPW and sulfonated ligands endowed UiO-66 with proton conductivity,and the window size of pores suppressed the loss of HPW.S-UiO-66@HPW provided hybrid membranes with regular ionic channels and optimized the distributions of ionic groups,which contributed to the enhancement of proton conduction of hybrid membranes.The proton conductivity of hybrid membranes（30 ℃,100%RH）reached 0.076 S cm^-1,which was 1.6 times that of SPEEK membrane.Molecular-level hybridization of SPEEK membranes by incorporating sulfonated metal-organic polyhedra（MOP）:Sulfonated MOP（SMOP）was prepared by post-functionalization of MOP-NH₂ with 1,3-propanesultone and then integrated into the SPEEK matrix to obtain hybrid membranes（SPEEK/SMOP）.SMOP could dissolve in the casting solution of SPEEK,which contributed to the molecular-level hybridization.SMOP provided additional ionic groups as well as affected the assembly of hydrophilic/hydrophobic segments of polymer,which optimized the structure of ionic clusters.The proton conductivity of hybrid membranes（30 ℃,100%RH）reached 0.091 S cm^-1,which was 2.1 times that of SPEEK membrane.Metal-organic nanogels（MOG）with sulfonated 3D continuous channels as proton conductor:Cr³⁺and sulfonated terephthalic acid（sBDC）were used as metal ions and ligands respectively.Metal-organic gels（Cr/sBDC-Gels）with 3D well-percolated structure was prepared via one-step sol-gel method.Sulfonated ligands endowed Cr/sBDC-Gels with intrinsic proton conductivity.The 3D interconnected framework contributed to the long-range continuous proton condution and suppressed the grain boundaries.Cr/sBDC-Gels possessed high proton conductivity(5.0-7.8×10^-3S cm^-1)and were regarded as superprotonic conductor even under low ion concentration(0.1-0.2 mmol m L^-1).The proton-transport efficiency of Cr/sBDC-Gels was～100higher than that of MIL-101-SO₃H pellet.