Preparation And Performance Research Of MOFs Enhanced Polyvinyl Alcohol-based Fuel Cell Conductive Composite Membrane

Nowadays,environmental pollution caused by fossil energy and depletion of natural resources are the two major problems that the world will face.Conventional cars mainly rely on gasoline as the main fuel,and it is urgent to develop new energy vehicles.As a popular type of research,fuel cells have the advantages of high efficiency,low pollution,and sustainability,and can be expected to solve the energy problems faced.As the core component inside the fuel cell,the proton exchange membrane should have efficient proton conduction performance and mechanical properties.Among them,metal organic frameworks（MOFs）have potential development prospects in the field of proton exchange membranes because of their highly regular pore structure,high stability,and adjustable pore structure.It is important but still challenging to develop high-performance proton exchange membranes（PEMs）,which should meet the following requirements:continuous proton conduction channels,efficient proton transfer,and good stability.This paper focuses on the preparation of composite membranes by two novel MOFs（Zn-MOF and Cu-MOF）and analyzes a series of properties such as mechanical properties,proton conduction performance and stability performance of these composite membranes:（1）Composite membranes were constructed by phytic acid（PA）impregnation of Zn-MOF with polyvinyl alcohol（PVA）and denoted as PVA@PA@Zn-MOF-X（X=0,2,4,6.wt%）.The novel Zn-MOF with high thermal and acid-base stability was synthesized from zinc salts and double ligands and can be used to carry PA as a proton carrier.The microstructure,thermal stability,mechanical properties,dimensional stability,and proton conductivity of the composite membranes were evaluated.It was found that impregnation of the Zn-MOF blends with PA solution promoted the stability of the composite membranes.In addition,the value of ion exchange capacity in the PVA@PA@Zn-MOF-4 composite membrane was relatively low(0.58 mmol g^-1),while it showed the highest proton conductivity of 1.85×10^-2 S cm^-1 at 80 ^oC and 90%RH.A large hydrogen bonding network was formed in the composite membrane,which consisted of carbonyl oxygen sites inside Zn-MOF,phosphate groups of PA and hydroxyl group of PVA,which improves the efficiency of proton transport.This is a referenceable strategy for the design and construction of high-performance fuel cell PEMs.（2）Cu-MOF was synthesized by sulfonic acid functional group modified ligands and metallic copper salts,while the composite membranes CL-PVA@Cu-MOF-X（X=5,10,15,20.wt%）were prepared by mixing Cu-MOF with cross-linked polyvinyl alcohol（CL-PVA）.The membranes were analyzed for structural characterization and performance measurements.It was found that the PVA membrane has higher mechanical stability performance after chemical cross-linking by the measurement results.Measurements revealed that CL-PVA@Cu-MOF-15 membrane had the highest water absorption and swelling rate of 108.4%and 62.5%,respectively.Cu-MOF modified by sulfonic acid functional groups provided proton transfer sites that enhanced the proton conductivity of composite membranes,and the proton conductivity of CL-PVA@Cu-MOF-15 reached the highest at 80 ^oC and 90%RH of 2.2×10^-2 S cm^-1.