Fabrication Of High Temperature Proton Exchange Membrane Based On Layer-By-Layer Self-assembly Technique

Layer-by-layer(LBL)self-assembly technique could efficiently construct the layered membranes nanoscopically and it has attracted more attention in the field of bionics,clean energy and microelectronics.The aim of this research to develop the multilayered membranes with the ordered deposition of components using LBL self-assembly technique.The ultrathin membranes composed of polyurethane(PU)as polycations,chitosan(CS)and the inorganics based on carbon nanotubes(CNT)as polyanions have been synthesized with layer by layer(LBL)self-assembly technique.The inorganics including carbon nanotube oxide-cadmium telluride(OCNT-CdTe)and carbon nanotube-cadmium telluride(CNT-CdTe)were prepared with the assembly of OCNT or CNT with CdTe nanocrystals.Most importantly,phosphoric acid(PA)molecules could be combined and formed PA molecule chains spontaneously while the LBL self-assembly membranes were immersed into PA solution.As the result,the proton conductivity of membranes were improved obviously.Specifically,(PU/CNT-CdTe/PU/CS)150/60%PA membranes exhibited the maximum proton conductivity of 6.82×10-2 S/cm at 150℃.Subsequently,successful preparation of anhydrous proton exchange membranes(PEM)based on graphene oxide(GO)as polyanions,polyurethane(PU)and poly(diallyldimethylammonium chloride)(PDDA)as polycations have been demonstrated by identification of the ordered distribution of components and compact structure.While the prepared membranes were immersed into phosphoric acid(PA)solution,phosphoric acid molecules were combined with the formation of phosphoric acid doped membranes.Although PA played a dominant role in proton conduction,the lower activation energy still showed a decrease in proton conduction resistance due to the multilayer structure.Specifically,the(PU/CNT-CdTe/PU/CS)150/60%PA membrane exhibited a maximum proton conductivity of 6.82×10-2 S/cm at 150℃.For the(PU/GO/PDDA/GO)200/60%PA membrane,a proton conductivity of 1.83×10-1 S/cm was obtained at 150℃.Further,the electrical conductivity was substantially stable 1.47×10-1 S/cm at 120℃ and 1.83×10-1 S/cm at 140℃.Polycation chitosan and polyanion graphene oxide were alternately deposited on the surface of SPVdF and SPVdF-HFP membranes by LBL technique.For the LBL self-assembled membranes of SPVdF-HFP(CS/GO)50 and SPVdF(CS/GO)50 that have good mechanical properties in this paper,the tensile properties E can reach 17.1 and 15.3 MPa,respectively.The conductivity values of SPVdF-HFP(CS/GO)50/85%PA and SPVdF(CS/GO)50/85%PA can reach 1.8×10-1 S/cm and 2.0×10-1 S/cm under anhydrous conditions at 140℃,and were decreased by about 10%after 500h at 140℃,maintaining a high conductivity.Therefore,the LBL self-assembly technique can provide a promising strategy for preparating multilayer membranes with membrane electrolytes.