Preparation And Characterization Of PPESK Ion Exchange Membrane By Electrospinning

As a new power plant, fuel cells have the advantages such as high energy conversion efficiency, fast start-up, zero pollution. As one of the core components of fuel cell, ion exchange membrane (such as proton exchange membrane and anion exchange membrane) is primarily separates cathode from anode and transfers H+/OH-. Its performance has a critical influence on the performance and lifetime of fuel cell.Perfluorinated sulfonic acid membranes (such as Nafion) are currently the commercial monopolies of proton exchange membranes (PEMs), however they have excessive methanol permeability, high cost, environment pollution when degradated and other shortcomings. The development of non-fluorinated membranes have also become academic focus. But the ion transport channels of non-fluorinated membrane are extremely narrow, discontinuous and more dead-ends. These problems have resulted in the conductivities of non-fluorinated membranes are lower than that of Nafion membranes. Compared with the PEMs, the basic functional groups of anion exchange membranes (AEMs) have lower dissociation constant and poorer activity, therefore electrical performances of AEMs are much inferior, which is urgently to be improved. Charged nanofibers which were produced by electrospinning and prepared ion exchange membranes could form continuous ion conductive channels in the membranes and efficiently transfer protons or hydroxyl ions. In this research, poly (phthalazinone ether sulfone ketone)(PPESK) was selected to prepare proton exchange membrane and anion exchange membrane containning electrospun fibers. Then the influences of charged fibers on electrical properties, mechanical and thermal stabilities of membranes were investigated, there are few reports about this at home and abroad.Firstly, sulfonated PPESK (SPPESK) nanofibers were prepared by electrospinning and the impacts of electrospinning conditions on SPPESK fiber diameters were investigated. With increasing concentration of solution, the viscosity of solution also increases, the morphologies of fibers varied from droplets or bead-fibers to continuous fibers, meanwhile the fiber diameters were increased. The most appropriate concentration of SPPESK was22.5wt%and the applied voltage was16kV.Further, according to the different solubilities of SPPESK in various solvents, SPPESK was used for filling the interfiber voids to prepare a series of SPPESK fiber membranes.The performances of SPPESK fiber membranes were optimized by changing DS of SPPESK fibers. The proton conductivity of DS104%/DS87%fiber membrane was186mS/cm at80℃, which was1.1times of DS104%cast membranes and higher than Nafion115(167mS/cm). In addition, the swelling ratio of the fiber membranes was30%, which was less than cast membrane. It indicated that the SPPESK fibers could not only improve the continuity of proton conductive channels and transfer proton effectively, but also restrict the swelling of membrane in water and increase the DS of proton exchange membrane to enhance conductivity.In this paper the preparation of anion exchange membranes were also explored by electrospinning method. Imidazolium-functionalized poly (phthalazinon ether sulfone ketone)(PPESK-ImCl) nanofibers were produced by electrospinning and the impacts of electrospinning conditions on PPESK-ImCl fiber diameters were investigated.With increasing concentrations of the spinning solution to18wt%, PPESK-ImCl fibers were varied from bead-fibers to continuous fibers. The highest conductivity of PPESK-ImOH cast membrane was20mS/cm when the DC increased at60℃. In order to increase the hydroxide conductivity, PPESK-ImOH/PSF-ImOH fiber membranes were prepared by filling with imidazolium-functionalized polysulfone (PSF-ImCl). The hydroxide conductivity of PPESK-ImOH/PSF-ImOH fiber membrane was30mS/cm at60℃, which was1.5times of PPESK-ImOH cast membrane.