Fuel Cell Proton Exchange Membrane Materials, Design And Development

Polymer exchange membrane fuel cells (PEMFCs) are called as fifth-generation fuel cell after AFC, PAFC, MCFC, SOFC. PEMFCs have widely applied in vehicles and portable devices as a promising new power sources because of the lowest working temperature, the fastest startup, the highest specific energy, low or zero emissions, which is thinked as a clean and high efficiency prouducing electric device in 21 century.As one of the key elements in a PEMFC system, a proton exchange membrane (PEM) is sandwiched between two platinum-porous catalytic electrodes (namely, an anode and a cathode) and functions as an electrolyte for transferring protons from the anode to the cathode as well as providing a barrier to the passage of electrons and to cross leakage of gas between the electrodes. Nowdays, typically used proton exchange membrane materials for PEMFC are perfluorinated copolymers (such as Nafion) because oftheir excellent mechanical properties and chemicalstability. However, very high cost, poor water managementcapability, and loss of proton conductivity at relatively high temperatures as well as high methanolpermeability limit their commercial development. Therefore, some researchers have focused on exploiting low cost and high performance proton exchange membrane.In this paper, Synthesis and preparation of proton exchange membrane with low cost and high permance for DMFC were designated to studied aim. A series of sulfonated poly(aryle ether krtone sulfone)s (SPAEKS) with different degree of sulfonation (DS) were synthesized via aromatic nucleophilic substitution copolymerization. The successful introduction of the sodium sulfonate groups into SPAEKS copolymers was confirmed by Fourier transform infrared (FTIR) spectroscopy. The high intrinsic viscosities of copolymers indicated that the copolymers had the high molecular weight and tough membranes were prepared by solution cast film. The synthesized sulfoanted copolymers showed good solubility in polarity solvent. TGA results indicated that the decomposition temperature of sulfonic acid groups in onset weight loss gradually decreased with increasing DS. Most importantly, all temperatures of weight loss are higher than 260℃, which could meet thermal request of PEMFC well. Moreover, the data of SPAEKS membranes performance indicated that with the increment of DS, water uptake, proton conductivity and methanol permeability increased, while the methanol diffusion coefficient decreased. Although the SPAEKS membrane show very good potential usages in DMFC, the SPAEKS membranes with high sulfonated degree have relatively high methanol crossover. This drawback should be solved for further application as PEM materials fuel cells, sulfonated poly(aryle ether ketone sulfone)/polypyrrole(SPAEKS/Ppy) composite membranes with different content of Ppy were prepared in chemical in-situ polymerization by means of ion-dipole interaction between the sulfonate groups of SPAEKS and amonium groups of polypyrrole. The incorporation of polypyrrole particles into the clusters, where was the transport pathway, could change the morphology of SPAEKS matrix. FTIR spectra suggested that the sulfonic acid groups on the copolymer backbone strongly interact with amonium groups of Ppy. SEM pictures showed that the Ppy particles were uniformly distributed not only present near the surface but also in the internal space of the SPAEKS membranes matrix. The composite membranes show good thermal stability, low water uptake, low Swelling ratio both at length and thickness and relatively high proton conductive capability. The methanol diffusion coefficient of SPAEKS/Ppy composite membrane is much lower than that of pure SPAEKS membrane, which suggested that the composite membranes are promising as proton exchange membranes for DMFC applications.To resolve the low proton conductivity of SPAEKS membrane at high temperature, a series of SPAEKS/TiO2 composite membranes with various DS and contents of TiO2 were successfully prepared by sel-gol method. The SEM picture of SPAEKS/TiO2 composite membranes exhibited that the TiO2 particles were homogeneously distributed in the membrane.and the diameters of TiO2 particles were around 100 nm. The water uptake of composite membranes increased with the content of TiO2 increasing at the same DS because of large specific surface area and high surface energy of TiO2 particle. The composite membranes displayed more thermal stability, higher pronton conductivity, lower methanol diffusion coefficient than those of SPAEKS membrane, which are potential for proton exchange membrane at elevated temperature operation.