Fabrication And Properties Of Durable-side-chain Grafted Proton Exchange Membrane

Proton exchange membrane (PEM) serving as electrolyte is one of the most critical components of proton exchang membrane fuel cells (PEMFCs). Currently, the most widely used polymer membrane in PEMFCs is perfluorinated sulfonic acid (PFSA) membrane (such as Nafion(?), produced by DuPont) which has been commercialized. However there are some obstacles hindering its widespread application in PEMFCs. For instance:i) the proton conductivity is strongly dependent on the water uptake, ii) the catalyst (pt) has poor tolerance to CO under low operating temperature, iii) high cost, pollution risk, high fuel crossover. Therefore it is necessary to improve the performance of PFSA or to exploit new-type PEM.In recent years researchers have been focusing on sulfonated hydrocarbon proton exchange membranes due to their high thermal stability, good mechanical stability and low cost. Graft copolymers, which contain sulfonic acid groups on side chains, are theoretically able to be used to produce membranes that possess highly concentrated, isotropically connectec ionic domains. Unfortunately, as a result of relatively immature technologies, many type graft copolymers are equipped with polystyrene side chains which are poorly stabilized.Traditional preparation of long side chain grafted polymer is achieved via graft polymerization of monomers with an unsaturated bond by radiation (UV, γ-rays,etc.) or atom transfer radical polymerization. This thesis presents a new method. We first made a sulfonated polyphenylene sulfide (sPPS) side chain, which was then grafted onto the polysulfone backbone with a chemical modification method. The PPS side chain has high thermal and chemical stability because of its aromatic structure, which contains sulfur atoms linked with the benzene ring in the para position. Such a side chain may form a large π bond structure. Polysulfone (PSf), which also has high thermal stability and excellent chemical stability, serves as main chain after chloromethylation. For comparison purpose, we also fabricated proton exchange membranes of polysulfone with sulfonated polystyrene (sPS) side chain.Our study shows that the proton conductivity of PSf-g-sPPS membrane increases as temperature goes up. Also, at the same temperature, the proton conductivity of membrane increases as grafting degree of PSf-g-sPPS ascends. At 80 ℃, the water uptake of PSf-g-sPPS membranes is 40.92%, and the swelling ratio is 21.3±0.85%, and the proton conductivity is 62 mS cm-1, showing its the potential of application in high temperature PEMFCs. The oxidation stability of PSf-g-sPPS is superior to that of PSf-g-sPS. The weight loss of PSf-g-sPPS and PSf-g-sPS increases with increasing treatment time, and the mass loss of PSf-g-sPPS is less than that of PSf-g-sPS’s. In terms of thermal stability, the temperature of PSf-g-sPPS complete degradation is higher than that of PSf-g-sPS complete degradation, and we can find the degradation rate of PSf-g-sPPS is slower than the degradation rate of PSf-g-sPS from the thermogravimatic analysis.This thesis provides a new method to prepare high performance proton exchange membrane, and is of importance for the development of proton exchange fuel cell.