| Proton exchange membrane (PEM) is the core component of PEMFC, of which the cost and properties are both the most important problems. Our research works were outspread around the two sixty-four-dollar questions:In order to reduce the cost of PEM, the low-cost styrene - butylenes/ethylene -styrene (SEBS) three blocks copolymer was chosed as the elementary materials. SEBS was sulfonated with the premixing method, and then sulfonated SEBS(S-SEBS) membranes were successfully prepared by the method of solution casting. The sulfonic groups determined by a FT-IR are just on the para-positions of phenyls of PS blocks. It was also found that Sulfonation degree exerted great influence on the properties of S-SEBS membranes. The conductivity, water uptake, swelling and hydration coefficient all increase drastically when sulfonation degree comes to 15 percent, when the microstructure of membranes was abruptly changed, and a ionic channel being propitious to the proton conductivity was formed. Then the first three keep increasing growing and gradually become slow when the sulfonation degree reached 30% due to the spatially domino offect. The thermal stability of SEBS was decreased after being sulfonated by TG analysis, and the higher the sulfonation degree reached, the lower the thermal stability was, but it still retains about 150℃, which could also satisfy the requirement of PEMFC. The chemical stability of S-SEBS in high temperature was bad while in lower temperature about 40 ℃ was better, so S-SEBS might be of a wider foreground in low temperature PEMFC. Proton conductivity of S-SEBS reached 0.048 S/cm, the single cell power attained 0.147 W/cm2, which can satisfy the demand of lower power PEMFC, but S-SEBS swell excessively(swelling was 80% when the water uptake was 40% )and the strength of S-SEBS was of a sort.(especially wet membranes, only about 10Mpa).In order to reduce the swelling and increase the strength of S-SEBS, the simple cross-linking method was advanced in this article, and the proton conductivity was expected to remain higher. Being cross-linked can reform swelling excessively and bad strength, which was shown by the cross-linking reaction caused by the excessive acetic anhydride. Through FT-IR and performance analysis, it was found that sulfonic groups were cross-linked activated by the excessive acetic anhydride, by which swelling decreased and strength of membranes improved. Due to this, S-SEBSmembranes were lightly cross-linked through condensation of sulfonic acid groups with bis(4-aminophenyl)sulfone and l,l'-carbonyldiimidazole to form sulfonamide linkages in this paper. It was found that the cross-linking reaction was successful proved by FT-IR and performances analysis. Because the influence of side reaction and the spatially domino offect, the factual values of cross-linking degree were lower than the theoretic values. So as to attain higher conductivity, the cross-linking degree should be controlled in the lightly cross-linking scope (<10%) . The properties of cross-linked S-SEBS were better when the cross-linking degree reached 5%. The Strength of the membranes were highly enhanced by lightly cross-linked while little influence was exerted on proton conductivity, the cross-linked membranes were found to swelling 60 percent lower and absorb 40 percent less water than noncross-linked membranes. And the thermal and chemical stability of S-SEBS were both improved after being cross-linked, the Methanol resist properties was also increased. Although the Fuel Cell performance was decreased slightly, the maximal power density was reduced from 0.147 W/cm2 to 0.128 W/cm2, as far as it is concerned, the general properties of S-SEBS was advanced to the long-time work for PEMFC.Cross-linking method was successful applied in the modifications of S-SEBS membranes, which is not only enrich the preparation technology of PEM, but also has important significance to modify performance, reduce the cost and promote the commercial application of Fuel Cell.
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