Preparation technique of fuel cell membranes having sulfoalkyl ethers by radiation grafting and nucleophilic addition

Enomoto, Kazuyuki; Takahashi, Shuichi; Maekawa, Yasunari

The polymer electrolyte membranes consisting grafted sulfoalkyl ether on ETFE film were prepared. Grafting of vinyl acetate into the irradiated ETFE was carried out under Ar at 40 C. The grafting degrees increased with increasing an irradiation dose. The basic hydrolysis of poly(vinyl acetate) units in the grafting chain led to poly(vinyl alcohol) (PVA) in good yields. The sulfoalkylation of the hydroxyl group in the grafted PVA with 1,3-propanesultone was performed. A ring-opening reaction of 1,3-sultone induced by the nucleophilic addition of PVA gives sulfoalkyl ether in 70% yield. The ATR-IR spectrum of the membrane shows new peaks at 3369, 1647, and 1032 cm, which are assigned to sulfoalkyl ether. The SEM-EDS image of the membrane shows a homogenous distribution of S atoms. The ion exchange capacity and proton conductivity of the membrane are estimated to be 1.6 mequiv g and 0.12 S cm, which are high enough for a fuel cell application.