Modification of ultrathin polyetheretherketone film for application in direct methanol fuel cells

Chen, J.; Li, D.; Koshikawa, Hiroshi; Zhai, M.*; Asano, Masaharu; Oku, Hiroyuki*; Maekawa, Yasunari

An ultrathin polyetheretherketone (PEEK) film was modified by thermal grafting of divinylbenzene (DVB) followed by radiation grafting of ethyl styrenesulfonate (ETSS), to develop a polymer electrolyte membrane (PEM) for use in direct methanol fuel cells (DMFCs). The DVB-grafting yield by thermal polymerization was less than 7%, but was sufficient to enhance the subsequent ETSS-grafting. The ETSS units were converted to styrenesulfonic acid (SS) units by hydrolysis in hot water, resulting in an ultrathin PEEK-g-DVB-g-SS PEM. FT-IR and TG analysis as well as measurements for the ion exchange capacity, water uptake, proton conductivity, mechanical strength, and methanol permeability were performed. Furthermore, this new PEM was tested in a DMFC, and a high maximum power density was confirmed. Therefore, we conclude that this modified PEEK film can be used as the PEM for the application in DMFCs.