Hierarchical structure / property analysis of ETFE-based graft-type polymer electrolyte membranes

Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Yoshimura, Kimio; Oba, Yojiro*; Onuma, Masato*; Katsumura, Yosuke*; Maekawa, Yasunari

Fundamental understanding of the structure-property relationship of PEM is prerequisite for proper material design to improve PEM performance. In this work, we studied hierarchical structures of ETFE-based graft-type polymer electrolyte membranes using small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FE-SEM). Then the relationship between hierarchical structures and fuel cell properties of ETFE-PEM was explained. The membrane possesses a shoulder peak at low q range with d-spacing of 36.1 nm and new peak at high q range with d-spacing of 1.48 nm. Such peaks should be originated from lamellar structure and correlation distance of the sulfo groups in poly(styrene sulfonic acid) grafts, respectively. In FE-SEM images, the clear phase separation between hydrophobic and hydrophilic domains was observed.