Morphological characterization of grafted polymer electrolyte membranes at a surface layer for fuel cell application

摘要

The morphology and elemental compositions at the surface of poly(styrene sulfonic acid) (PSSA) grafted poly(ethylene-co-tetrafluoroethylene) polymer electrolyte membranes (ETFE-PEMs) in a grafting degree (GD) range of 0-127 are investigated by using FE-SEM and XPS analyses. The concentrations of elemental components at the surface are not a linear function of GDs, resulting from different grafting speeds at the surface and bulk. In addition, low accumulation of PSSA grafts on the surface of ETFE-PEMs in the low GDs of 0-19, as well as their homogeneous distribution through the membranes at least at a GD of 19 are observed. At higher GDs of 19-127, the PSSA accumulation on the surface is relatively limited, indicating the presence of more PSSA grafts inside the bulk than on the surface. The surface signatures of ETFE-PEMs over the entire GD range can be determined based on the grafting process. These interesting observations suggest the significant advantages of interfacial properties of ETFE-PEMs for fuel cell applications.