Characterization of graft-type polymer electrolyte membranes at low grafting degrees for fuel cells

Abstract

Introduction: Proton exchange membrane (or polymer electrolyte membrane) fuel cells (PEMFCs) are attracting enormous research activities because they are a new power source for applications in different industrial sectors, such as transportation, stationaries, and portable devices. Nafion is the available commercial material for PEMs, but it has a high production cost, leading to a strong demand for alternative membranes. Polystyrene sulfonic acid (PSSA)-grafted poly(ethylene-co-tetrafluoroethylene) (ETFE) polymer electrolyte membranes (ETFE-PEMs) have been investigated extensively as alternative membranes for PEM fuel cells, but the results are mainly reported at grafting degrees (GDs) higher than 19%. Therefore, this study reports the results of thermal stability, mechanical strength, and proton conductivity for the ETFE-PEM with a low GD of 10%.

Methods: ETFE-PEM was prepared by radiation-induced grafting and subsequent sulfonation. The performance characteristics of ETFE-PEM related to fuel cells are investigated using thermal gravimetric analysis (TGA), mechanical testing, and electrochemical impedance spectroscopy.

Result: The ETFE-PEM shows higher or comparable mechanical strength and thermal stability to those of Nafion. In addition, ETFE-PEM can exhibit a conductance of 6.10-4–21.10-4 S/cm with a relative humidity (RH) of 40–60%, even at a very low GD of 10%.

Conclusion: ETFE-PEM shows better mechanical and thermal properties than Nafion and exhibits a rapid increase in conductance with RH of 40–60%, providing a potential application in PEM fuel cells for small devices such as motorcycles, mobile phones, or portable electronics.