Zirconium silicate-ionic liquid membranes for high-temperature hydrogen PEM fuel cells

Abstract

Proton exchange membranes (PEMs) based on zirconium silicate (ZrSi) and ionic liquids (ILs) for the application in high-temperature fuel cells are reported in this work. The proton conductive material (ZrSi/ILs) was supported on porous polytetrafluoroethylene (PTFE). Several mass ratios of ZrSi/ILs were investigated. 1-Hexyl-3-methylimidazolium tricyanomethanide [HMIM][TCM] and 1-butyl-3-methylimidazolium thiocyanate [BMIM][SCN] ILs were used in this study. The membranes were characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The synthesized composite membranes demonstrated high proton conductivity in the range of 0.1–0.2 S/cm at 25 °C, exceeding that of Nafion (0.01 S/cm). Furthermore, the synthesized composite membranes were processed at a high temperature (200 °C), and exhibited a high proton conductivity of 0.001 S/cm. Thermogravimetric analysis (TGA) demonstrated a slight weight loss of around 200 °C and an approximately 18% weight loss at around 500 °C for the synthesized membrane. SEM illustrated the formation of very small crystalline particles within the confined pores of PTFE, upon the addition of ILs. Water uptake analysis revealed that the composite membranes in this study could hold water by more than 50% by weight. The results showed enhanced proton conductivities that can be attributed to the enhanced water uptake and the presence of multiple proton-conducting paths within the membrane matrix.