Thermal Analysis and Cation Doping of Nafion Membranes

Cationic contamination degrades polymer electrolyte membrane fuel cell (PEMFC) performance by decreasing proton conductivity and water content in perfluorosulfonic membranes such as Nafion. Hydration of the membrane is important for cell durability and longevity; low relative humidity accelerates membrane degradation. Cations can exchange with the proton on the sulfonate group in the polymer and modify exchange site properties. In an effort to build upon the existing knowledge of polymer electrolyte membrane fuel cell (PEMFC) contamination effects, characterization of Nafion 117 and 212 in proton and sodium form has been performed. An emphasis has been placed on sodium because it is found in close proximity to automobiles on roads and marine environments, and in large enough quantities to potentially contaminate membrane materials. High diffusivity, thermal stability, and existing research make sodium an important cation. Cations Li+, K+, Cs+, Ca2+, Ni2+, and Cr3+ have been studied for comparison. Virgin and used gas diffusion layer (GDL), catalyst coated membrane (CCM), and uncatalyzed membrane (UCM) materials were examined to aid in single cell post-test characterization where separation of materials is difficult and may alter results. Through thermal analysis, FTIR, and vapor sorption the study shows how membranes of salt form differ in water content, freezable water, water cluster structure, water diffusion, and decomposition. Membranes of varying thickness in acid and sodium form have been tested in vapor sorption and FTIR for comparison