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 inperfluorosulfonic membranes such as Nafion. Hydration of the membrane is importantfor cell durability and longevity; low relative humidity accelerates membranedegradation. Cations can exchange with the proton on the sulfonate group in the polymerand modify exchange site properties.In an effort to build upon the existing knowledge of polymer electrolytemembrane fuel cell (PEMFC) contamination effects, characterization of Nafion 117 and212 in proton and sodium form has been performed. An emphasis has been placed onsodium because it is found in close proximity to automobiles on roads and marineenvironments, and in large enough quantities to potentially contaminate membranematerials. High diffusivity, thermal stability, and existing research make sodium animportant cation. Cations Li+, K+, Cs+, Ca2+, Ni2+, and Cr3+ have been studied forcomparison. Virgin and used gas diffusion layer (GDL), catalyst coated membrane(CCM), and uncatalyzed membrane (UCM) materials were examined to aid in single cellpost-test characterization where separation of materials is difficult and may alter results.Through thermal analysis, FTIR, and vapor sorption the study shows howmembranes of salt form differ in water content, freezable water, water cluster structure,water diffusion, and decomposition. Membranes of varying thickness in acid and sodiumform have been tested in vapor sorption and FTIR for comparison.