Permeability and Diffusivity Measurements on Polymer Electrolyte Membranes

An essential material property directly influencing the long-life capacity of hydrogen-polymer electrolyte membrane fuel cells (H2-PEMFCs) systems at elevated temperatures (>80 degrees C) is the permeability of the PEM material toward gases. The membrane permeability with respect to hydrogen and oxygen is responsible for a decrease of fuel cell efficiency and life-time. Furthermore permeating oxygen is suspected to form membrane degrading O-radical species. In view of the importance of gas permeability for further PEM R&D activities we present a test bench for the experimental determination of gas diffusivities and permeabilities for such polymeric materials. The advantages of a direct coupling of the permeation measurement cell with a gas chromatograph as analyzer are outlined. Hydrogen and oxygen diffusivities as well as permeabilities of prospective new materials such as cross-linked SPEEK are determined at different temperatures and are compared to state-of-the-art PFSA material. A significantly lower permeability regarding hydrogen and oxygen was determined for cross-linked SPEEK materials. In addition the influence of the hydro-thermal history of PFSA materials, postulated by G. Alberti, on membrane diffusivity was studied.