Impact of phase separation of polymeric proton exchange membranes on gas permeability for the fuel cell application
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1School of Chemical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran.
2Fuel Cell Laboratory, Green Research Center, Iran University of Science and Technology, Narmak, Tehran, Iran.
While high gas permeability is a requirement in some membrane industries, it is not considered advantageous in polymer electrolyte fuel cell (PEFC) application. Thus, proton exchange membranes are basically meant to be defect-free and dense. In this work, hydrogen cross-over rate and permeability values of state-of-the-art Nafion®117 and sulfonated poly(ether ether ketone) (SPEEK) membranes are measured by the volumetric method. In addition, surface characterization tests including field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) are performed in order to gain insight into their different gas permeation behavior. Results show that approximately three times higher H2 permeability value for Nafion membrane can be attributed to its well-defined phase separation. In other words, Nafion exhibits more homogenous hydrophilic micro-structure which has made it more susceptible to gas leakage in comparison with SPEEK membrane with randomly distributed phases.