Journal
ELECTROCHIMICA ACTA
Volume 51, Issue 18, Pages 3699-3706Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2005.10.029
Keywords
sulfonated poly(ether ether ketone) (sPEEK); nafion; conductivity; pervaporation; pressure rise method; permeability coefficients; direct methanol fuel cell
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Homogeneous membranes based on sulfonated poly(ether ether ketone) (sPEEK) with different sulfonation degrees (SD) were prepared and characterized. In order to perform a critical analysis of the SD effect on the polymer barrier and mass transport properties towards direct methanol fuel cell species, proton conductivity, water/methanol pervaporation and nitrogen/oxygen/carbon dioxide pressure rise method experiments are proposed. This procedure allows the evaluation of the individual permeability coefficients in hydrated sPEEK membranes with different sulfonation degrees. Nafion((R)) 112 was used as reference material. DMFC tests were also performed at 50 degrees C. It was observed that the proton conductivity and the permeability towards water, methanol, oxygen and carbon dioxide increase with the sPEEK sulfonation degree. In contrast, the SD seems to not affect the nitrogen permeability coefficient. In terms of selectivity, it was observed that the carbon dioxide/oxygen selectivity increases with the sPEEK SD. In contrast, the nitrogen/oxygen selectivity decreases. In terms of barrier properties for preventing the DMFC reactants loss, the polymer electrolyte membrane based on the sulfonated poly(ether ether ketone) with SD lower or equal to 7 1 %, although having slightly lower proton conductivity, presented much better characteristics for fuel cell applications compared with the well known Nafion((R)) 112. In terms of the DMFC tests of the studied membranes at low temperature, the sPEEK membrane with SD = 71 % showed to have similar performance, or even better, as that of Nation((R)) 112. However, the highest DMFC overall efficiency was achieved using WEEK membrane with SD = 52%. 0 2005 Elsevier Ltd. All rights reserved.
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