Microstructure-Property Relationships in Sulfonated Polyether Ether Ketone/Silsesquioxane Composite Membranes for Direct Methanol Fuel Cells

• Published in: Journal of the Electrochemical Society 2014-01, Vol.161 (9), p.F815-F822
• Main Authors: Yun, Sukhwan, Parrondo, Javier, Zhang, Fan, Ramani, Vijay
• Format: Article
• Language: English
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.0021409jes

The synthesis, structural characterization, and performance evaluation of silsesquioxane - based sulfonated polyether ether ketone (SPEEK) composite membranes for direct methanol fuel cell (DMFC) applications are presented. 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS) was used as a silsesquioxane (SQO) precursor. Two batches of SPEEK membranes with ion exchange capacities (IEC) of 1.06 ± 0.02 meq/g (denoted by SPEEK11) and 1.34 ± 0.05 meq/g (denoted by SPEEK13) were prepared. The SQO loadings in the composite membranes ranged from 5 wt% to 30 wt%. The ionic conductivity of the SPEEK13 membrane (at 60°C) increased by up to 15 mS/cm (27%) upon incorporation of 15 wt% TPS-derived SQO, while the methanol permeability was at best slightly lowered (5-10%). The morphological changes in the composite membranes resulting from the introduction of SQO was studied by small angle X-ray scattering. The sharp decrease in conductivity with TPS loading was attributed to these changes in the membrane ionic domains. The performance of DMFCs with these SPEEK/SQO composite membranes was governed more by the proton conductivity than the methanol crossover. Compared to pristine SPEEK, the improved DMFC performance (at 60°C using air and 3M methanol) of SPEEK11+5 wt% TPS and SPEEK13+5 wt% TPS composite membranes (187 mA cm−2 and 240 mA cm−2 at 0.4 V, respectively) was observed.