Membrane/electrode assembly employing sulfonated aromatic polymers for polymer electrolyte fuel cells and their long-term stability

Abstract

Polymer electrolyte fuel cells (PEFCs) have been developed to produce efficient and environmentally friendly energy for stationary, transportation, and portable applications. In PEFCs, to substitute for Nafion membrane, numerous alternative membranes have been proposed and most of them are sulfonated aromatic polymer membranes. However, sulfonated aromatic polymer exhibits poor compatibility with Nafion and therefore the system composed of hydrocarbon membrane and Nafion-based electrode shows poor interfacial stability. In addition, the high IEC of sulfonated aromatic polymer results in much water uptake and such membranes exhibit poor dimensional stability because of polymer expansion by hydration. This thesis covered several strategies done last few years to alleviate or eliminate these disadvantages of sulfonated aromatic polymer membrane. In Chapter II, as the effort to improve the compatibility between membrane and electrode, sPEEK ionomer was introduced as the electrode binder. The electrode ionomer is a key component of the catalyst layer and therefore the introduction of new electrode ionomer would have a significant effect on cell performance. To investigate the effect of sulfonated poly(ether ether ketone) (sPEEK) as the electrode ionomer, the catalyst layer was prepared using sPEEK ionomer and its physical properties such as pore structure and the hydrophobicity were examined. The electrochemical characteristics of the membrane and electrode assemblies employing sPEEK ionomer-based catalyst layer were also analyzed. Even though sPEEK ionomer-based catalyst layer showed lower ohmic resistance compared with Nafion ionomer-based catalyst layer, complete pore-filling of sPEEK into the primary pore caused reduction in reactive surface area of the catalyst and hindrance in gas transfer. In addition, the very low hydrophobicity of sPEEK ionomer-based catalyst layer deteriorated gas transfer due to an increased water flooding. To adopt Nafion binder havi...