Surface Modification of Heteropolyacids (HPAs) for Proton Exchange Membrane Fuel Cells (PEMFCs)

Novel composite proton exchange membranes have been prepared from surface modification of heteropolyacids, namely: silicotungstic acid (SiWA), and sulfonated poly(ether ether ketone) (SPEEK) as a polymer matrix. Atom transfer radical polymerization (ATRP) has been used for surface polymerization of sodium 4-vinyl benzene sulfonate (S4VBS) on SiWA. PEEK has been sulfonated using chlorosulfonic acid. The major outcome of this work was surface coated SiWA-poly(S4VBS) which resulted in homogenous composite membranes as compared with non-surface coated SiWA. The thermal properties of surface polymerized S4VBS have been characterized using differential scanning calorimetry (DSC). The SiWA particles and cross section of the composite membrane have been imaged using DSC. Composite membrane conductivity has been characterized using electrochemical impedance spectroscopy. This route was expected to provide a membrane with high conductivity because of the presence of sulfonic acid groups on the grafted polymer backbone, and to avoid "washing out" of HPA in the fuel cell.