Sulfonated poly(etheretherketone) based nanocomposite membranes containing POSS-SA for polymer electrolyte membrane fuel cells (PEMFC)

Abstract

Nanocomposite membranes were prepared using sulfonated polyhedral oligomeric silsesquioxane (POSS-SA) and incorporated into sulfonated polyetheretherketone (sPEEK) for their use in polymer electrolyte membrane fuel cells. The POSS-SA concentration was varied to investigate its effect on the nanostructure morphology, mechanical properties, proton conductivities, and cell performance of nanocomposite membranes. POSS-SA served as a plasticizer: The plasticizer effect of POSS-SA affected the formation of broadened proton-conducting nanochannels and enhanced the tensile strain of nanocomposite membranes. Tensile strain and yield modulus increased by 66.7% and 63.6%, respectively. Acidic POSS-SA served as a proton donor to sPEEK and increased the sPEEK nanochannel dimensions by 23%, leading to enhanced proton conductivities and cell performance. The highest proton conductivity and cell performance was achieved using 1.5 wt% of POSS-SA; these values decreased with > 1.5 wt% of POSS-SA, caused by the blocking of the nanochannels by POSS-SA aggregates. Compared with those observed for pristine sPEEK, the highest proton conductivity and maximum current density were 0.097 S/cm and 0.97 A/cm2, which were increased by 38.6% and 76.3%, respectively. Electrochemical impedance spectroscopy revealed that the superior cell performance with 1.5 wt% of POSS-SA is strongly related to the decreased interfacial resistance caused by expanded hydrophilic domains.