Simultaneously enhancing proton conductivity and mechanical stability of the membrane electrolytes by crosslinking of poly(aromatic ether sulfone) with octa-amino polyhedral oligomeric silsesquioxane

Abstract

The trade-off between proton conductivity and mechanical property is a critical issue to phosphoric acid (PA) doped high temperature proton exchange membranes (HT-PEMs) for using as the electrolytes in various devices. Uniformly introducing additives into polymer matrix is required for improvements on the properties of the polymer membranes. Herein, the hydrophilic and acidophilic octa-amino polyhedral oligomeric silsesquioxane (OA-POSS) is synthesized for using as a filler and a crosslinker concurrently to prepare HT-PEMs based on poly(aromatic ether sulfone) (PAES). The PA doped membrane with a crosslinking degree of 10% exhibits a proton conductivity of 97.4 mS cm−1 at 180 °C without humidifying, and an enhanced tensile stress of 8.5 and 2.4 MPa under ambient atmosphere and 110 °C, respectively, which are about 60% and 70% higher than those of the pristine quaternary ammonium PAES membrane. A peak power density of 461 mW cm−2 is achieved by the membrane at 200 °C by fueling the fuel cell with non-humidified H2 and O2 without backpressure. Comprehensive characterizations on the structure, PA doping level, anhydrous proton conductivity, as well as dimensional stability and PA retention ability of the prepared membranes are made.