Sulfonated poly(ether sulfone) (SPES)/boron phosphate (BPO 4) composite membranes for high-temperature proton-exchange membrane fuel cells

Abstract

A new series of sulfonated poly(ether sulfone) (SPES)/boron phosphate (BPO 4) composite membranes for proton-exchange membrane fuel cells (PEMFCs) applications, with a BPO 4 content up to 40 wt%, were prepared by a sol–gel method using tripropylborate and phosphoric acid as precursors. Compared to a pure SPES membrane, BPO 4 doping in the membranes led to a higher thermal stability and glass-transition temperature ( T g) as revealed by TGA–FTIR, DSC and DMTA. Water uptake and oxidative stability were significantly increased by increasing the content of BPO 4. At both operating temperature conditions, namely 20 °C and 100 °C, the tensile strength of all the composite membranes were lower than that of the SPES membrane. However, even when the content of BPO 4 was as high as 30%, the composite membrane still possessed strength similar to the Nafion 112 membrane. SEM–EDX indicated that the BPO 4 particles were uniformly embedded throughout the SPES matrix, which may facilitate proton transport. Proton conductivities increased from 0.0065 to 0.022 S cm −1 at room temperature as BPO 4 increased from 0 to 40%. The conductivities also increased with the temperature. The SPES/BPO 4 composite membrane is a promising candidate for PEMFCs applications, especially at higher temperatures.