High performance sulfonated poly(arylene ether phosphine oxide) membranes by self-protected cross-linking for fuel cells

Abstract

This work investigated the thermal treatment of sulfonated poly(arylene ether phosphine oxide) membranes under vacuum without using any cross-linking agents or additives. During the thermal treatment, the sulfonic acid groups of the membranes acted as cross-linkable groups and reacted with the activated benzene rings in the membranes, resulting in self-cross-linking. Interestingly, the available degree of cross-linking of the membranes almost no longer increased with increasing time and temperature after the required thermal treatment because many sulfonic acid groups of the membranes could not be cross-linked due to steric hindrance and only functioned as a conducting group of protons. Meanwhile, this approach facilitated the cross-linked membranes to exhibit excellent dimensional stability, as well as high proton conductivity. This is a self-protected cross-linking to some extent. Through such a cross-linking, phosphine oxide-containing membranes with excellent overall properties were achieved. In addition, this effect of steric hindrance could be employed to design cross-linked proton exchange membranes with high performance.