Sulfonated Polyphenylene-Based Multiblock Membranes with Fluorine Moiety for Fuel Cell Applications

Abstract

Sulfonated poly(phenylene-co-arylene ether sulfone) multiblock copolymers are synthesized via Colon’s nickel-mediated cross-coupling reaction and are investigated as a proton-exchange membrane fuel cell. To investigate the influence of the fluorine moieties on the membrane properties, two different membranes are prepared, one containing a fluorinated hydrophobic poly(arylene ether) block (6F polymer membrane) and a nonfluorinated biphenyl (BP) polymer membrane. The proton transport, morphology, mechanical properties, and oxidative stabilities of the membranes are examined in relation to the ion-exchange capacity (IEC). 6F polymer membranes show superior proton conductivity and oxidative stability (results of Fenton’s oxidative stability and hydrogen peroxide exposure tests) compared with the BP polymer membranes. In water at 25°C, 6F and BP polymer membranes with IEC 2.0 meq g–1 exhibit proton conductivity of 0.11 S cm–1 with 6F having 16% lower water uptake than BP polymer. Meanwhile, at 30% RH and 80°C, 6F-X5Y9-(2.0) exhibits proton conductivity of 0.0026 S cm–1 that almost 50% higher than BP-X5Y7-(2.0) with 0.0018 S cm–1, while at 90% RH and 80°C, both polymers have an almost similar value of 0.10 S cm–1. Oxidative stability with the Fenton test under harsh conditions demonstrates that 6F-X5Y9-(2.0) has an extent degradation of 26%, almost 19% lower than BP-X5Y7-(2.0) with 32%, and the hydrogen peroxide exposure test demonstrates that 6F has 50% lower extent of degradation than BP with 5 and 9%, respectively. Fuel cell performance test at 80°C and 100% RH show that 6F-X5Y9-(2.0) exhibits a current density of 1.6 A cm–2 at 0.6 V (hydrogen/air) and outperforms Nafion-NR211 and BP-X5Y7-(2.0), 1.4 A cm–2 and 1.2 A cm–2, respectively. Undoubtedly, incorporating fluorinated moieties could enhance proton transport properties and oxidative stability favorable for fuel cell application.