Anion Exchange Composite Membranes Composed of Quaternary Ammonium-Functionalized Poly(2,6-dimethyl-1,4-phenylene oxide) and Silica for Fuel Cell Application

Abstract

Anion exchange membranes (AEMs) with good alkaline stability and ion conductivity are fabricated by incorporating quaternary ammonium-modified silica into quaternary ammonium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO). Quaternary ammonium with a long alkyl chain is chemically grafted to the silica in situ during synthesis. Glycidyltrimethylammoniumchloride functionalization on silica (QSiO(2)) is characterized by Fourier transform infrared and transmission electron microscopic techniques. The QPPO/QSiO(2) membrane having an ion exchange capacity of 3.21 meq.g(-1) exhibits the maximum hydration number (lambda = 11.15) and highest hydroxide ion conductivity of 45.08 x 10(-2) S cm(-1) at 80 degrees C. In addition to the high ion conductivity, AEMs also exhibit good alkaline stability, and the conductivity retention of the QPPO/QSiO(2)-3 membrane after 1200 h of exposure in 1 M potassium hydroxide at room temperature is about 91% ascribed to the steric hindrance offered by the grafted long glycidyl trimethylammonium chain in QSiO(2). The application of the QPPO/QSiO(2)-3 membrane to an alkaline fuel cell can yield a peak power density of 142 mW cm(-2) at a current density of 323 mA cm(-2) and 0.44 V, which is higher than those of commercially available FAA-3-50 Fumatech AEM (OCV: 0.91 V; maximum power density: 114 mW cm(-2) at current density: 266 mA cm(-2) and 0.43 V). These membranes provide valuable insights on future directions for advanced AEM development for fuel cells.