Anion Transport in a Chemically Stable, Sterically Bulky α‑C Modified Imidazolium Functionalized Anion Exchange Membrane

• Published in: Journal of physical chemistry. C Vol. 118; no. 28; pp. 15136 - 15145
• Main Authors: Liu, Ye, Wang, Junhua, Yang, Yuan, Brenner, Thomas M, Seifert, Söenke, Yan, Yushan, Liberatore, Matthew W, Herring, Andrew M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.07.2014
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp5027674

The morphology and anion transport of an α-C modified imidazolium functionalized anion exchange membrane, 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl)imidazolium functionalized polyphenylene oxide (with ion exchange capacity {IEC} = 1.53 or 1.82 mequiv/g), were studied in detail. The novel cation is less susceptible to OH– attack (0% degradation) compared to unsubstituted imidazolium functionalized polyphenylene oxide (25% degradation) after 24 h at 80 °C in 1 M KOH. The two different IEC materials (with the same protected cation) show interesting differences in membrane performance. From AFM and SAXS under humid conditions, the domain sizes of the membrane change, which impact the transport properties. The lower IEC sample showed a smaller tortuosity and, thus, needs a longer diffusion time for the water molecules to be fully hindered inside the hydrophobic clusters, which is confirmed by water self-diffusion measurements from pulsed field gradient NMR. From conductivity and diffusion measurements, the higher IEC sample exhibited Vogel–Tammann–Fulcher behavior, thus indicating that the polymer chain’s movement dominates the transport. However, the lower IEC sample exhibited the linear Arrhenius behavior signifying water-mediated transport. The maximum Cl– conductivity observed was 23 mS/cm at 95% RH and 90 °C.