Properties and Morphologies of Anion-Exchange Membranes with Different Lengths of Fluorinated Hydrophobic Chains

Yuto Shirase; Akinobu Matsumoto; Kean Long Lim; Donald A Tryk; Kenji Miyatake; Junji Inukai

doi:10.1021/acsomega.1c06958

Properties and Morphologies of Anion-Exchange Membranes with Different Lengths of Fluorinated Hydrophobic Chains

ACS Omega. 2022 Apr 12;7(16):13577-13587. doi: 10.1021/acsomega.1c06958. eCollection 2022 Apr 26.

Authors

Yuto Shirase¹, Akinobu Matsumoto², Kean Long Lim³, Donald A Tryk², Kenji Miyatake^{2

4

5}, Junji Inukai^{2

3

4}

Affiliations

¹ Integrated Graduate School of Medicine, Engineering, and Agricultural Sciences, University of Yamanashi, 4-4-37 Takeda, Kofu, Yamanashi 400-8510, Japan.
² Fuel Cell Nanomaterials Center, University of Yamanashi, 6-43 Miyamae-cho, Kofu 400-0021, Japan.
³ Fuel Cell Institute, Universiti Kebangsaan Malaysia, Bangi, Selangor 43600, Malaysia.
⁴ Clean Energy Research Center, University of Yamanashi, 4-3-11 Takeda, Kofu 400-8510, Japan.
⁵ Department of Applied Chemistry, Waseda University, Tokyo 169-8555, Japan.

Abstract

An anion-exchange electrolyte membrane, QPAF(C6)-4, polymerized with hydrophobic 1,4'-bis(3-chlorophenyl)perfluorohexane and hydrophilic (6,6'-(2,7-dichloro-9H-fluorene-9.9-diyl)bis(N,N-dimethylhexan-1-amine) is physically flexible and chemically stable. The drawbacks are relatively large water swelling and lower OH^- conductivity at higher water uptakes, which are considered to be due to the entanglement of the flexible hydrophobic structure of the membrane. In this study, a QPAF(C4)-4 membrane was newly synthesized with shortened hydrophobic fluoroalkyl chains. Unexpectedly, QPAF(C4)-4 showed a higher water uptake and a lower bulk/surface conductivity than QPAF(C6)-4 possibly due to the decrease in hydrophobicity with a smaller number of fluorine atoms. The thermal stability of QPAF(C4)-4 was higher than that of QAPF(C6)-4, possibly due to the rigidity of the QAPF(C4)-4 structure. A higher mechanical strength of QAPF(C6)-4 than that of QPAF(C4)-4 could be explained by the larger interactions between molecules, as shown in the ultraviolet-visible spectrum. The interactions of molecules were understood in more detail with density functional theory calculations. Both the chemical structures of the polymers and the arrangements of the polymers in the membranes were found to influence the membrane properties.