TY - JOUR
T1 - Hydrogen Permeation in Hydrated Perfluorosulfonic Acid Polymer Membranes
T2 - Effect of Polymer Crystallinity and Equivalent Weight
AU - Takeuchi, Kotono
AU - Kuo, An Tsung
AU - Hirai, Takeshi
AU - Miyajima, Tatsuya
AU - Urata, Shingo
AU - Terazono, Shinji
AU - Okazaki, Susumu
AU - Shinoda, Wataru
N1 - Funding Information:
This research was supported by the Impulsing Paradigm Change through Disruptive Technologies (ImPACT) program and by MEXT as a social and scientific priority issue (“Development of New Fundamental Technologies for High-efficiency Energy Creation, Conversion/Storage, and Use”) to be tackled using the post-K computer. Calculations were performed on the facilities of the supercomputer center at Nagoya University; Research Center for Computational Science, Okazaki; the Institute for Solid State Physics, the University of Tokyo; and, in part, on the K-computer hosted at the RIKEN Advanced Institute for Computational Science (Proposal No. hp180209 and hp180231).
Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/8/22
Y1 - 2019/8/22
N2 - Gas permeation through proton exchange membranes affects a fuel cell's electrochemical performance. To understand the gas permeation mechanism, gas permeability and wide-angle X-ray diffraction were measured for different equivalent weight (EW) perfluorosulfonic acid (PFSA) membranes at different water uptakes. A series of molecular dynamics (MD) simulations were also conducted. Through MD simulation, water sorption effects were found to result from an increased probability of dissolved H2 molecules being near the water phase, where a higher H2 diffusivity was observed. Furthermore, the local semicrystalline structure of the PFSA polymer and the morphology of the water clusters in the membrane were found to affect H2 permeation in the high- and low-EW PFSA membranes, respectively. For the high-EW (EW > 909) membranes, the presence of the local crystalline structure decreased the void fraction in the structure and inhibits the H2 diffusion across the aligned polymer chains. This effectively reduced H2 solubility and diffusivity, thereby reducing H2 permeability. The low-EW membranes contained a lower number of PTFE regions and exhibited a highly tortuous network in the aqueous domain. The former contributed to a reduction in H2 solubility and the latter reduced the H2 diffusivity. Therefore, H2 permeability decreased with a decreased EW.
AB - Gas permeation through proton exchange membranes affects a fuel cell's electrochemical performance. To understand the gas permeation mechanism, gas permeability and wide-angle X-ray diffraction were measured for different equivalent weight (EW) perfluorosulfonic acid (PFSA) membranes at different water uptakes. A series of molecular dynamics (MD) simulations were also conducted. Through MD simulation, water sorption effects were found to result from an increased probability of dissolved H2 molecules being near the water phase, where a higher H2 diffusivity was observed. Furthermore, the local semicrystalline structure of the PFSA polymer and the morphology of the water clusters in the membrane were found to affect H2 permeation in the high- and low-EW PFSA membranes, respectively. For the high-EW (EW > 909) membranes, the presence of the local crystalline structure decreased the void fraction in the structure and inhibits the H2 diffusion across the aligned polymer chains. This effectively reduced H2 solubility and diffusivity, thereby reducing H2 permeability. The low-EW membranes contained a lower number of PTFE regions and exhibited a highly tortuous network in the aqueous domain. The former contributed to a reduction in H2 solubility and the latter reduced the H2 diffusivity. Therefore, H2 permeability decreased with a decreased EW.
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U2 - 10.1021/acs.jpcc.9b05502
DO - 10.1021/acs.jpcc.9b05502
M3 - Article
AN - SCOPUS:85071442992
SN - 1932-7447
VL - 123
SP - 20628
EP - 20638
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 33
ER -