In-situ observation of an anion exchange membrane at various humidity by X-ray scattering

[Display omitted] •In-situ observation of QPAF-4 was performed under various humidity conditions by synchrotron X-ray scattering measurements.•Hysteresis of the adsorption and desorption processes of water vapor to the membrane is observed.•The information of hydrogen bonding interaction in the membrane at various humidity conditions is obtained.•In-situ observation in the present study clarified the humidity dependence of the bonding state of water in the membrane. In-situ observation of an anion exchange membrane (AEM), QPAF-4, synthesized by the group of University of Yamanashi, was performed under various humidity conditions by synchrotron X-ray scattering measurements. The absorption process of water vapor into the AEM was slow, taking even a few hours. When the environmental humidity decreased, the amount of water contained in the membrane decreased also very slowly. Hysteresis was clearly observed during the absorption and desorption processes. Although the amount of absorbed water was very small, a meaningful difference in the X-ray scattering intensity was found between water-absorbed and dry membrane. The radial distribution functions (RDFs) of the membrane under various humidity conditions were obtained by subtracting the scattering of the chamber, where the humidity and the temperature were contorted from the scattering intensity from the membrane in the chamber. The peak at 2.8 Å was assigned to the hydrogen bonding interaction of O(water)-O(water) and non-hydrogen bonded interaction of water molecules. These peaks increased under a high humidity condition. In-situ observation in the present study clarified the humidity dependence of the bonding state of water in the AEM.