Measurement of water uptake in thin-film Nafion and anion alkaline exchange membranes using the quartz crystal microbalance

Abstract

a b s t r a c tWater uptake, sorption mechanics and swelling characteristics of thin-film Nafion and a commercially available Tokuyama alkaline anion exchange membrane ionomer from the vapour phase is explored using a quartz crystal microbalance (QCM). The water uptake measures the number of water molecules adsorbed by the ionomer per functional group and is determined in-situ using the QCM frequency responses allowing for comparison with nanogram precision. Crystal admittance spectroscopy, along with equivalent circuit fitting, is applied to both thin films for the first time and is used to investigate the ionomer's viscoelastic changes during hydration; to elucidate the mechanisms at play during low, medium and high relative humidities.

Effects of Humidity, Temperature and Bismuth Electrodeposition on Electroanalytical Performances of Nafion‐coated Printed Electrodes for Cd2+ and Pb2+ Detection

“…More precisely, proton conductivity typically increases with the RH% increment [9,10,13], as a consequence of the high water uptake which occurs in the Nafion thin film. In fact, it has been estimated that the number of water molecules for sulfonic acid group (λ) can vary between 0 and 25 for RH% from 0 to 100 %, respectively [43]. In addition, different RH%-dependent regimes were individuated for Nafion thin films [12,44].…”

Effect of humidity on the interaction of CO2 with alkaline anion exchange membranes probed using the quartz crystal microbalance

“…So to prevent any unwanted interaction with CO2 in air, the ionomer casting process was carried out in-situ and the experimental set-up was developed to preclude any unwanted CO2. The rig is shown in Figure 1(a) and further described in [31]. Mass spectrometry data has been used to confirm all seals are air-tight and to show no presence of any undesired air components.…”

“…The ionomer thickness ti was subsequently determined using the Sauerbrey Equation (7) and Equation 8 below [31]:…”

“…The quartz crystal microbalance (QCM) has previously been used to examine the effect of water uptake and change in viscoelastic properties of thin-film AAEMs [31]. Here it is applied to examine the effect of AAEM interaction with CO2 at different relative humidities.…”

“…The authors have previously described the hydration mechanisms in the AS-4 ionomer [31], the results of which are summarised by Figure 3(b). The findings suggest (through crystal admittance spectroscopy) that the ionomer initially undergoes a solvation period (< 66% RH) in which ion conducting channels begin to open, followed by swelling of these ionomer channels between 66% and 100% RH.…”