Insight on Pure vs Air Exposed Hydroxide Ion Conductivity in an Anion Exchange Membrane for Fuel Cell Applications
FTIR-ATR spectra were collected using Nexus 4700 (Thermo-fisher) with an ATR accessory (Specac, Inc). A liquid nitrogen cooled mercury cadmium telluride (MCT) detector was used to collect a spectrum with 128 scans every 25 seconds with a resolution of 4 cm-1. A custom built design was used to control RH of the membrane sample during experiments. In order to verify the experimental setup, the diffusion coefficient of water through Nafion 117® membrane was observed at the same order of magnitude (1.63±0.27 x 10-7 cm2/s vs 3.71x 10-7 cm2/s observed by Elabd et al7) when the relative humidity of the sample was changed from 0 to 100 %RH. Water diffusion coefficient was then measured for AEMs as a function of temperature and RH. The Fickian water diffusion coefficient for AEMs was observed to be lower than proton exchange membranes by one order of magnitude. Figure 1 shows the comparison of water diffusion kinetics between one of the anion exchange membranes and Nafion 117® at 30 oC.
In this work, water behavior of different AEMs as a function of temperature and RH will be presented, the energy barrier for the water diffusion through these membrane will be discussed and the science behind a slow water diffusion through AEMs will be explored.
Figure 1. Time-resolved normalized absorbance for O-H stretching vibration collected using FTIR-ATR at 30oC when RH was increased from 0 to 100%.
The authors would like to thank the US Army Research Office for the funding under the MURI #W911NF-10-1-0520and the purchase of FTIR microscope from ARO DURIP #W911NFNF-0462
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