1 research outputs found
Effect of Elevated Temperatures on the States of Water and Their Correlation with the Proton Conductivity of Nafion
For
the first time, we report the effects of elevated temperatures,
from 80 to 100 °C, on the changes in the states of water and
ion–water channels and their correlation with the proton conductivity
of Nafion NR212, which was investigated using a Fourier transform
infrared spectroscopy study. Experimentally, three types of water
aggregates, protonated water (H<sup>+</sup>(H<sub>2</sub>O)<sub><i>n</i></sub>), nonprotonated hydrogen (H)-bonded water (H<sub>2</sub>O···H<sub>2</sub>O), and non-H-bonded water,
were found in Nafion, and the existence of those three types of water
was confirmed through ab initio molecular dynamics simulation. We
found that the proton conductivity of Nafion increased for up to 80
°C, but from 80 to 100 °C, the conductivity did not increase;
rather, all of those elevated temperatures showed identical conductivity
values. The proton conductivities at lower relative humidities (RHs)
(up to 50%) remained nearly identical for all elevated temperatures
(80, 90, and 100 °C); however, from 60% RH (over λ = 4),
the conductivity remarkably jumped for all elevated temperatures.
The results indicated that the amount of randomly arranged water gradually
increased and created more H-bonded water networks in Nafion at above
60% RH. From the deconvolution of the O–H bending band, it
was found that the volume fraction <i>f</i><sub><i>i</i> (<i>i</i>=each deconvoluted band)</sub> of H-bonded water for elevated temperatures (>80–100 °C)
increased remarkably higher than for 60 °C