Elucidating the impact mechanism of temperature and water content on thermal conductivity of hydrated Nafion membranes by molecular dynamics simulation

Abstract

The thermal conductivity of the proton exchange membrane significantly affects the operating performance of the fuel cell. In this work, the impact of water content and temperature on thermal conductivity of hydrated Nafion membranes was investigated via molecular dynamics simulations and the influencing mechanism was explained from the perspective of interchain and intrachain heat transfer. The study shows that the thermal conductivity is mainly positively affected by water content, which is a result of the triple effect of hydrogen bonding acting as interchain heat transfer bridge, the stronger microphase separation allowing water to behave more like bulk water, and the decrease in the degree of chain torsion resulting in less phonon scattering along the chain. Particularly, we emphasized two crucial paths in which hydrogen bonding improves interchain heat transport. Furthermore, the temperature has little and slightly negative effects on thermal conductivity at low and high hydration levels, respectively. That is because, in low hydration levels, the incomplete hydrogen bond network is hardly influenced, but the bridging effect is suppressed and intrachain heat transfer capacity is reduced in high hydration levels. We believe this study can broaden the design basis of high temperature polymer electrolyte membranes.