Controlled Water Uptake in Fuel Cell Membranes with Dual Chemistry Confinement

Abstract

Nafion is one of the most commonly used materials for proton exchange membranes in polymer-electrolyte fuel cells (PEFC) due to its stability and high ion-transport capabilities. However, its dehydration problem as well as dimensional instability limits its application in high-temperature, low-humidity environments. In this paper, we propose a potential solution to this problem by introducing nanoscale confinements to the Nafion chains. In particular, a coarse grain molecular dynamics model is developed that reproduces the water absorption curve of the pristine Nafion membrane. The model enables us to perform systematic studies on the effects of confinement to the absorption behavior of the Nafion membrane at different activities. Confinement of different chemistries and sizes has been introduced in the simulation system in order to investigate its effects on water absorption on different activities. It is found that confinement of dual chemistry (consisting of both hydrophobic and hydrophilic confinements) offers a solution to its drawbacks. The hydrophobic confinement helps flatten the absorption curve and decrease the water absorption at high activity, while the hydrophilic confinement acts as a water reservoir, which increases the water absorption at low activity. The Nafion membrane with dual chemistry confinement in general has higher water absorption with smaller dimensional instability, which makes it suitable to operate in a high-temperature, low-humidity environment.