Metal oxides as water retention materials for low humidity proton exchange membrane applications

Polymer electrolyte membrane fuel cells (PEMFCs) operating at elevated temperature have attracted considerable attention in recent years because they could benefit from enhanced tolerance to impurity of the fuel gas, improved water and heat management, and increased reaction rates at both cathode and anode compared with PEMFCs operating below 80oC. One of great technical challenges in high temperature PEMFC systems is proton exchange membranes (PEMs), which should maitain reasonable proton conductivity and good mechanical stability at high temperature. This has led researchers' interest to membranes impregnated with nano-structured hygroscopic metal oxides that can act as water retention materials in membranes. The incorporation of hydrophilic nanobuilding blocks of metal oxides as fillers comes in the form ofnanoparticles, nanowires, and nanotubes depending on the synthetic route and processing techniques. This chapter covers an unprecedented review of water retention and transport properties of metal oxides and metal oxide based materials for elevated temperature polymer electrolyte membrane. It provides an ideal introduction, preparations and characterization techniques as well as an overview of recent progress on metal oxide nanostructures and their applications as water retention materials for elevated temperature polymer electrolyte membranes.