Nitash Balsara, UC Berkeley

April 24, 2009 @ 9 am
Location: Carolyn Hoff Lecture Hall
Categories: Special Event

"Fuel Cell Membranes that become Wetter as the Surrounding Air Gets Hotter"

Abstract

We establish a new systematic methodology for controlling water retention of polymer electrolyte membranes (PEMs) at elevated temperatures. Block copolymer membranes comprising hydrophilic phases with widths ranging from 2 to 5 nm become wetter as the temperature of the surrounding air is increased at constant relative humidity. Simple calculations suggest that capillary condensation is important at these length scales. The widths of the moist hydrophilic phases were measured by cryogenic electron microscopy experiments performed on humid membranes and in-situ small angle neutron scattering. The connection between moisture content and proton conductivity is demonstrated. The talk will begin with a discussion of the thermodynamic properties of hydrated PEMs before discussing transport properties. We show that the thermodynamic properties of hydrated PEMs are not in agreement with standard theories of polymer/solvent mixtures.