1. Department of Chemical and Biomolecular Engineering, University of Nebraska—Lincoln, Lincoln, Nebraska 68588, United States
2. Nebraska Center for Materials and Nanoscience, Voelte-Keegan Nanoscience Research Center, University of Nebraska—Lincoln, Lincoln, Nebraska 68588-0298, United States
3. 3M Fuel Cell Components Program, 3M Company, St. Paul, Minnesota 55144, United States