1. Department of Chemical and Materials Engineering, University of Alberta, 9211-116 Street NW, Edmonton, Alberta T6G 1H9, Canada
2. Fuel Cell Research and Demonstration Center, Future Energy Research Division, Korea Institute of Energy Research, 20-41, Sinjaesaengeneogi-ro, Haseo-myeon, Buan-gun, Jeollabuk-do 56332, Republic of Korea
3. School of Materials Science and Engineering, Gwangju Institute of Science and Technology, 261 Cheomdan-gwagiro, Gwangju 500-712, Republic of Korea