1. Fuel Cell Laboratory, Korea Institute of Energy Research, Daejeon 34129, South Korea
2. Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, United States
3. Fuel Cell Research & Demonstration Center, Korea Institute of Energy Research, Buan-gun, Jeollabuk-do 56332, South Korea
4. Department of Physics and Science of Advanced Materials Program, Central Michigan University, Mount Pleasant, Michigan 48859, United States
5. Unidad Académica de Física, Universidad Autónoma de Zacatecas, Zacatecas 98098, Mexico