1. Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, United States
2. Department of Chemical Engineering, Columbia University, New York, New York 10027, United States
3. Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, United States
4. Fuel Cell Laboratory, Korea Institute of Energy Research, Daejeon 305-343, South Korea