1. Department of Materials Science & Engineering/Fuel Cell Research Center, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
2. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
3. Department of Chemical Engineering, Auburn University, Auburn, Alabama 36849, United States
4. 1FCell Inc., Pohang 37673, Republic of Korea