1. Department of Mechanical Engineering, Tufts University, Medford, Massachusetts 02155, United States
2. National Fuel Cell Research Center, University of California, Irvine, California 92697, United States
3. Department of Chemical and Biomolecular Engineering, University of California, Irvine, California 92697, United States
4. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States