1. Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis, Singapore 138634, Singapore.
2. Department of Energy Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India.
3. Institute for Infocomm Research, Agency for Science, Technology and Research (A*STAR), 1 Fusionopolis Way, Connexis, Singapore 138632, Singapore.
4. The State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, and Center of Hydrogen Science, Shanghai Jiao Tong University, Shanghai 200240, P. R. China.
5. Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL 60439, USA.
6. Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.