1. Department of Materials Science and Engineering, Faculty
of Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore
2. School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, P. R. China
3. School of Power Engineering, Chongqing University, Chongqing 400044, P. R. China
4. Beijing Synchrotron Radiation Facility, Institute of
High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China