1. Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing 101400 P. R. China
2. School of Nanoscience and Technology University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. College of Materials and Metallurgy Guizhou University Guizhou 550025 P. R. China
4. Georgia Institute of Technology Atlanta GA 30332 USA
5. Shandong Zhongke Naneng Energy Technology Co., Ltd. Dongying 257061 P. R. China