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. Georgia Institute of Technology, Atlanta, Georgia 30332-0245, United States
4. Center on Nanoenergy Research, School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
5. Shandong Zhongke Naneng Energy Technology Co., Ltd., Dongying 257061, P. R. China