1. Center for Nanochemistry (CNC) Beijing Science and Engineering Center for Nanocarbons Beijing National Laboratory for Molecular Sciences College of Chemistry and Molecular Engineering Peking University Beijing 100871 P. R. China
2. Beijing Graphene Institute (BGI) Beijing 100095 P. R. China
3. State Key Laboratory of NBC Protection for Civilian Beijing 102205 P. R. China
4. Laboratory of Fuel Cells Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian 116023 P. R. China
5. Beijing Key Lab of Advanced Battery Materials Department of Materials Science and Engineering College of Engineering Peking University Beijing 100871 P. R. China
6. Electron Microscopy Laboratory and International Center for Quantum Materials School of Physics Peking University Beijing 100871 P. R. China