1. State Key Laboratory of Solidification Processing Center for Nano Energy Materials School of Materials Science and Engineering Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU) Xi'an 710072 P. R. China
2. School of Physical & Mathematical Sciences Nanyang Technological University 21 Nanyang Link Singapore 637371 Singapore
3. Department of Applied Physics The Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong P. R. China
4. Stephenson Institute for Renewable Energy Department of Chemistry University of Liverpool Crown Street Liverpool L69 7ZD UK
5. Gubkin University 65/1 Leninsky prospect Moscow 19991 Russia