1. Research Group of New Energy Materials and Devices, State Key Laboratory of Coal and CBM Co-Mining, North University of China, Taiyuan 030051, P. R. China
2. Institute of Traffic Engineering, Shanxi Vocational University of Engineering Science and Technology, Taiyuan 030051, P. R. China
3. State Key Laboratory of Coal and CBM Co-Mining, Jincheng 048012, P. R. China
4. State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, P. R. China