1. College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China
2. College of Electromechanical Engineering, Qingdao University of Science and Technology, Qingdao 266061, P. R. China
3. Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Shandong Energy Institute, Qingdao 266101, P. R. China