1. Pillar of Engineering Product Development, Singapore University of Technology and Design, Singapore 487372, Singapore
2. School of Physics, Beihang University, Beijing 100191, P. R. China
3. Faculty of Materials and Manufacturing, Key Laboratory of Advanced Functional Materials, Education Ministry of China, Beijing University of Technology, Beijing 100124, P. R. China
4. Key Laboratory of Catalysis and Energy Materials Chemistry of Ministry of Education, Hubei Key Laboratory of Catalysis and Materials Science, South-Central University for Nationalities, Wuhan 430074, China