1. School of Energy and Power Engineering, Chongqing University, Chongqing 400044, P. R. China
2. Key Laboratory of Low-Grade Energy Utilization, Technologies and Systems of Ministry of Education, Chongqing University, Chongqing 400044, P. R. China
3. Chongqing Institute of Graphene, Chongqing 404100, P. R. China