1. State Key Laboratory of Control and Simulation of Power Systems and Generation Equipments, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China
2. Department of Chemistry and Biochemistry, University of South Carolina, 541 Main Street, Horizon I Room 232, Columbia, South Carolina 29208, USA
3. Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, 110 8th Street MRC 140, Troy, New York 12180, USA