1. Institute of Energy & Environment Materials, School of Physics & Engineering, Sun Yat-Sen University, Guangzhou 510275, P. R.China; Guangzhou Institute of Chemistry, Chinese Academy of Sciences, P.O. Box 1122, Guangzhou 510650, People's Republic of China; and Department of Chemstry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec H3A 2K6, Canada