1. Guangzhou Key Laboratory for Surface Chemistry of Energy Materials; New Energy Institute; School of Environment and Energy; South China University of Technology; Guangzhou 510006 P. R. China
2. Analytical Instrumentation Center; Institute of Coal Chemistry; Chinese Academy of Sciences; Taiyuan 030001 P. R. China
3. School of Materials Science and Engineering; Georgia Institute of Technology; Atlanta GA 30332-0245 USA