1. Department of Applied Physics, Research Institute for Smart Energy, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong 999077, China
2. The Key Laboratory of Fuel Cell Technology of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510641, China
3. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
4. Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan