1. Department of Materials Science, Institute of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
2. Corporate Research & Development Center, Toshiba Corporation, Kawasaki, Kanagawa 230-0024, Japan
3. Toshiba Energy Systems & Solutions Corporation, Kawasaki, Kanagawa 212-8585, Japan
4. Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
5. Tsukuba Research Center for Energy Materials Science (TREMS), University of Tsukuba, Ibaraki 305-8571, Japan