1. Center
for Energy Convergence Research, Korea Institute of Science and Technology, Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea
2. Korea University of Science and Technology, 217 Gajeong-ro Yuseong-gu, Daejeon 305-333, Republic of Korea
3. Department
of Energy and Materials Engineering, Dongguk University-Seoul, Seoul 100-715, Republic of Korea