1. Fuel Cells and Solid State Chemistry Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark
2. Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
3. Institute of Physics, Chinese Academy of Sciences and Beijing National Laboratory for Condensed Matter Physics, 100190 Beijing, China
4. Plasma Physics and Technology Programme, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark