1. Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2, Budapest 1117, Hungary
2. Erhvervsakademi Aarhus, Sønderhøj 30, 8260 Viby J, Denmark
3. Centre for Energy Research, Institute for Technical Physics and Materials Science, Konkoly-Thege M. út 29-33, Budapest 1121, Hungary