1. Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA
2. Department of Chemistry Technical University Munich Garching 85748 Germany
3. TUMint. Energy Research GmbH Lichtenbergstr. 4 Garching 85747 Germany
4. Department of Electrical and Computer Engineering Technical University Munich 80333 Munich Germany
5. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA 02139 USA