| AVS 65th International Symposium & Exhibition | |
| Surface Science Division | Wednesday Sessions |
| Session SS+AS+EM-WeA |
| Session: | Semiconducting Surfaces |
| Presenter: | Jörg Libuda, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany |
| Authors: | M. Schwarz, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany F. Waidhas, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany C. Schuschke, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany S. Mohr, Friedrich-Alexander-Universität Erlangen-Nürnberg O. Brummel, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany T. Döpper, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany C. Weiss, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany K. Civale, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany M. Jevric, Chalmers University of Technology, Gothenburg, Sweden J. Bachmann, Friedrich-Alexander-Universität Erlangen-Nürnberg. Germany A. Görling, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany A. Hirsch, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany K. Moth-Poulsen, Chalmers University of Technology, Gothenburg, Sweden J. Libuda, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany |
| Correspondent: | Click to Email |
Photochemical isomerization of small organic molecules enables chemical energy storage via a single-photon-single-molecule process. A prototypical example is the conversion of norbornadiene (NBD) to its strained metastable valence isomer quadricyclane (QC), which releases up to 100 kJ/mol upon cycloreversion. This makes the NBD-QC system a solar fuel with an energy density comparable to state-of-the-art batteries.
In order to obtain a better understanding of NBD-based energy storage systems, we studied both the photochemical conversion and the catalytically and electrochemically triggered back-conversion at atomically defined interfaces. We combined vibrational spectroscopy with in-situ photochemistry in ultrahigh vacuum (UHV) and in electrochemical (EC) environments. In UHV, NBD and QC films were grown by physical vapor deposition (PVD) on Pt(111). By infrared refection absorption spectroscopy (IRAS), we observe spontaneous cycloreversion in QC monolayers even at 130 K, while QC multilayers are stable. Adsorbed NBD adopts a η2:η1 geometry which involves an agostic C-H-Pt interaction. At 300 K, this species undergoes dehydrogenation by splitting off the agostic H.
In UHV environments, the conversion from NBD to QC can be triggered in-situ by UV light and a co-deposited photosensitizer (PS). In electrochemical environments, back-conversion can be triggered by the electrode. On Pt(111) electrodes, we monitored the back-conversion in-situ by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS). The corresponding spectra were analyzed based on simulated spectra from density functional theory (DFT). Using a new photoelectrochemical IRRAS setup (PEC-IRRAS), we monitored the complete storage and release cycle by in-situ vibrational spectroscopy. Selectivities were determined both for the conversion and the back-conversion, showing that the stability of the PS is a critical step in the storage cycle. Much higher reversibility could be obtained using new NBD derivatives which avoid an additional PS.
To better control the energy transfer via the electrode interface, we investigated NBD derivatives anchored via a carboxylic-acid function to atomically defined oxide surfaces. In UHV, dense monolayers of surface-anchored NBD derivatives were prepared by PVD onto Co3O4(111) films on Ir(100). The molecules adopt an upright-standing orientation with the NBD units pointing away from the interface. Finally, we explored the behavior of these films in (photo)electrochemical environments.
[1] O. Brummel et al., ChemSusChem 9, 1424 (2016).
[2] U. Bauer at al., Chem. Eur. J. 23, 1613 (2017).
[3] O. Brummel et al., J. Phys. Chem. Lett., 8, 2819 (2017).