We have investigated the electrochemically triggered cycloreversion of quadricyclane (QC) to norbornadiene (NBD), a system that holds the potential to combine both energy storage and conversion in a single molecule. Unambiguous voltammetric traces are obtained for pure NBD and pure QC, the latter a strained polycyclic isomer of the former. The difference in redox potentials is smaller than the energy difference between the neutral molecules. This is owing to a significant energy difference between the corresponding radical cations, as demonstrated by density functional theory (DFT) calculations. The vibrational modes of each pure compound are characterized experimentally in the fingerprint region and identified by DFT methods. Thermal and electrochemical transformations of NBD and QC are monitored in situ by IR spectroelectrochemical methods. The kinetics of the cycloreversion of QC to NBD, which is catalyzed by oxidizing equivalents, can be controlled by an applied electrode potential, which implies the ability to adjust in real time the release of thermal power stored in QC.

We have performed a model study to explore the influence of surface structure on the anchoring of organic molecules on oxide materials. Specifically, we have investigated the adsorption of phthalic acid (PA) on three different, well-ordered, and atomically defined cobalt oxide surfaces, namely 1) Co₃O₄(111), 2) CoO(111), and 3) CoO(100) on Ir(100). PA was deposited by physical vapor deposition (PVD). The formation of the PA films and interfacial reactions were monitored in situ during growth by isothermal time-resolved IR reflection absorption spectroscopy (TR-IRAS) under ultrahigh vacuum (UHV) conditions. We observed a pronounced structure dependence on the three surfaces with three distinctively different binding geometries and characteristic differences depending on the temperature and coverage. 1) PA initially binds to Co₃O₄(111) through the formation of a chelating bis-carboxylate with the molecular plane oriented perpendicularly to the surface. Similar species were observed both at low temperature (130 K) and at room temperature (300 K). With increasing exposure, chelating mono-carboxylates became more abundant and partially replaced the bis-carboxylate. 2) PA binds to CoO(100) in the form of a bridging bis-carboxylate for low coverage. Upon prolonged deposition of PA at low temperature, the bis-carboxylates were converted into mono-carboxylate species. In contrast, the bis-carboxylate layer was very stable at 300 K. 3) For CoO(111) we observed a temperature-dependent change in the adsorption mechanism. Although PA binds as a mono-carboxylate in a bridging bidentate fashion at low temperature (130 K), a strongly distorted bis-carboxylate was formed at 300 K, possibly as a result of temperature-dependent restructuring of the surface. The results show that the adsorption geometry of PA depends on the atomic structure of the oxide surface. The structure dependence can be rationalized by the different arrangements of cobalt ions at the three surfaces.

Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst’s surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria “nanopocket”, which binds Pt²⁺ so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt-CeO₂ nanocomposites showing high Pt efficiency in fuel-cell catalysis we also identify these anchoring sites.

Towards a molecular understanding of the mechanism behind catalytic reforming of bioderived hydrocarbon oxygenates, we explore the CC bond scission of C₂ model compounds (acetic acid, ethanol, ethylene glycol) on ceria model catalysts of different complexity, with and without platinum. Synchrotron photoelectron spectroscopy reveals that the reaction pathway depends very specifically on both the reactant molecule and the catalyst surface. Whereas CC bond scission on Pt sites and on oxygen vacancies involves intermittent surface carbon species, the reaction occurs without any carbon formation and deposition for ethylene glycol on CeO₂(111).