6 research outputs found
Au-Catalyzed Energy Release in a Molecular Solar Thermal (MOST) System: A Combined Liquid-Phase and Surface Science Study
Molecular solar thermal systems (MOSTs) are molecular systems based on couples of photoisomers (photoswitches), which combine solar energy conversion, storage, and release. In this work, we address the catalytically triggered energy release in the promising MOST couple phenylethylesternorbornadiene/quadricyclane (PENBD/PEQC) on a Au(111) surface in a combined liquid-phase and surface science study. We investigated the system by photoelectrochemical infrared reflection absorption spectroscopy (PEC-IRRAS) in the liquid phase, conventional IRRAS and synchrotron radiation photoelectron spectroscopy (SRPES) in ultra-high vacuum (UHV). Au(111) is highly active towards catalytically triggered energy release. In the liquid phase, we did not observe any decomposition of the photoswitch, no deactivation of the catalyst within 100â
conversion cycles and we could tune the energy release rate of the heterogeneously catalyzed process by applying an external potential. In UHV, submonolayers of PEQC on Au(111) are back-converted to PENBD instantaneously, even at 110â
K. Multilayers of PEQC are stable up to ~220â
K. Above this temperature, the intrinsic mobility of the film is high enough that PEQC molecules come into direct contact with the Au(111) surface, which catalyzes the back-conversion. We suggest that this process occurs via a singletâtriplet mechanism induced by electronic coupling between the PEQC molecules and the Au(111) surface
Reactivity of a model SCILL: Influence of co-adsorbed [C2C1Im][OTf] on the dehydrogenation of dimethylamine on Pt(111)
<p>Raw and evaluated data of the IRAS measurements and DFT calculations</p>
Surface Chemistry of a [C<sub>2</sub>C<sub>1</sub>Im][OTf] (Sub)Wetting Layer on Pt(111): A Combined XPS, IRAS, and STM Study
The concept of a solid catalyst with an ionic liquid
layer (SCILL)
is a promising approach to improve the selectivity of noble metal
catalysts in heterogeneous reactions. In order to understand the origins
of this selectivity control, we investigated the growth and thermal
stability of ultrathin 1-ethyl-3-methylimidazolium trifluormethaneÂsulfonate
[C2C1Im][OTf] films on Pt(111) by infrared reflection
absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy
(XPS) in time-resolved and temperature-programmed experiments. We
combined these spectroscopy experiments with scanning tunneling microscopy
(STM) to obtain detailed insights into the orientation and adsorption
geometry of the ions in the first IL layer. Furthermore, we propose
a mechanism for the thermal evolution of [C2C1Im][OTf] on Pt(111). We observe an intact IL layer on the surface
at temperatures below 200 K. Adsorbed [C2C1Im][OTf]
forms islands, which are evenly distributed over the surface. The
[OTf]â anion adsorbs via the SO3 group,
with the molecular axis perpendicular to the surface. Anions and cations
are arranged next to each other, alternating on the Pt(111) surface.
Upon heating to 250 K, we observe changes in geometry and structural
distribution. Whereas at low temperature, the ions are arranged alternately
for electrostatic reasons, this driving force is no longer decisive
at 250 K. Here, a phase separation of two different species is discernible
in STM. We propose that this effect is due to a surface reaction,
which changes the charge of the adsorbates. We assume that the IL
starts to decompose at around 250 K, and thus, pristine IL and decomposition
products coexist on the surface. Also, IRAS and XPS show indication
of IL decomposition. Further heating leads to increased IL decomposition.
The reaction products associated with the anions are volatile and
leave the surface. In contrast, the cation fragments remain on the
surface up to temperatures above 420 K
Au catalyzed energy release in a molecular solar thermal (MOST) system: A combined liquid-phase and surface science study
<p>Raw Data, evaluated files and a list of experiments is provided.</p>