Au‐Catalyzed Energy Release in a Molecular Solar Thermal (MOST) System: A Combined Liquid‐Phase and Surface Science Study

Abstract

Molecular solar thermals (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 Au(111) 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 the catalytically triggered energy release. In the liquid phase, we did not observe any decomposition of the photoswitch, no deactivation of the catalyst within 100 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 110 K. Multilayers of PEQC are stable up to ~220 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 singlet‐triplet mechanism induced by electronic coupling between the PEQC molecules and the Au(111) surface.

The Norbornadiene/Quadricyclane Pair as Molecular Solar Thermal Energy Storage System: Surface Science Investigations

“…Since Au(111) acted as highly active catalyst material for the conversion of QC7 (see below), the molecule pair NBD5 / QC5 was also characterized on a gold surface in a combined synchrotron radiation photoelectron spectroscopy (SRPES) and IRRAS study under UHV conditions, along with PEC‐IRRAS in the liquid phase [113] . Indeed, the high catalytic activity of gold was also confirmed for QC5 , as the contact with the catalyst led to the instantaneous cycloreversion reaction to NBD5 , even at cryogenic temperatures of ~110 K; specifically, no spectroscopic differences were detectable upon adsorption of submonolayers of NBD5 and QC5 .…”