How Adsorption Affects the Energy Release in an Azothiophene-Based Molecular Solar-Thermal System

Molecular solar-thermal (MOST) systems combine solar energy conversion, storage, and release within one single molecule. To release the energy, different approaches are applicable, e.g., the electrochemical and the catalytic pathways. While the electrochemical pathway requires catalytically inert electrode materials, the catalytic pathway requires active and selective catalysts. In this work, we studied the catalytic activity and selectivity of graphite(0001), Pt(111), and Au(111) surfaces for the energy release from the MOST system 3-cyanophenylazothiophene along with its adsorption properties. In our study, we combine in situ photochemical IR spectroscopy and density functional theory (DFT). Graphite(0001) is catalytically inactive, shows the weakest reactant-surface interaction, and therefore is ideally suitable for electrochemical triggering. On Pt(111), we observe strong reactant-surface interactions along with moderate catalytic activity and partial decomposition, which limit the applicability of this material. On Au(111), we observe high catalytic activity and high selectivity (>99%). We assign these catalytic properties to the moderate reactant surface interaction, which prevents decomposition but facilitates energy release via a singlet-triplet mechanism.