Design, testing and characterization of noble-metal catalysts for the heat-release reaction of a molecular solar thermal energy storage isomer pair

Abstract

MOlecular Solar Thermal systems (MOST) are a promising technology to store solar energy in chemical bonds. The heat release from the charged isomers requires an efficient catalysed reaction to deliver its energy on demand. Herein, a series of heterogeneous catalysts featuring varied metal centres and supports was synthesised and evaluated for the thermal back-conversion reaction of one of the most advanced MOST systems, based on the norbornadiene/quadricyclane photoswitch pair. The catalysts were characterised to understand the effects that influence performance. Two key findings were made. Firstly, the best performing catalysts were those where the metal centres were in a metallic state as opposed to being oxidized. Some metals oxidise more readily on alumina than on activated carbon, and therefore, for these metals, the choice of support has a significant effect. Secondly, catalysts with very low loading had disproportionately high activity compared with higher-loading catalysts. This seems to be due to the presence of highly active and highly dispersed particles at low loading, which are much more active than the larger particles that readily form at higher loadings.