Unveiling the Potential of Heterogeneous Catalysts for Molecular Solar Thermal Systems

Abstract

Solar energy utilization has gained considerable attention due to its abundance and renewability. However, its intermittent nature presents a challenge in harnessing its full potential. The development of energy storing compounds capable of capturing and releasing solar energy on demand has emerged as a potential solution. These compounds undergo a photochemical transformation that results in a high‐energy metastable photoisomer, which stores solar energy in the form of chemical bonds and can release it as heat when required. Such systems are referred to as MOlecular Solar Thermal (MOST)‐systems. Although the photoisomerization of MOST systems has been vastly studied, its back‐conversion, particularly using heterogeneous catalysts, is still underexplored and the development of effective catalysts for releasing stored energy is crucial. Herein we compare the performance of 27 heterogeneous catalysts releasing the stored energy in an efficient Norbornadiene/Quadricyclane (NBD/QC) MOST system. We report the first benchmarking of heterogeneous catalysts for a MOST system using a robust comparison method of the catalysts’ activity and monitoring the conversion using UV‐Visible (UV‐Vis) spectroscopy. Our findings provide insights into the development of effective catalysts for MOST systems. We anticipate that our assay will reveal the necessity of further investigation on heterogeneous catalysis.

State-of-the-art and challenges towards a Molecular Solar Thermal (MOST) energy storage device

“…This makes the system capable of absorbing photons from the solar spectrum beyond 400 nm. 12 A long list of NBD derivatives have been prepared and tested for this application. 33,34…”

“…However, recent efforts in this regard have been made to expand the understanding of this catalytic process to achieve real implementation in a device. 12…”

“…). 12 This method allows quick and robust assessment of the efficiency of a large series of heterogeneous catalysts using UV-VIS spectroscopy as the analytical method to rapidly characterize the NBD/QC ratio. Using minimal amounts of QC (10 mg) solution and catalyst (1 mg), the evaluation of the efficiency over time is quantified by the amount of NBD generated in the back-conversion reaction (Fig.…”

“…In MOlecular Solar Thermal (MOST) systems, 11 a parent molecule is photoconverted upon light excitation into a high-energy metastable isomer, which can release the energy stored on demand in the form of heat. 12,13 The simplicity of this technology relies on being a closed system where no reagents are consumed and no by-products are formed, thus implying a much cleaner solution for solar energy storage. Although having some promising features, this technology is not free from drawbacks.…”