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A molecular solar thermal (MOST) storage system is based on the capture of solar energy through photoisomerization, which is later released as thermal energy. In this study, a low-viscosity, green-light-active compound, 2,6-difluoroazobenzene, is introduced, which can be efficiently irradiated, pumped, and handled in its neat state. The synthesis and isomerization processes are conveniently performed in a continuous flow setup. Storage densities of 218 kJ kg⁻¹ for the 100% (Z)-isomer (137 kJ kg⁻¹ after green light irradiation) have been achieved, representing the highest values reported for liquid azobenzenes (ABs). The ability to undergo green light irradiation and to be processed in the neat state positions this compound as a strong candidate for energy storage applications. Additionally, the liquid AB has been employed as a MOST-active solvent. For instance, the solvation of an electrolyte has been shown to induce measurable conductivity, enabling complete electron-catalyzed back-isomerization. Alternatively, it has been used as a solvent for a higher-energy MOST material. As a proof-of-concept, a norbornadiene (NBD) was dissolved in the AB solvent, allowing the energy of both the NBD and the AB to be utilized. Further optimization of the solute–solvent systems is required to fully exploit the potential of this new concept for efficient energy storage.
- Schatz, D
- Averdunk, C
- Fritzius, R
- Wegner, HA
- Institute of Organic Chemistry, Justus Liebig University Giessen, Heinrich-Buff-Ring 17, 35392, Gießen, Germany
