An Azobenzene-Based Liquid Molecular Solar Thermal (MOST) Storage System-Energy Carrier and Solvent.

Area of Science:

• Materials Science
• Chemical Engineering
• Renewable Energy

Background:

• Molecular solar thermal (MOST) systems store solar energy via photoisomerization for later release as heat.
• Liquid azobenzenes (ABs) are explored for MOST applications, but often require specific conditions for efficient operation.

Purpose of the Study:

• Introduce a novel, low-viscosity, green light-active 2,6-difluoroazobenzene for MOST applications.
• Demonstrate its potential as a neat compound and as a MOST-active solvent.

Main Methods:

• Continuous flow synthesis and photoisomerization of 2,6-difluoroazobenzene.
• Characterization of storage densities and photoresponsive properties.
• Exploration as a solvent for electrolytes and other MOST materials (e.g., norbornadiene).

Main Results:

• Achieved high storage densities (218 kJ kg⁻¹ for (Z)-isomer, 137 kJ kg⁻¹ after green light irradiation), surpassing other liquid azobenzenes.
• Demonstrated efficient handling, pumping, and neat-state processing.
• Showcased its utility as a MOST-active solvent, inducing conductivity in electrolytes for electron-catalyzed back-isomerization and co-storing energy with norbornadiene.

Conclusions:

• 2,6-difluoroazobenzene is a highly promising candidate for efficient molecular solar thermal energy storage.
• Its unique properties as a liquid azobenzene and a MOST-active solvent open new avenues for energy storage technologies.