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Understanding Solid-State Photochemical Energy Storage in Polymers with Azobenzene Side Groups
Callum Wallace1, Kieran Griffiths1, Benjamin L Dale1
1Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom.
ACS Applied Materials & Interfaces
|June 23, 2023
Summary
Solar thermal fuel polymers store energy using light-induced structural changes. Adding an alkyl linker to azobenzene side groups significantly boosts energy storage and efficiency in these advanced materials.
Area of Science:
- Materials Science
- Polymer Chemistry
- Photochemistry
Background:
- Solar thermal fuel (STF) materials store energy via light-induced structural changes in photoactive molecules, releasing heat upon reconversion.
- Solid-state STF devices face challenges due to limited molecular mobility in condensed phases.
- Polymers offer a promising platform for solid-state STF by balancing bulk properties with molecular-level mobility.
Purpose of the Study:
- To systematically investigate methacrylate- and acrylate-based polymers with azobenzene side groups for STF applications.
- To elucidate the mechanism of energy storage and release in these polymer systems.
- To determine the factors influencing energy density and reconversion kinetics.
Main Methods:
- Synthesis and characterization of polymers with azobenzene side groups, both directly attached and with alkyl linkers.
- Photoisomerization studies to assess switching efficiency and isomeric state conversion.
- Thermal analysis to determine glass transition temperature and reconversion kinetics.
- Gravimetric energy density measurements.
Main Results:
- Polymers with directly attached azobenzene groups showed properties consistent with previous studies.
- Incorporating an alkyl linker between the azobenzene and polymer backbone significantly enhanced photoswitching efficiency, approaching quantitative conversion to the Z-isomer.
- The alkyl linker reduced the glass transition temperature and accelerated thermal reconversion, yet solid-state half-lives exceeded 4 days.
- A maximum gravimetric energy density of 143 J g⁻¹ was achieved, a 44% increase over polymers with directly attached azobenzene.
Conclusions:
- Alkyl linkers are crucial for optimizing azobenzene-based polymer STFs, enhancing energy storage capacity and photoswitching efficiency.
- These modified polymers demonstrate potential for applications requiring daily energy storage and release cycles.
- The study establishes a clear link between polymer structure, particularly the presence of alkyl linkers, and improved energy storage performance.
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