High Energy Density in Azobenzene-based Materials for Photo-Thermal Batteries via Controlled Polymer Architecture and Polymer-Solvent Interactions

Seung Pyo Jeong,Connor J Boyle,Edward Harder,Wolfgang Damm,Dhandapani Venkataraman,Lawrence A Renna,Hyunwook S Kwak

doi:10.1038/s41598-017-17906-w

Seung Pyo Jeong, Connor J Boyle + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-17906-w

Copy DOI

Abstract

Energy densities of ~510 J/g (max: 698 J/g) have been achieved in azobenzene-based syndiotactic-rich poly(methacrylate) polymers. The processing solvent and polymer-solvent interactions are important to achieve morphologically optimal structures for high-energy density materials. This work shows that morphological changes of solid-state syndiotactic polymers, driven by different solvent processings play an important role in controlling the activation energy of Z-E isomerization as well as the shape of the DSC exotherm. Thus, this study shows the crucial role of processing solvents and thin film structure in achieving higher energy densities.

Highlights

In organic PTBs, light converts a stable isomer into a high-energy meta-stable isomer
Computational studies by Kolpak et al predict that azobenzene units placed 4.24 Å apart on a rigid scaffold, such as carbon nanotubes (CNTs), can lead to dramatic increases in energy storage densities—from ~200 J/g for unassembled azobenzene units to 820 J/g for azobenzene molecules assembled on CNTs1
Thermogravimetric analysis (TGA) of these polymers (Supplementary Fig. S20) showed no mass loss until 200 °C, which indicated that the polymers are thermally stable in the temperature range of 0 °C–140 °C for differential scanning calorimetry (DSC) studies to evaluate the energy density

Summary

Introduction

In organic PTBs, light converts a stable isomer into a high-energy meta-stable isomer (charging). The meta-stable isomer can be converted back to the low-energy isomer on-demand (discharging)[6,7,8], where the excess energy (energy difference: ∆H) is typically released as heat Since this configurational isomerization does not generate by-products, the charging-discharging cycle can be repeated without loss of active material. We hypothesized that we can achieve high energy densities by (a) anchoring azobenzene on polymer backbones to achieve high functional group density in a polymer chain, (b) placing end-groups on the polymers that can self-assemble into cylindrical structures, similar to CNTs, and (c) tuning polymer-polymer interaction by choosing different processing solvents. In PMA, the distance between two syn ester groups in a syndiotactic triad is calculated to be ~5 Å, similar to distance between azobenzene units on CNTs. We chose hexabenzocoronene (HBC) as our end-group because it can self-assemble through π-π stacking interactions into cylindrical structures[17,18]. We tested two reference solvents with low boiling point and high solubility for the polymer, dichloromethane (DCM) and tetrahydrofuran (THF), to understand role of polymer-solvent interaction and optimal structure for high energy density

Methods

Results

Conclusion