# Harnessing Both Phase Change and Isomerization: High-Energy-Density Azobenzene-Composites for Efficient Solar Energy Storage

## TL;DR

A new material combines phase change and isomerization to store solar energy more efficiently with higher energy density.

## Contribution

A novel azobenzene composite is designed to enhance solar energy storage by leveraging both phase change and isomerization.

## Key findings

- C14Azo-MA retains the isomerization properties of C14Azo while enhancing energy storage.
- The composite achieves a 14.42% higher energy density than pure myristic acid.
- Supercooling is enabled through molecular photoisomerization and intermolecular interactions.

## Abstract

Organic phase change materials (OPCMs) show immense application potential in solar energy storages owing to high energy storage capacity and latent heat efficiency. However, it is difficult to achieve prolonged energy storage due to the sensitivity of phase change to environmental temperature, and adding other substances will lead to a decrease in total energy density. Herein, azobenzene organic phase change composite (C14Azo-MA) was designed and prepared by doping myristic acid (MA) with an azobenzene derivative (C14Azo) featuring a carbon chain identical to that of the MA matrix. C14Azo-MA was systematically characterized by UV–Visible absorption spectroscopy and differential scanning calorimetry. The results showed that the C14Azo-MA retains the same isomerization properties as the C14Azo dopant. C14Azo-MA, due to its molecular photoisomerization and enhanced intermolecular interactions, establishes a new energy barrier and forms supercooling within C14Azo-MA, thereby allowing the storage of thermal energy below the crystallization temperature of MA. Notably, the C14Azo-MA exhibits a high energy density of 225.08 J g−1, surpassing that of pure MA by 14.42%. This work holds significant potential for solar energy storage applications.