As projections indicate a dramatic increase of our renewable energy usage of up to 50 % from 2019 to 2040, a number of challenges have to be met in order to achieve sustainable energy systems that are less dependent on the conventional ones.

ICMAB Researcher Kasper Moth-Poulsen will be approaching some of these challenges within the context of the ERC awarded project PHOTHERM “Photo Thermal Management Materials” through the use of particular kinds of molecular photoisomers, molecules whose chemical properties could be used to develop molecular solar thermal (MOST) systems.

A review of this line of research, introducing the concept, criteria and state-of-the-art of MOST systems has now been published in the journal JOULE under the title “Storing energy with molecular photoisomers”, and Prof. Kasper Moth-Poulsen is one of its authors.

The MOST basics

Isomers are molecules that can have more than one arrangement of its atoms without changing its molecular formula. Photoisomers can be excited via exposure to light into a different arrangement, and some can retain a metastable high-energy state, which could make them useful to store energy:

“The system can’t be directly compared to other energy storage systems. The same material is both capturing solar energy, and storing it, it is a “2-in-1 system” which may bring about new opportunities for integration into future thermal management devices.” Says Prof. Kasper Moth-Poulsen.

The photoisomer can then be restored through a thermal or catalytic process, reverting it to its original stage and releasing the stored energy as heat. This could help match the fluctuations in supply and demand in energy that solar power can struggle to respond to.

“Even though the basic idea of solar energy storage in molecular photoisomers dates back more than 100 years, the concept is still at an early development stage.”

MOST challenges

MOST Systems will have to face a few challenges before they are ready to enter our lives.

• Solar spectrum match - modify the molecules to extend their absorption wavelength spectrum
• Extension of the energy storage time - modify the molecules to ensure the storage of energy for a reasonable period (at least 6-10 hours)
• Increasing energy density - develop low-molecular-weight molecules to increase their energy density
• Alternative strategies to improve overall performance - study the molecules in real conditions to see the effect of the different factors that can influence their performance
• Controlling energy release - control when and how the stored energy is released: study thermal activation, optical activation, electrocatalytic, and catalytic activation.
• Cycling properties -  long-term stability, including the absence of side reactions, is necessary for use as a rechargeable energy storage system

All these variables are currently being researched in order to accelerate the approach of this technology. The MOST project is a European Project that aims to develop and demonstrate a zero-emission solar energy storage system based on molecular solar thermal systems. This project aims to develop liquid systems from TRL ≈ 2 to ≈ 4.

At the same time, companies like the startup Solartes are also developing these systems in composite materials for e.g. thermally regulating windows.

And now, Kasper Moth-Poulsen and his research team will follow this research at ICMAB: “we will try to work with these systems in new ways, by coupling the photochemical transformations to phase change and by that developing new ways of regulating the temperature.”

Reference Article:

Storing energy with molecular photoisomers
Zhihang Wang, Paul Erhart, Tao Li, Zhao-Yang Zhang, Diego Sampedro, Zhiyu Hu, Hermann A. Wegner, Olaf Brummel, Jörg Libuda, Mogens Brøndsted Nielsen. Kasper Moth-Poulsen
Joule, 2021. DOI: 10.1016/j.joule.2021.11.001

Published in Open Access