One of the biggest problems facing solar energy is storage. We highlighted this issue in the pros and cons of solar energy. Since the Earth receives more energy from the sun than humans are able to use at one time, more energy is absorbed through energy facilities than is used. At the moment, however, it is difficult to store solar energy so that it can not only be used during sunny days but during nighttime, cloudy weather, and high peak times as well. This caused researchers at Linköping University in Sweden to research storing solar energy in a new molecule.
Since the research began, the researchers have developed a molecule that absorbs and stores energy from the sunlight in chemical bonds. Bo Durbeej, leader of the study, explained that the molecule can take two forms: a parent form that absorbs energy from the sun and an alternative form that stores the energy, creating a potential long-term use for solar energy storage. The alternative form stores energy because it changes the structure of the parent form so that it is energy-rich and stable.
The molecule developed is a “molecular photoswitch.” Molecular photoswitches always come in two forms that differ in chemical structure. This allows the forms to have different properties. In the case of the molecule for solar energy storage, the difference is energy content. The structure of the molecular photoswitches is influenced by light energy, meaning that the structure and properties can be changed when exposed to light.
According to the researchers’ words, the study, which was published in the Journal of the American Chemical Society, found, “Overall, we conclude that photoinduced changes in aromaticity facilitate the electrocyclization of dithienylbenzene switches.”
Photoswitches can have other potential uses as well. Notably, it is predicted that photoswitches can be used in molecular electronics, where the two forms of the molecule have different electrical conductivities. Similarly, photoswitches may also be used in photopharmacology, where one form is pharmacologically active, allowing it to bind to a specific protein, and the other form is inactive.
In many researches, experiments are conducted before theoretical research confirms the findings of the experiment. For this newly developed molecule, though, theoretical work was conducted before actual experiments. The reason for this is that Durbeej and his team are theoretical chemists and conduct calculations of chemical reactions. This includes advanced computer simulations that are performed on supercomputers in the National Supercomputer Centre, NSC, in Linköping.
The calculations on these supercomputers showed that the developed molecule would perform as desired, meaning that it would be both stable and energy-rich enough to store solar energy. The supercomputer also found that it could happen very quickly. More specifically, it showed that it could happen in 200 femtoseconds. Scientists at the Research Centre for Natural Sciences in Hungary then built the molecule and performed experiments. Their experiments confirmed the theoretical predictions about the molecule.
In order for the molecule to store large amounts of solar energy, the researchers have tried to make the energy difference between the two molecule forms as large as possible. The parent form is “aromatic,” meaning that it is highly stable. The reason for this is that the basic molecule has three aromatic rings. Whenever light is absorbed, though, the molecule becomes less stable, or loses aromaticity, as it becomes more energy-rich. From their study, they have shown that switching between aromatic and non-aromatic, or stable and non-stable, states can potentially be a major benefit in the field of molecular photoswitches.
In the study, the authors explain, “… there is a loss of aromaticity during the initial photoexcitation that produces a reactive, antiaromatic excited state.”
Durbeej explains that most chemical reactions start when the molecule has high-energy and passes to one with low energy. In the newly developed molecule, however, Durbeej and his team did the opposite. They started with a low energy molecule and turned it into one with high energy. Although researchers expected the process to be difficult, they found that the reaction can occur both quickly and efficiently.
Now, the researchers have to examine the most efficient way for the stored energy to be released from the molecule in order to better use solar energy for commercial use.
Related: Tesla Solar Roof