According to the International Energy Agency (IEA), around 50% of the world’s final energy consumption is used for heating. However, the adoption of solar energy in this area is still quite low compared to fossil fuels. One major issue limiting the broader use of solar energy is its inconsistency in direct availability. A potential solution lies in molecular solar energy storage systems.
Traditional thermal energy storage methods typically save energy over short durations, like keeping hot water. In contrast, molecular solar energy storage systems capture solar energy as chemical bonds, enabling it to be stored for weeks or even months. These specialized molecules, known as photoswitches, can absorb solar energy and later release it as heat when needed. A significant challenge with existing photoswitches is the balance between how much energy they can store and how efficiently they can absorb solar light, which impacts overall performance. Researchers from Johannes Gutenberg University Mainz (JGU) and the University of Siegen are addressing this issue through innovative collaboration.
Separating the absorption and storage processes of solar energy
This new category of photoswitches was first developed by Professor Heiko Ihmels’s team at the University of Siegen, showcasing impressive energy storage capabilities that rival those of conventional lithium-ion batteries. Initially, their performance was restricted to activation by UV light, which only covers a small segment of the solar spectrum. The collaborative teams from Mainz and Siegen have now introduced a method for indirect light harvesting, similar to how the light-harvesting complex operates in photosynthesis. This strategy involves adding a second component, known as a sensitizer, which has excellent ability to absorb visible light. “In this method, the sensitizer absorbs light and then transfers that energy to the photoswitch, which isn’t directly excited by this light,” explained Professor Christoph Kerzig from JGU’s Department of Chemistry.
This new approach has improved the efficiency of solar energy storage by over tenfold, marking a significant advancement for the energy conversion research community. These systems could potentially be applied in everything from home heating solutions to large-scale energy storage, paving the way for more sustainable energy practices.
Studying mechanisms is crucial for discovering and optimizing reactions
The research team from Mainz, led by Professor Christoph Kerzig and PhD student Till Zähringer, performed comprehensive spectroscopic analyses to delve into this intricate system, crucial for uncovering the mechanisms at play. Each stage of the reaction was meticulously scrutinized by the paper’s first author, Till Zähringer, leading to a solid understanding of the system’s functionality. “This allowed us to not only significantly enhance the light-harvesting capacity but also to boost the efficiency of converting light into stored chemical energy,” Zähringer explained. Under practical conditions, each photon absorbed can initiate a process of forming chemical bonds, a phenomenon that is infrequently seen in photochemical reactions due to multiple pathways where energy can be lost. The researchers validated the system’s durability and practicality by cycling between energy storage and release states multiple times using solar light, demonstrating its potential for real-world use.
The findings have been published in Angewandte Chemie, where the work has received recognition as a Hot Paper due to outstanding evaluations from scientific peers.
This research project was financially supported by the German Research Foundation (DFG) and the German Federal Environment Foundation, which provided a project grant to Christoph Kerzig and a fellowship to Till Zähringer, respectively. Additional backing came from the House of Young Talents and the Stiftung Nagelschneider at the University of Siegen.
