"We need a thorough shake-up of our global energy industry"

16 December 2022

Professor Carsten Streb and his team at the Department of Chemistry of Johannes Gutenberg University Mainz (JGU) have developed a molecule that is capable of storing solar energy and releasing it whenever required. Their pioneering work represents a possible solution to the worldwide energy crisis.

"At present, gasoline seems to be the answer to everything," Professor Carsten Streb points out. And there is a good reason for this. "There is no other material that makes energy available so efficiently. It is stored in every single molecule of gasoline." Of course, we are currently striving to find alternatives. However, so far these have not proved to work nearly as efficiently.

"Take a battery that is coupled with a solar cell, for example. First of all you need various components for the battery itself – a metal jacket, cabling, electrodes. All these are essentially inactive elements as they don't actually store energy themselves and simply provide the configuration that makes this possible. A solar cell is able to capture some 20 percent of the solar energy it is exposed to. Well and good, the battery can store nearly 100 percent of that. However, if we decide we want to transfer this energy to a flexible carrier system so that we can transport and use it in much the same way as gasoline, we will end up losing a large proportion of that energy." And what about hydrogen? "In principle, it is very much like gasoline. Unfortunately, the yield we get when we use electrolysis to produce hydrogen is only roughly 40 percent. If we take all the factors into account, at present it looks like that, on balance, we can achieve an efficiency of just 5 percent."

Two dye molecules, one energy storage system

Streb picks up a 3D model from his desk. "It was our aim to create a single molecule able to harvest solar energy, store it, and readily release it again when needed." He is holding a small, bright blue plastic structure. "Of course, you can't handle molecules just like that because they are so tiny you can't even see them. However, a model like this allows me to make chemistry quite literally a hands-on discipline. And this is our new molecule." It consists of just three elements: two dye molecules that are linked together in the middle by an energy storage unit.

As Streb explains, he could now place a glass flask filled with countless numbers of these molecules on his window sill. As it stores the solar energy from light, the slightly orange-colored liquid would turn bright blue. With the help of a simple acid it would then be possible to release the stored energy in the form of green hydrogen. The color of the liquid would then fade and it would return to its original state, ready for the next energy harvesting/release cycle. "At present, we are able to achieve an efficiency of some 45 percent. And there is a major advantage over gasoline in that we have is a closed loop system. In other words, this system is sustainable."

Streb was appointed Professor of Inorganic Chemistry at Mainz University in April 2022. He had previously undertaken research into aspects of energy conversion and storage at the Helmholtz Institute Ulm and Ulm University. Working within the Transregional Collaborative Research Center CataLight, short for Light-driven Molecular Catalysts in Hierarchically Structured Materials – Synthesis and Mechanistic Studies, in which the Mainz-based Max Planck Institute for Polymer Research is also participating, he and his interdisciplinary team developed innovative materials that can be used for purposes that are not necessarily energy-related, such as the purification of drinking water, for example.

"My main topic is sustainability," he says. "Together with my team, I strive to make a contribution that will help us master the current global challenges. While others glue themselves to roads in order to draw attention to climate change, we prefer taking a path less dramatic but all the more productive."

Ideal research environment at JGU

Streb decided to come to Mainz University because there was already a strong focus on his particular interests here in the Department of Chemistry. "Sustainability, energy supply, and the related resources are considered core issues of our time. Many of my colleagues are undertaking research in the corresponding fields. That suits me and my research perfectly. Moreover, the discipline of chemistry at JGU underwent major restructuring two years ago. All fields of chemical research were brought together in one department, there are no longer various institutes. We are communicating extensively with each other and the range of equipment and facilities that has become available as a result is outstanding. I'm really impressed by what has been done."

Interdisciplinary research and education are important for Streb. "If you want to study chemistry, you will also need to be well versed in aspects of physics and mathematics. Much of the subject matter students have to deal with in their first semester is related to physics because they need to know what an atom looks like if they are going to go on to construct a molecule. And if you want to know how a molecule reacts with its environment, well, then you have to turn to biology. No discipline is an isolated island. What we as teachers try to impress on our students is the existence of this interrelation between fields and disciplines." Streb applies the same philosophy to his research. He is always making connections. "I have been involved in exploratory discussions and I now see definite links between our materials and what is of major relevance in physics and the research being done in the PRISMA+ Cluster of Excellence, for example."

The Gutenberg Research College (GRC) of Mainz University also welcomed Professor Streb as a new fellow. "This means that I have access to the resources necessary to set up a new lab here in Mainz. The coronavirus pandemic has taught us how to take different approaches to what we do and how to work in unconventional places. I have learned from this. We will design rooms and areas that are particularly flexible and can be adapted to the needs of the moment."

Research has produced a functioning concept

It is the task of the GRC to promote cutting-edge research at JGU. So Streb, the holder of a number of awards for his research, is in exactly the right place here. A few months ago, he unveiled his solar energy gathering molecule at the Falling Walls Conference in Berlin. This is attended by researchers from around the world who give presentations on their pioneering breakthroughs. The jury for Engineering and Technology selected Streb as a Global Call Winner.

He opened his presentation at the conference with a striking message: "In one single hour the sun provides more energy to Earth than mankind consumes within a whole year." Thus, making use of this natural sunlight, we can overcome the global energy crisis. The new molecule provides one way of doing so. "However, we are still facing certain challenges. The dye we use is rather expensive and is decomposed by exposure to the sun after a while. But we have demonstrated what is possible. And as researchers, I think that is exactly what we are supposed to do – provide concepts for things that will work. At the same time, we are training others who will be able to take these concepts a step further."

There is one thing that Streb is quite sure about: "We need a thorough shake-up of our global energy industry." He and his team have made a start by providing an important component for this. And they intend to continue with their efforts beyond disciplines and institutions.