Green hydrogen at the flip of a switch
Single-molecule catalyst produces solar fuel even in the dark

Ulm University

Researchers from Ulm present a new approach for solving one of the biggest challenges of the solar energy transition. They have been successful in developing a system that enables hydrogen to be produced with the power of light at any time of day or year. Future areas of application for this photochemical unit range from demand-based heat production to supplying hydrogen-powered vehicles on demand. The researchers at Ulm University and Jena University present their system, which is based on a single molecule, in the journal “Nature Chemistry”.

Hydrogen (H2) is going to play a key role in the energy transition. At least, this is the ambition of the national hydrogen strategy introduced in 2020. In order to make a substantial contribution toward achieving the goal of climate neutrality, this energy source must be “green” – i.e. produced exclusively with renewable resources. But how can solar hydrogen, for instance, be produced in the evening or the winter based on demand? Chemists in Ulm have found an answer: for the first time, they have succeeded in decoupling sunlight-driven hydrogen production from the course of the day with a molecular photochemical system. The new system even makes it possible to store light energy, so that hydrogen production can be demand-oriented and even start in the dark.

A single molecule can absorb sunlight, store energy and produce hydrogen

Earlier models for hydrogen production were often based on coupling various components such as photovoltaic cells, batteries and electrolysers. However, the energy losses add up at every step with such models, making these methods of hydrogen production not very efficient. The new alternative developed in Ulm, on the other hand, is based on a single molecule that can absorb sunlight, store energy and produce hydrogen. This compact unit makes it possible to separate these steps in terms of both space and time. “With our molecule, light irradiation leads to charge separation and electron storage – the result of which is a liquid fuel that is easy to store. The on-demand production of gaseous hydrogen is achieved by adding a proton source”, explains Professor Carsten Streb from the Institute of Inorganic Chemistry I at Ulm University.

The researchers have tested their system’s performance using a wide range of analytical methods (including catalytic tests and photophysical studies). In these tests, the molecular unit has displayed excellent chemical and photochemical stability. “The modular structure of the system enables chemical changes and an optimisation of the entire system”, explains first author Dr Sebastian Amthor, who completed his PhD at Ulm University and is now conducting research in Spain. In the future, the model will be upscaled and thus serve as a “blueprint” for decentralised energy storage. Possible applications range from climate-friendly electricity and heat production to mobile, solar-powered H2 filling stations for lorries and buses.

Development in the CataLight Transregio Collaborative Research Centre

The photochemical system was developed within the scope of the Transregio Collaborative Research Centre TRR 234 CataLight. In this joint project, researchers from Ulm University and Jena University are taking photosynthesis as a model and developing new materials for energy conversion – one example is artificial chloroplasts for hydrogen production. This project is receiving approximately 10 million euros in funding.

Structural analyses and optical-spectroscopic work describing the catalyst’s response to light, which are relevant for the current publication, were carried out at the Centre for Energy and Environmental Chemistry (CEEC Jena) at Jena University. For these studies, a high-tech device for high-resolution mass spectrometry was used, which was purchased with EU funds within the framework of the regional innovation strategy of the state of Thuringia. “This device made it possible for the first time to determine the structures of the new molecular catalysts in detail”, explains Professor Ulrich S Schubert and Professor Benjamin Dietzek- Ivanšić from Jena.

The Collaborative Research Centre TRR 234 Light-driven Molecular Catalysts in Hierarchically Structured Materials - Synthesis and Mechanistic Studies (CataLight) is funded by the German Research Foundation (Deutsche Forschungsgemeinschaft – DFG).

Sebastian Amthor, Sebastian Knoll, Magdalena Heiland, Linda Zedler, Chunyu Li, Djawed Nauroozi, Willi Tobaschus, Alexander K. Mengele, Montaha Anjass, Ulrich S. Schubert, Benjamin Dietzek, Sven Rau, and Carsten Streb: A single molecule capable of decoupling light- and dark reactions for on-demand solar hydrogen production. Nature Chemistry. DOI: 10.1038/s41557-021-00850-8

Text and mediacontact: Annika Bingmann

Irradiation apparatus
Irradiation apparatus at the Institute of Inorganic Chemistry I: here measurements were carried out for the current publication (Photo: Heiko Grandel)
Functionality of the single molecule catalyst (Diagram: SFB/TRR CataLight)
Functionality of the single molecule catalyst (Diagram: SFB/TRR CataLight)
Prof. Sven Rau and Prof. Carsten Streb, senior authors of the publication
Senior authors of the recently released publication: Prof Sven Rau and Prof Carsten Streb (from left, photos: Eberhardt/Uni Ulm)