OPTIMAS measurement method provides new insights into water-splitting photocatalysts

Because of its high energy density, hydrogen is an excellent energy storage. It is not without reason that cars operated with fuel cells are regarded as a serious alternative to environmentally friendly battery vehicles. Although the only by-product of the fuel cell installed in the car is water, in today's most important method of hydrogen production, which is the steam reforming of natural gas, large amounts of greenhouse gases are generated. An environmentally friendly alternative is photocatalytic water splitting. However, this method has to be greatly improved for large scale application. In the renowned journal "Angewandte Chemie", researchers from Ulm, Munich and Kaiserslautern provide an efficient method for the characterization of water-splitting catalysts:

Pump-Probe Fragmentation Action Spectroscopy: A Powerful Tool to Unravel Light-Induced Processes in Molecular Photocatalysts
D. Imanbaew, J. Lang, M. F. Gelin, S. Kaufhold, M. G. Pfeffer, S. Rau, C. Riehn
Angew. Chem. Int. Ed. 2017, doi: 10.1002/anie.201612302

An interdisciplinary group led by Professor Sven Rau at the University of Ulm is researching the environmentally friendly production of hydrogen by photocatalysis. In artificial photosynthesis, water is separated into its constituents hydrogen and oxygen using solar energy: a special metal complex - in the presented model consisting of ruthenium - serves as a light trap. The ruthenium then generates a free electron which travels to the reaction center of platinum or palladium. Hydrogen is then produced at this center. However, existing photocatalysts are not active enough for extensive industrial use.

At the TU Kaiserslautern the water-clearing photocatalysts were characterized using mass spectrometry by the group around Christoph Riehn of the Department of Chemistry. Based on the investigated model photocatalysts, the scientists could show that the properties known from solution also apply to the gas phase. For this purpose, they have compared data obtained over the last decade with the current results. In addition, there was evidence of rapid jumping of electrons from the photochemical energy collector, in this case a ruthenium complex, to the catalytic reaction center, a platinum complex. Thus, the research group was able to demonstrate the functionality of the new method by detailed studies on model catalysts. They gained insight into the photochemical elementary processes of these catalysts by clearly assigning the steps in the energy or electron transfer process. The research groups were supported by Dr. Maxim F. Gelin (TU Munich), who contributed important simulations to the interpretation of the experimental data.

The Kaiserslautern measurement method, which combines mass spectrometry with femtosecond laser spectroscopy, was developed within the collaborative research center SFB/TRR 88 (Collaborative effects in homo- and heterometallic complexes, 3MET). The team of Christoph Riehn is part of the group of Professor Niedner-Schatteburg (Department of Chemistry and Research Center OPTIMAS, TU Kaiserslautern).