Mathematisch-Naturwissenschaftliche Fakultät

Institut für Mathematik

Fachgebiet: Physikalische und Theoretische Chemie/ Katalyse

Betreuer: Prof. Dr. Ralf Ludwig

Dipl. Chem. Steffen Fischer
(e-mail: )

Mechanistic Understanding and Improvement of Photochemical Proton Reduction Catalyzed by Iron Carbonyl Complexes for Sustainable Hydrogen Production

This work addresses the investigation of the mechanism of three homogeneous, photochemical proton reduction systems for hydrogen production catalyzed by iron carbonyl complexes. For this purpose, operando IR spectroscopy coupled with gas volumetry was applied together with XAS and NMR spectroscopy as well as ESI-MS, cyclic voltammetry, and quantum chemical computations. The first two systems make use of an iridium-based photosensitizer, while in the third system, a copper-based photosensitizer is applied.

For the first system, the catalytically active species and resting state of the system as well as the rate determining step and deactivation mechanisms could be identified.

In the second system, additionally phosphines are applied as co-catalysts. Notably, in this case, a self-assembling [FeFe]-hydrogenase active site mimic could be detected as catalytic key complex that improves the stability and performance of the system. The requirements on the phosphine substituents and the reaction conditions for the formation of such a complex were determined. Application of the pre-synthesized complex was found to increase the initial hydrogen production rate. The reason for a decreased performance in case of application of excessive amounts of phosphine as co-catalyst was elucidated.

In the third system, the same [FeFe]-complex was observed although it dispenses with phosphine as co-catalyst. The phosphide ligand that is necessary for the formation of the complex was found to originate from the diphosphine ligand dissociated from the photosensitizer. The latter was confirmed to be in equilibrium with an inactive copper species.

The findings of this work were the basis of a fully in-situ self-assembling copper/iron-based proton reduction system developed by the Beller group. This proves that application of spectroscopic and other analytical methods and mechanistic investigations contribute substantially to the understanding and improvement of catalytic systems.