Spectroscopic and Mechanistic Understanding of MOF-based Photocatalysts for Solar Fuels Generation.

• Applicants: Professor Dr. Roland A. Fischer; Professor Dr. Jürgen Hauer
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Inorganic Molecular Chemistry - Synthesis and Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 547756633

The project will advance the understanding of the electron transfer processes in structured materials. We will be harnessing the chemistry of coordination space of MOFs for assembling photosensitizers and metal complex catalysts and for in-depth investigations of the resulting photoelectrochemical nanoreactors. We already established a MOF-based colloidal model system, enabling the hydrogen evolution reaction (HER) and the CO2 reduction reaction (CO2RR), producing syngas, i.e., a valuable mixture of CO and H2, from H2O and CO2 in the presence of a sacrificial electron donor. Our project envisions addressing issues associated with the loss of excited- and reduced-states, (i) by investigating the energy and electron transfer kinetics, and the reaction electron transfer cascade mechanism and (ii) by optimizing the molecular design of our model system for CO2 reduction to CO. To study photoinduced mechanisms, one would usually resort to time-resolved methods such as transient absorption. For the MOF colloids, however, such experimental designs suffer from diffuse light scattering and settling of the MOF particles. We will overcome these limitations by both chemical and spectroscopic means. We will downscale the MOF particles below 200 nm and stabilizing them with surfactants to reduce scattering. Crucially, a twofold spectroscopic advancement will be concomitantly pursued: (1) Scatter contributions will be minimized by employing rapid scan transient absorption spectroscopy at 100 kHz repetition rate, leading to faster data acquisition time and improved signal-to-noise ratio. (2) Scatter contributions will be completely avoided by ultrafast spectroscopy based on photocurrent-detection using samples of MOF-particles mounted on electrically conductive transparent metal oxide substrates. A state-of-the-art testing photoreactor will be developed for improving transient spectroscopic methods and effective performance screening. The device will allow for an automated and high-throughput IR-spectroscopic product and photochemical yield determination after exposure of the MOF-sample to a well-defined light dose delivered by a high-power LED. We will combine spectroscopic knowledge, photocatalytic performance with chemical structure by the development of molecular Re catalysts for CO2 reduction to integrate in our light harvesting MOF hosts in various ways. We envision tailoring anchoring groups as well as spacer length and rigidity toward a series of fine-tuned light-harvester assemblies within the pores of a structured framework. Thus, the impact of key parameters such as orientation, distance, and nature of interaction can be unveiled at a (supra)molecular level.

• DFG Programme: Research Grants
• Major Instrumentation: Fourier Transform Infrared Spectrometer
• Instrumentation Group: 1830 Fourier-Transform-IR-Spektrometer