UniSysCat Colloquium

Dr. Robert Seidel

Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Start Time: Wednesday, October 23, 2024 05:15 pm

End Time: Wednesday, October 23, 2024 06:30 pm

or via Zoom
C 264

Resonant soft X-ray photoelectron spectroscopy studies of liquids and solid-liquid interfaces

Dr. Robert Seidel

Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

I will present recent research topics my group and I have been working on at the HelmholtzZentrum Berlin, where we spectroscopically investigate the electronic structure of liquids and solid–liquid interfaces; in particular, metal-oxide nanoparticle–water interfaces using liquid microjets, and electrolyte–anode interfaces using micro-fluidic (photo-)electrochemical cells.

A lot of effort is being made to finding abundant, catalytically active and stable (photo)electrocatalysts, with transition metal oxides being a promising material class. The issues of efficiency and stability are due to related electronic-structure processes driving the oxygen evolution reaction and hydrogen evolution reaction at the solid-liquid interface between the electrocatalyst and the electrolyte. I will present our spectroscopic results on several transition metal oxide nanoparticles dissolved in water, which mimicked the interface of relevant (photo)electrocatalysts for water splitting in their true environment by using soft-X-ray synchrotron photoemission spectroscopy in combination with the liquid microjet technique. Most pressing questions regarding the molecular-level understanding of such buried interfaces are how ions adsorb at the solid–solution interface, how interfacial ions are solvated, how the solvent molecules respond, and how all this affects charge-state and energy transfer across the interface.

I will then give a short overview of our (valence) ambient-pressure photoelectron and Augerelectron spectroscopy studies on solid (photo)electrocatalysts (either as thin film or as supported nanoparticles), on which a thin film of liquid water has been deposited. The important questions that we wanted to answer are whether the catalytic processes affect only the chemical nature of the electrode surface, or do they also induce chemical (phase) changes in the bulk material. What is the molecular and electronic structure of the catalyst when a voltage is applied? How is the molecular-orbital interplay between the oxygen and the transition metal in the catalyst? And what is the effect of electrolyte on the electronic structure during the oxygen evolution reaction?

I will also present an introduction to my recently applied ERC Consolidator grant, which was granted in January 2024 and started in September this year. The project is called WATER-X and deals with the soft X-ray spectroscopic investigations of the early-time processes in photocatalytic water-splitting at the metal-oxide nanoparticle–water interface using the liquidjet technique. The novelty here is the use of resonant time-resolved soft X-ray photoelectron spectroscopy, whereby a combination of UV/Vis pump and tunable soft X-ray probe laser pulses from a powerful 500 W, 53 kHz high-harmonic laser source (up to 600 eV photon energy) will be used to investigate transient species at the metal-oxide nanoparticle surface in a bulk water environment.

I will conclude my talk with two examples of how normal Auger-electron and resonant Augerelectron spectroscopy can be used to study the solvation shell composition and the hydrogenbonding network between solutes and the water solvent molecules in aqueous solutions.

Prof. Dr. Roel van de Krol

Organizer

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