Hydrogen Dynamics

The focus is  on development of spectroscopic techniques that allow one to gain insight into the interplay between electronic, optical, magnetic and chemical properties of matter and hydrides. The current areas of expertise include, but are not limited to, table-top ambient pressure XPS for studying metallic and organic membranes exposed to hydrogen and other gasses,  and magneto-optical Faraday and Kerr effect set-up for analysis of photo- and electrochemically induced electronic structures of water splitting catalysts.



Chemical analysis of CO2 reduction

A range of special analysis tools are utilized to characterize processes generating fuel from CO2 and hydrogen. We make use of our state-of-the-art facilities establishing collaborations and proving consulting for academia and industry. The element in focus is hydrogen as its analysis faces specific challenges. Here, we collaborate with a number of large research facilities (PSI-SINQ, RAL-ISIS, ORNL-SNS) providing neutrons as a selective probe for hydrogen in matter.

Recent highlights are the development and utilization of neutron imaging to observe the CO2 reduction in real-time in collaboration with the Laboratory for Neutron Scattering and Imaging at PSI. The movie below shows the diffusion of water into mm-sized zeolite beads. Further fascinating results are found in the recent publication in Journal Physical Chemistry.

The video shows a H2O absorption experiments into mm-sized zeolite beads, visualized using neutron imaging. Image size is 4x5 mm2, time step is 1 frame per minute (fpm).

Inelastic neutron scattering evidence for anomalous H–H distances in metal hydrides

Hydrogen in metals alters the electronic structure of such materials and hence modifies the physical and chemical properties. In conventional transition metal hydrides containing atomic hydrogen, the minimum hydrogen–hydrogen distances are around 2.1 Å under ambient conditions (Switendick criterion). Although hints of H–H distances below 2.1 Å in AB2 alloys have been reported, evidence is inconclusive as hydrogen positions are difficult to locate by diffraction techniques. Here, inelastic neutron scattering is used as a local probe of the hydrogen interactions together with electronic structure modeling of a well-studied and prototypical metal hydride ZrV2Hx. The results provide evidence for anomalous hydrogen–hydrogen distances as short as 1.6 Å. The findings provide insights leading to the creation of materials with properties such as very high Tc superconductivity and other quantum behaviors.

LightCheC project in collaboration with the University of Zurich

“Laser membrane photoemission and magneto-optical spectroscopy shining light on solar water splitting” (see also https://www.empa.ch/web/s502/catalytic-methanation) We are heading for a comprehensive understanding of the electronic structure and its dynamics of materials for solar water splitting. The work may be divided into two parts: the investigation of homo-geneous and heterogeneous solar water splitting by time resolved magneto-optical spectroscopy (trMOKE) and by laser-induces photoemission. For the latter, we are developing a pulsed laser-driven plasma UV source and membrane-based tabletop photoemission set-up. Thus, the method provides information on in-situ probing of the electronic changes in the catalyst over the course of the reaction and offers an alternative to the expensive and often inaccessible synchrotron sources. The magnetic properties of materials are very sensitive to the electronic properties and thus serve as a probe for the changes induced by light and adjacent chemical processes in photocatalytic reactions. Thus, we take advantage of the trMOKE approach for studying magnetic and optical properties of homogeneous and heterogeneous systems in transmission and reflection geometries. Apart from empirical investigations, we model the obtained data using the established models for anticipating the activity of catalytic sur-faces (e.g., the Norskov model). We are aiming at extending these models by the time dimension as needed in photo-catalysis.