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Electrochemical interfaces for energy conversion

Dr. Chris Baeumer (https://people.utwente.nl/c.baeumer)

Challenge: store intermittent renewable energy

To meet the challenges of climate change and energy and resource efficiency, it is necessary for renewable energy sources to replace current fossil fuel based technologies as soon as possible. This is a significant challenge because of the intermittency of most renewable energy sources.

Green hydrogen for energy storage

Therefore, energy transformation and storage options such as conversion to chemical fuel are necessary. The simplest and most attractive candidate for climate-neutral fuel is the production of hydrogen through power-to-gas approaches. Excess electricity from renewable energy can be used to split water into hydrogen and oxygen gas, and the energy stored in the hydrogen gas can be used later on or in a different process, effectively storing energy and coupling different sectors. 

Designing efficient catalysts

For this water-splitting reaction, catalyst materials are required, which reduce the amount of energy needed to generate a given amount of gas. These materials must be made of earth-abundant and safe materials, and must be efficient at catalysing the reaction to increase efficiency and stable under reaction conditions. Despite more than 200 years of research, the exact reaction pathways are not yet understood, and it is still unknown how the catalyst surface properties change during the reaction. We approach this fundamental research question through a materials-by-design approach and through novel characterization tools. 

Atomically-defined thin film catalysts

We utilize atomically defined surfaces of epitaxial catalyst thin films. This class of materials allows selective tuning of the stoichiometry, crystallographic orientation, strain state and surface termination of the catalysts. Thus, we can study the effects of the chemical, crystallographic, electronic, and magnetic structure of the catalysts. In addition, we can stimulate new properties by combining different materials on a nanometre-length scale. The figure on the side shows examples of the different nano processes that can occur and that we can investigate and exploit with these materials. See link for details. The structure-property-function relationships that we identify and the new materials we create will help us identify design rules for future catalysts that are efficient and stable.

Characterization during the reaction (“operando” science)

When we apply a voltage to electrodes immersed in an electrolyte (e.g., our catalyst materials during water electrolysis), multiple reactions occur simultaneously: While we begin to split water into oxygen and hydrogen, the surface of the catalyst changes the chemical composition, the structure and the electronic properties as well, especially at the catalyst surface. Some details are described here. All of these properties determine if the material can be a good catalyst. Therefore, we need to understand and engineer the true active state of the catalyst surface during the reaction.

We achieve this understanding using new characterization tools that can probe the catalyst surface during the water splitting reaction, including X-ray spectroscopy. These experiments are performed at the MESA+ Institute at the University of Twente and at international synchrotron facilities. The available techniques are summarised here.