Interview with Carsten Cremers, Manager of the Fuel Cells and Electrolysis Group at Fraunhofer ICT

Q: What it is expected for the work package related to New catalyst supports Fraunhofer ICT is leading?

A: The principle of a catalyst is to reduce the activation energy of a reaction by offering an alternative reaction pathway. For heterogeneous catalysts, as most electro-catalyst including the oxygen evolution catalyst investigated in RECYCALYSE, means that the starting reactant can respond with the surface to form an intermediate that can further react towards the final product. This way, the bind to the catalyst surface is lowered, so the reacted substance can leave the surface it in its original state for the next reaction.

The rate at which this can occur depends on the number of surface sight. Thus, increasing the active surface area is an important tool to raise the activity of a reactor or here an electrode.

Catalyst supports help in achieving this goal by stabilizing very small particles of the actual active ones. This is necessary as nanoparticles like the iridium oxide or iridium ruthenium oxide nanoparticles investigated here tend to be unstable coalescing into larger particles once their diameter is reduced to few nanometres.

Supports are an established tool in the development of heterogeneous catalysts. A special requirement of supports for electro-catalyst is now that they need to be electronically conductive in order not to block the required exchange of electrons at the catalytic active sights.

In fuel cells, high surface area carbon materials are used for this purpose. However, even there the intrinsic instability of carbon at potential exceeding 0.201 V is a known factor limiting the lifetime of fuel cells. For oxygen evolution electrodes operating at potentials between 1.5V and 2.5 V, the use of carbon is not realistic. Alternatives can be found in metal carbides where carbon is stabilised by the binding with a metal, or in certain conductive oxides. Oxides are of particular interest as they may intermittently store oxygen atoms further supporting the reaction.

Q: How is Fraunhofer ICT working on it?

A: In the first months of the project, Fraunhofer ICT has performed extensive literature research on support materials for oxygen evolution catalysts in Proton Exchange Membrane (PEM) water electrolysis. The observation of the acidic conditions encountered in PEM is important as they aggravate possible corrosion issues.

Based on the results, candidate materials could be down-selected. In order to allow for the success of the project in total, it is very important that other partners can follow their work already at an early point. It was therefore decided to select two materials for which commercial availability of a base version is given. In detail, there are antimony doped tin oxides in the first place, and tungsten carbide in second place.

This selection allows our partner Danish Technological Institute (DTI) to start working on the deposition process, while Fraunhofer ICT concentrates on the synthesis and characterization of support batches with improved properties like increased support surface area, further improved corrosion stability, or increased electronic conductivity.

Improved materials obtained at Fraunhofer ICT shall thus be useable with the coating procedures developed at DTI for the general type of support requiring only minor adaptations.