Platinum-group-metal nanocatalysts based on carbon aggregates provide a porous structure through which an ionomer network percolates in proton exchange membrane fuel cells. This local structural characteristic is associated with mass-transport resistances and cell performance losses.
EPFL researchers have revealed the nanostructure of platinum catalyst layers for the first time, demonstrating how they could be optimized for fuel cell efficiency.
PEMFCs (proton-exchange membrane fuel cells) are being developed for use in electric vehicles and rely on nanoparticles known as catalysts to initiate electricity-producing reactions between hydrogen and oxygen. Most PEMFC catalysts contain platinum, a rare and valuable metal. As a result, there is a pressing global need to design catalysts that can generate the most electricity while using the least amount of platinum.
Manufacturers combine these catalysts into complex assembled known as catalyst layers. Only now, they had to do it with a clear image of the final structure because traditional imaging procedures nearly invariably resulted in some degree of damage.
Vasiliki Tileli, head of the Laboratory for in-situ nanomaterials characterization with electrons in the School of Engineering, has developed a method to overcome this obstacle by imaging catalysts and their surroundings at temperatures below freezing using cryogenic transmission electron tomography and processing the images with deep learning. They were able to display the nanoscale structure of catalyst layers for the first time.
Tileli said, “We’re still far away from PEMFCs without platinum, which is very expensive. In the short term, we need to reduce platinum loading to make this technology viable for mass production. It’s, therefore, imperative to understand how platinum sits in relation to other materials within the catalyst layer, to increase the surface area contact required for chemical reactions. That’s why it’s quite an achievement to image these catalysts in three dimensions; before, it was impossible to have the right contrast between the different catalyst layer components.”
To improve the surface area contact required for chemical reactions, it is critical to understand how platinum sits with other materials inside the catalyst layer.
It is essential to understand how platinum sits in relation to other materials inside the catalyst layer to optimize the surface area contact necessary for chemical reactions.
Furthermore, the scientists were able to reveal the heterogeneous thickness of a porous polymer layer on the catalysts known as ionomer, which significantly impacts how effectively platinum catalysts work.
This knowledge might be a gold mine for catalyst makers, who could utilize it to create catalysts with more platinum particles coated with the appropriate quantity of ionomer and operate optimally.
The researcher explains, “The ionomer must have a certain thickness for the catalytic reactions to happen efficiently. Because we could do a full reconstruction of catalyst layers with little damage to the structure, we could show, for the first time, how much platinum is covered with an ionomer and the thickness of that coverage.”
The proper amount of ionomer might be used to create catalysts with more platinum particles that work at their best. This information could be a gold mine for catalyst makers.
The cryo-aspect is critical to this research since ionomers, like proteins, are soft and require freezing temperatures to stabilize and protect their structure.
He said. “I think this advanced technique will therefore be useful not just for facilitating the mass manufacturing of PEMFCs through optimized platinum use but also for many different materials science and energy applications, for example, battery storage, water electrolysis, and energy conversion systems in general.”
- Girod, Gasteiger, Tileli,etal . Three-dimensional nanoimaging of fuel cell catalyst layers. Nature Catalysis. DOI: 10.1038/s41929-023-00947-y