Fuel cells require platinum as a catalyst, because platinum plays a central role in the oxygen-reduction reaction on the electrodes. Unfortunately, it is rare and extremely expensive. It is therefore important to use as little of it as possible in order to be able to offer fuel cells at an economically reasonable price.
How small can a cluster of platinum atoms become in order to be highly catalytically active? This was the question asked by a research team at TU Munich led by Roland Fischer, Professor of Inorganic and Organometallic Chemistry, Aliaksandr Bandarenka, Professor of Physics of Energy Conversion and Storage, and Alessio Gagliardi, Professor of Simulation of Nanosystems for Energy Conversion.
To answer the question, they modelled the entire system on the computer. "It turned out that there could be certain optimal platinum cluster sizes," explains Roland Fischer. Particles that are approximately 1 nm in size and contain around 40 platinum atoms are ideal. "Platinum catalysts of this size have a small volume, but a large number of strongly active sites, which leads to high mass activity," says Bandarenka.
Interdisciplinary cooperation at the Centre for Catalysis Research (CRC) has played an important role in the researchers' success. Theoretical skills in modelling, joint discussions as well as physical and chemical knowledge from experiments ultimately lead to a model of how catalysts can ideally be designed in terms of the shape, size and size distribution of the components involved.
The CRC also has the know-how to manufacture and experimentally test the calculated platinum nanocatalysts. "There is a lot of inorganic synthesis art behind this," says Kathrin Kratzl, one of the three first authors of the study along with Batyr Garlyyev and Marlon Rück.
Our catalyst is twice as good as the best commercially available catalyst," says Garlyyev. This is not yet sufficient for commercial applications. A 50 percent reduction in the amount of platinum is already impressive, but a further 80 percent reduction is necessary to bring fuel cells into cars in large numbers, for example. Not even primarily because of the price, but because platinum is not available in such large quantities.
In addition to spherical nanoparticles, the researchers hope that far more complex forms will lead to higher catalytic activity. The computational models that have now been established are ideal for such models. "However, more complex forms require even more complex synthesis methods," said Bandarenka. Joint computational and experimental studies will become increasingly important in the future.