Active = dynamic: the secret of copper electrocatalysts
Fuel cells are the focus of modern energy research and are essential for a sustainable energy supply. Whether its heart – the catalyst – works efficiently depends heavily on its material.
The group led by the physical chemist Julia Kunze-Liebhäuser recently succeeded in demonstrating that copper is much better suited as a catalyst than previously thought.
Efficient catalysts convert chemical into electrical energy in a fuel cell. They can also function in electrolysers to split water or to produce synthetic fuels. Finding the right material is often a challenge in the development of catalysts.
“Until now, well-functioning catalysts have often consisted of rare elements such as platinum or iridium, which makes them very cost-intensive,” explains Julia Kunze-Liebhäuser, Professor of Physical Chemistry at the University of Innsbruck.
Scientists are therefore looking for available alternatives. The centuries-old Sabatier principle helps them here. “This principle says that a good catalyst material should not bind the molecules involved in the reaction too strongly or too weakly. The bond should be strong enough to activate the reaction, but also weak enough not to bind the molecules to itself forever and thus bring the reaction to a standstill, ”explains the chemist. “Unfortunately, many materials do not meet this principle, since molecules are either all more strongly or all less strongly bound, while substances are often required that specifically attach certain molecules to their surface more strongly, but others less so.”
In their work published in Nature Catalysis, the team around Julia Kunze-Liebhäuser, in cooperation with Prof. Karsten Reuter from the Fritz Haber Institute Berlin, was able to show that copper has found its own solution to this problem.
In the electro-oxidation reaction of carbon monoxide, the most important intermediate product in the oxidation of fuels in fuel cells, they observed that the surface of a copper catalyst changes during the reaction. “In the literature, copper is described as inactive for this reaction, and our calculations also showed that a copper catalyst should actually not work.
In the experiment, however, we were able to measure a high electrocatalytic activity, ”describes Julia Kunze-Liebhäuser. In order to track down this contradicting result, The scientists took a closer look and found the explanation for the high activity of the copper catalyst with the scanning tunneling microscope. “We found out that copper changes its surface during the reaction and that small islands of a few copper atoms are constantly being formed here. In these protruding, only nanometer-sized clusters, the charge of adsorbing molecules is stored, locally delimited, under the applied voltage, which leads to fundamentally different binding properties to change decoupled, could represent a completely new approach to the fulfillment of the Sabatier principle. With copper, these clusters form spontaneously;
Source: Fritz Haber Institute Berlin/University of Innsbruck