New design concept produces new fuel cell catalyst

An international team of scientists has developed a concept for designing catalysts that elegantly correlates their geometric and adsorption properties. They validated their approach by designing a new platinum-based catalyst for hydrogen-powered fuel cells.

Such fuel cells generate electricity by oxidizing hydrogen at a cathode, forming water, while oxygen is reduced at an anode. The oxygen reduction reaction requires a platinum-based catalyst, but platinum (Pt) is extremely expensive and the world's annual output would not be sufficient for the widespread adoption of fuel cells in electric cars.

It is well known, however, that only a few particularly exposed areas of the platinum-based catalyst are catalytically active: these areas are known as active centers. A team of scientists from the Technical University of Munich and the Ruhr University Bochum (Germany), the Ecole Normale Superieure (ENS) de Lyon, Centre National de la Recherche Scientifique (CNRS), Universite Claude Bernard Lyon 1 (France) and Leiden University (Netherlands) have now determined what makes a good active center.

A common method used in developing catalysts and in modeling the processes that take place on their surfaces is computer simulation. But as the number of atoms increases, the required quantum chemical calculations quickly become extremely complex.

By developing a new methodology called ‘coordination-activity plots’, the research team came up with an alternative solution that elegantly correlates a catalyst’s geometric and adsorption properties. As they report in Science, this methodology is based on the ‘generalized coordination number’ (GCN). This is a variant of the coordination number, which is the number of atoms surrounding a specific atom, and involves weighting each surrounding atom according to its own coordination number.

Calculated with the new approach, a typical Pt (111) surface has a GCN value of 7.5. According to the coordination-activity plot, the optimal catalyst should, however, have a value of 8.3, which could potentially be obtained by inducing atomic-size cavities into the platinum surface.

In order to validate the accuracy of their new methodology, the researchers computationally designed a new type of platinum catalyst for fuel cell applications, which they then prepared experimentally using three different synthesis methods. In all three cases, the resultant catalyst showed up to three and a half times greater catalytic activity.

"This work opens up an entirely new way for catalyst development: the design of materials based on geometric rationales which are more insightful than their energetic equivalents," says Federico Calle-Vallejo from Leiden University. "Another advantage of the method is that it is based clearly on one of the basic principles of chemistry: coordination numbers. This significantly facilitates the experimental implementation of computational designs."

"With this knowledge, we might be able to develop nanoparticles that contain significantly less platinum or even include other catalytically active metals," says Aliaksandr Bandarenka, tenure track professor at Technical University of Munich. "And in future we might be able to extend our method to other catalysts and processes, as well."

This story is adapted from material from the Technical University of Munich, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.