New CNT catalyst uses 100 times less platinum

ENGINEERS at Aalto University, Finland, have developed an electrocatalyst for hydrogen production which uses 100 times less platinum than conventional electrocatalysts, yet with similar efficiency.

Electrolysers, which use electricity to split water and make hydrogen, are expected to be an important way to make use of, and therefore store, excess electricity from renewables and help to balance demand and consumption. However, today’s catalysts rely on prohibitively-expensive volumes of platinum which restricts uptake. In addition, the EU lists platinum as a critical raw material and is trying to reduce its use. Chemical engineering professor Tanja Kallio and physical chemistry professor Kari Laasonen, say their electrocatalyst could provide an solution.

The electrocatalyst is based on carbon nanotubes (CNTs). The researchers use an electrodeposition process to coat the surface of the CNTs with platinum atoms. Kallio says that the platinum deposits in particles consisting of just a couple of atoms. On other surfaces, such as graphene, the particles are larger.

“We believe this is because the carbon atoms of the curved surface are in a strained state, which makes them prone to stabilising platinum on the surface of the nanotube. This ensures that the platinum atoms form small and catalytically active particles. Our modelling showed that the more strained the carbon bonds are, the better the stabilisation of the platinum,” said Kallio.

These small particles mean that more active sites are exposed, making the catalyst more efficient. The researchers found that the diameter of the CNTs is important. Smaller CNTs are more curved, increasing the strain of the atoms, and thus stabilising the platinum particles more effectively.

In tests in a laboratory electrolyser, the CNT-based electrocatalyst had similar activity to commercial platinum electrocatalysts.

“In small-scale conditions and at room temperature, the electrocatalyst is stable and usable for a long time. The next step is to increase the scale of production and test the functionality of the electrocatalyst in practical applications, which are often carried out at a higher temperature,” says Kallio.

ACS Catalysis doi.org/b4rw