Monolayer of Platinum Atoms on a Tungsten Carbide Support Catalyzes the Electrolytic Production of H2 Effectively and Cheaply; Significant Reduction in Platinum Loading

Electrolysis of water, powered by wind or sun energy, offers a zero-carbon pathway for the production of hydrogen. While platinum is a very active and commonly used catalyst for the hydrogen evolution reaction (HER), its high price (around US$52/g earlier this year) and limited world-wide supply make its use a barrier to the mass-production of hydrogen via water electrolysis.

Jingguang G. Chen and a team at the University of Delaware have introduced a new method for reducing the use of platinum in electrolysis catalysts without losing efficiency: the layering of an atomic layer, or monolayer (ML), of platinum on low-cost tungsten monocarbide (WC) substrates. A paper on their work was published online 30 Sep in the journal Angewandte Chemie International Edition.

When the ML Pt catalysts are compared to 5–10 nm Pt nanoparticles used in state-of-the-art PEM electrolyzers, it is seen that an order of magnitude
reduction in platinum loading may be achieved.

—Esposito et al.

Current attempts to reduce the use of costly platinum in catalysts by depositing platinum particles onto a support have not been efficient enough. The platinum atoms often settle too far inside the porous support and are shielded from the reaction.

Chen said that his team’s aim was to deposit a single layer of platinum atoms onto an inexpensive planar support so that all the platinum atoms can participate in the reaction.
However, if such a monolayer of metal atoms is deposited onto a support, the atoms interact with the substrate. The electronic structure of the atoms can change because the distances between the individual atoms in the layer can be different from those in the pure metal. In addition, bonding between the platinum and atoms of the support can lead to undesired effects. This can greatly disrupt the catalytic properties.

Chen and his team selected tungsten carbide as a carrier. This inexpensive material has properties very similar to those of platinum. They deposited thin films of tungsten carbide onto a tungsten substrate and added platinum atoms by vapor deposition. The chemical and electronic properties of these atomic platinum monolayers on tungsten carbide did not differ significantly from those of a block of pure platinum. The catalytic efficiency of the supported platinum monolayer is also correspondingly strong.

These ML Pt-WC catalysts represent a significant decrease in platinum loading and associated platinum cost compared to that currently used in many electrolysis
applications. Further work is needed to develop high-surface area ML Pt-WC structures for high-current-density applications and to investigate the long-term stability of this type of
promising HER catalyst. Finally, considering the electrochemical stability of WC, the ML Pt-WC systems should be promising materials to replace bulk platinum in other
electrochemical and photoelectrochemical applications

—Jingguang G. Chen

Resources

• Daniel V. Esposito, Sean T. Hunt, Alan L. Stottlemyer, Kevin D. Dobson, Brian E. McCandless, Robert W. Birkmire, and Jingguang G. Chen (2010) Low-Cost Hydrogen-Evolution Catalysts Based on Monolayer Platinum on Tungsten Monocarbide Substrates. Angewandte Chemie International Edition, doi: 10.1002/anie.201004718

Tags: gray spheres, hydrogen evolution, tungsten carbide

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