US scientists have designed from first principles nanoparticles that efficiently oxidise carbon monoxide (CO) - a contaminant commonly found in hydrogen used to run fuel cells. 

A major problem facing fuel cells is that the hydrogen-rich materials feeding the reaction often contain CO, which is formed during hydrogen production. This CO 'poisons' the electrodes in the fuel-cell devices, deteriorating their efficiency. 

Now, a team led by Bryan Eichhorn of the University of Maryland and Manos Mavrikakis of the University of Wisconsin, Madison, have desinged and made a catalyst for the preferential oxidation (PROX) of CO comprising a ruthenium (Ru) core inside a Platinum (Pt) shell. 

Graphical representation of alloy, core-shell and linked monometallic nanoparticles. Pt is black and Ru is red © Nature

The team found H₂ streams cleaned by their nanoparticles spontaneously combust at 30°C whereas temperatures of 85-170°C are required after using other Pt- and Ru-based catalysts. That suggests less of the contaminating CO was present in the H₂ after selective oxidation by the new nanoparticles.

The researchers say the enhanced activity of the new catalyst is due to the availability of more CO-free Pt sites on the nanoparticles' surface and a new hydrogen-mediated reaction that oxidizes CO at room temperature through the formation of a hydroperoxy intermediate. 

Over the long term, the researchers hope to make new electrocatalysts that will replace current anode and cathode materials in fuel cells. 'The combination of precise nanosynthesis techniques with state-of-the-art electronic structure theory opens the door to the prediction and production of new materials, which are much more potent catalysts for a number of chemical processes,' Eichhorn says.

While core-shell nanoparticles are not new in catalysis, the controlled synthesis of such catalysts based on calculations and experiments is, says electrochemist Nicolas Alonso-Vante of the University of Poitiers. 'This work shows that very fundamental aspects obtained for model extended surfaces can be applied to real-world materials, such as nanocatalysts, thus bridging the gap between surface science and catalysis,' he says. 

Kira Welter

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