A jury-rigged inkjet printer has helped chemists discover the most efficient catalyst yet at converting methanol to electricity in fuel cells--devices that are being hotly pursued by companies worldwide as a clean alternative to combustion engines. The new catalyst is described in today's Science.
Current fuel cell catalysts break down methanol into carbon dioxide, protons, and electrons: The electrons are routed through a wire to power a car or do other work, eventually arriving at another electrode where they meet up with the mobile protons. But these platinum-ruthenium catalysts waste about 25% of the energy stored in the fuel as heat. The search for an improved combination of metals has concentrated on various mixtures of two metals, or occasionally three. Few research groups have tried to sort through the dizzying array of combinations of four or more metals.
To speed up the search, chemist Tom Mallouk and his Pennsylvania State University, University Park, colleagues took a hacksaw to a commercial inkjet printer and modified the machine to spray droplets of different metal salts instead of ink. A computer controlled the spraying, creating an array of dots with various metal-salt combinations, which were then reacted all at once to form active catalysts. To pick out the best performers, the researchers simply treated their array with a compound called nickel PTP, which fluoresces a faint blue in the presence of protons. A small voltage across the array lit up the catalysts. Colleagues at the Illinois Institute of Technology in Chicago, who made electrodes from the material and incorporated them into working fuel cells, found that the best catalyst contained iridium and osmium in addition to the standard metals. It was 40% more efficient at generating electricity than a straight platinum-ruthenium mix under simulated real-world conditions.
This improvement may not be enough to justify commercial fuel cells using iridium and osmium, which cost more than platinum, says Tom Fuller of International Fuel Cells in South Windsor, Connecticut. But he adds that the promising results of this first attempt suggest that the brute force approach at creating catalysts "is definitely worth pursuing."