Scientists working on automotive fuel cells have come up with a way to turn a molecular contaminant into a power source. Others say the advance may help open the door to using renewable energy resources.
Low-temperature fuel cells use platinum catalysts to extract electricity from hydrogen gas. But if the gas is produced from fossil fuels--the most common source--it invariably contains carbon monoxide (CO), which poisons the catalysts. Makers of low-temperature fuel cells--called polymer electrolyte membrane (PEM) fuel cells--must send the fuel through an initial chamber heated to 500°C or more. At this high temperature, CO molecules react with water molecules to make carbon dioxide (CO2), which is vented away. The process cleans up fuel effectively. But it's costly and inefficient to heat the chamber and then cool the exhaust gases, as most low-temperature fuel cells require.
Earlier this year, a team led by James Dumesic of the University of Wisconsin, Madison, found a cool alternative: a membrane coated with gold nanotubes and nanoparticles. On the nanoscale, Dumesic explains, normally unreactive gold becomes so active that it catalyzes reactions swiftly even at low temperatures. Now Dumesic's team has used their nanogold catalyst to react CO and liquid water to create CO2, hydrogen ions (H+), and electrons (e–). Instead of letting the energy in the electrons fizzle away, they captured it with electron-ferrying "redox" compounds known as polyoxometalates (POMs) dissolved in the water surrounding the membrane.
To recover the energy from the electron-toting POMs, Dumesic's team piped the solution, mingled with hydrogen ions from the CO reaction, to the front end of a PEM fuel cell. There, a positively charged electrode stripped off the electrons and turned them into usable current. The oxidized POMs were then recycled to the gold-nanotube reactor to convert more CO. The rest of the process was standard fuel-cell chemistry.
"It's pretty novel and interesting," says Matthew Neurock, a catalysis expert at the University of Virginia, Charlottesville. Neurock and others say the work might help make fuel cells cheaper. That could be welcome news for those who advocate generating hydrogen fuel from renewable fuels such as agricultural waste, Neurock says, because producing hydrogen from "biomass" also produces large amounts of CO.