The fuel of the future could be hydrogen—if it can be made cheaply enough. Currently, electrolyzers (machines that split water into its constituent hydrogen and oxygen) need a catalyst, namely platinum, to run; ditto fuel cells to recombine that hydrogen with oxygen, which produces electricity. The problem is that the precious metal costs about $1,700 to $2,000 per ounce, which means that hydrogen would be an uneconomical fuel source unless a less costly catalyst can be found. But researchers from the Massachusetts Institute of Technology (M.I.T.) and Monash University in Australia report in Science today that they may have a cost-effective solution.
Chemist Daniel Nocera, head of the M.I.T.'s Solar Revolution Project, focused on one side of the equation: splitting water into its constituent hydrogen and oxygen molecules. This can be done well, but it remains difficult to actually separate the molecules. But Nocera and postdoctoral fellow Matthew Kanan discovered it could be accomplished by simply adding the metals cobalt and phosphate to water and running a current through it. In contrast to platinum, cobalt and phosphate cost roughly $2.25 an ounce and $.05 an ounce, respectively.
"We [have] figured out a way just using a glass of water at room temperature, under atmospheric pressure," Nocera says. "This thing [a thin film of cobalt and phosphate on an electrode] just churns away making [oxygen] from water."
Inspiration for the new catalyst came from nature; Nocera studied the chain of processes that take place during photosynthesis, such as how plants use the energy from sunlight to rearrange water's chemical bonds. In a future hydrogen economy, he imagines, a house would function much like a leaf does, using the sun to power household electricity and to break down water into fuel—a sort of artificial photosynthesis.
According to John Turner, a research fellow at the National Renewable Energy Laboratory in Golden, Colo., who was not involved in the research, the discovery could reduce the need for platinum in a conventional electrolyzer. He believes it could also play a role in a future large-scale hydrogen generator, which would collect the energy from sunlight in huge fields and then run that electric current through water to produce vast amounts of hydrogen to meet, for example, the demand from a future fleet of hydrogen-powered vehicles. "That's what his advance is pointing towards," he says, "finding an alternative catalyst that will allow us to do oxygen evolution (breaking the bonds of water or H2O and forming oxygen) in concert with hydrogen" on a grand scale.
But that still leaves plenty of platinum in the other side of the equation: the fuel cells that combine hydrogen and oxygen back into water to harvest electricity. Chemist Bjorn Winther-Jensen of Monash University in Australia and his colleagues addressed that problem by developing new electrodes for fuel cells made from a special conducting polymer, that costs around $57 per counce.
During experiments, the polymer proved just as effective as platinum at harvesting electricity—and the work could prove immediately relevant in mini fuel cells, such as the kind that are being designed for computers.
In order for this to work on the grand scale of a fuel cell stack for a hydrogen vehicle or power plant "we need to develop a more three-dimensional structure to get thicker electrodes and a higher current per square centimeter," says Winther-Jensen. Regardless, by reducing or eliminating platinum, the two studies help pave the way for a future hydrogen economy.