Engineers devise a way to make cleaner, cheaper energy
Researchers at Tufts have discovered a way to make hydrogen from fossil fuels using far less platinum or gold than current fuel processing technology requires. Their research demonstrates that 90 percent of precious metals used today may be removed from the catalyst without affecting its ability to produce hydrogen.
The finding could mean a potential cost savings of millions of dollars in the materials required to commercialize the fuel cell technology.
The research was first published in the July 3 edition of "Science Express," the online version of the journal Science, which also published the work later in the summer.
A fuel cell consists of two electrodes sandwiched around an electrolyte. Hydrogen fed to the one electrode (anode) passes through the electrolyte in the form of protons and combines with oxygen on the other electrode (cathode), making water and producing heat. Electricity is generated in the process. A fuel cell will produce energy in the form of electricity and heat as long as fuel and oxygen are supplied. To produce fuel-cell quality hydrogen, an important step involves the removal of any by-product carbon monoxide, which poisons the fuel cell anode catalyst.
"A lot of people have spent a lot of time studying the properties of gold and platinum nanoparticles that are used to catalyze the reaction of carbon monoxide with water to make hydrogen and carbon dioxide," said Maria Flytzani-Stephanopoulos, professor of chemical and biological engineering at Tufts and the lead researcher on the project. "We find that for this reaction over a cerium oxide catalyst carrying the gold or platinum, metal nanoparticles are not important. Only a tiny amount of the precious metal in nonmetallic form is needed to create the active catalyst. Our finding will help researchers find a cost-effective way to produce clean energy from fuel cells in the near future."
She and her two colleagues, doctoral student Qi Fu and research professor Howard Saltsburg, were funded with a $300,000, three-year grant from the National Science Foundation. They have filed a provisional patent for their research. Their cutting-edge work in catalytic fuel processing to generate hydrogen for fuel cell applications is one of the major undertakings at Tufts' Science and Technology Center.
The researchers' article is based on the "water-gas shift" reaction they use to make hydrogen from water and carbon monoxide over cerium oxide loaded with gold or platinum. Typically, a loading of 1-10 weight percent of gold or other precious metals is used to make an effective catalyst. But the Tufts team discovered that after stripping the gold with a cyanide solution, the catalyst was just as active with a slight amount of the gold remaining—one-tenth the normal amount used.
"This finding is significant because it shows that metallic nanoparticles are mere 'spectator species' for some reactions, such as the water-gas shift," Flytzani-Stephanopoulos said. "The phenomenon may be more general, since we show that it also holds for platinum and may also hold true for other metals and metal oxide supports, such as titanium and iron oxide."
Flytzani-Stephanopoulos said the research "opens the way for new catalyst designs so more hydrogen can be produced using less precious metal."
Fuel cells currently are being used on a trial basis in some buses, cars and even hotels, but they're expensive. It may take up to 10 years until the technology is used in transportation and by the general population. (Since the 1960s, one type of fuel cell has powered NASA spacecraft.)
"We've raised the issue of now having to look back and see if less precious metal may be used in other similar applications," said Saltsburg. There's much more to be done, and that's what makes the research exciting."