In what could be a breakthrough on the road to a pollution-free hydrogen economy, researchers say they have developed a “crystal sponge” material that can store nearly three times more hydrogen than any other known substance.
Obstacles to mass market vehicles that some day run on hydrogen include storage capacity. Test cars that use hydrogen in fuel cells to create an electric propulsion system now get just 150 miles or so on a tank the same size as those in gasoline cars, which can travel 300 or 400 miles on a tank.
Chemists at UCLA and the University of Michigan claim their material is the first to achieve the kind of storage capacities required to make hydrogen fuel practical. They are publishing their findings in late March in the Journal of the American Chemical Society.
The material was developed by UCLA chemist Omar Yaghi, who described it as just one in a large class of compounds he invented in the early 1990s.
MOFs at work
The compounds are known as as metal-organic frameworks, or MOFs. A press release from the National Science Foundation, which helped fund the research, said the compounds “have a crystal structure that resembles a scaffold made of linked rods — a structure that gives them a multitude of nanoscale pores, and a correspondingly huge internal surface area where gas molecules can attach.”
What’s more, only minute amounts of MOFs are needed. “A pinch of a MOF,” the NSF added, “has roughly the surface area of a football field.”
And MOFs can be made inexpensively from chemicals like zinc oxide, a common ingredient in sunscreen, and terephthalate, which is found in plastic soda bottles.
Yaghi said the structures can be tailored easily, and that his lab has made more than 500 different MOFs in recent years.
“We have a class of materials in which we can change the components nearly at will,” he said in the press release. “There is no other class of materials where one can do that.”
‘No limit to the applications’
The material might also be applicable to laptop computers, cell phones, digital cameras and other electronic devices.
“MOFs will have many applications,” Yaghi said. “Molecules can go in and out of them unobstructed. We can make polymers inside the pores with well-defined and predictable properties. There is no limit to what structures we can get, and thus no limit to the applications.”
But the material is not quite ready for market: The high storage densities are so far possible only at -321 degrees Fahrenheit. Yaghi said he was optimistic that is only temporary given that so many MOF variations are possible and have yet to be tested.
No commercial plans have been announced but two other research funders are major players: the U.S. Department of Energy and chemical giant BASF.
Other obstacles to vehicles powered by hydrogen, which emits no pollutants, include the costs of extracting hydrogen from other compounds, the lack of a fueling infrastructure and the costs of fuel cell stacks, which are coming down but are still much more expensive than internal combustion engines.
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