Science + Technology

UCLA, University of Michigan Chemists Report Progress in Quest to Use Hydrogen as Fuel for Cars and Electronic Devices

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Chemists at UCLA and the University of Michiganreport an advance toward the goal of cars that run on hydrogen rather thangasoline. While the U.S. Department of Energy estimates that practical hydrogenfuel will require concentrations of at least 6.5 percent, the chemists haveachieved concentrations of 7.5 percent — nearly three times as much as has beenreported previously — but at a very low temperature (77 degrees Kelvin).

The research, scheduled to be published in late March in theJournal of the American Chemical Society, could lead to a hydrogen fuel thatpowers not only cars, but laptop computers, cellular phones, digital camerasand other electronic devices as well.

"We have a class of materials in which we can change thecomponents nearly at will," said Omar Yaghi, UCLAprofessor of chemistry, who conducted the research with colleagues at the University of Michigan. "There is no other class ofmaterials where one can do that. The exciting discovery we are reporting isthat, using a new material, we have identified a clear path for how to getabove seven percent of the material's weight in hydrogen."

The materials, which Yaghiinvented in the early 1990s, are called metal-organic frameworks (MOFs), pronounced "moffs," whichare like scaffolds made of linked rods — a structure that maximizes the surfacearea. MOFs, which have been described as crystalsponges, have pores, openings on the nanoscale inwhich Yaghi and his colleagues can store gases thatare usually difficult to store and transport. MOFscan be made highly porous to increase their storage capacity; one gram of a MOFhas the surface area of a football field! Yaghi'slaboratory has made more than 500 MOFs, with avariety of properties and structures.

"We have achieved 7.5 percent hydrogen; we want to achievethis percent at ambient temperatures," said Yaghi, amember of the California NanoSystemsInstitute. "We can store significantly more hydrogen with the MOFmaterial than without the MOF."

MOFs can be made from low-costingredients, such as zinc oxide — a common ingredient in sunscreen — and terephthalate, which is found in plastic soda bottles.

"MOFs will have many applications.Molecules can go in and out of them unobstructed. We can make polymers insidethe pores with well-defined and predictable properties. There is no limit towhat structures we can get, and thus no limit to the applications."

In the push to develop hydrogen fuel cells to power cars,cell phones and other devices, one of the biggest challenges has been findingways to store large amounts of hydrogen at the right temperatures andpressures. Yaghi and his colleagues have nowdemonstrated the ability to store large amounts of hydrogen at the rightpressure; in addition, Yaghi has ideas about how tomodify the rod-like components to store hydrogen at ambient temperatures (0–45C).

"A decade ago, people thought methane would be impossible tostore; that problem has been largely solved by our MOF materials. Hydrogen is alittle more challenging than methane, but I am optimistic."

Yaghi, 41, has reason to beoptimistic since only a handful of MOFs have beentested for hydrogen storage thus far. This is not unreasonable given that MOFs are composed of an inorganic component — a metal oxide— and an organic component; he can control their assembly into new structuresnearly at will.

How would hydrogen work in devices like cell phones, laptopcomputers and digital cameras?

"Instead of a battery, one would have a medium such as MOFthat stores hydrogen and releases it into a fuel cell," he said.

Yaghi, whose research overlaps chemistry, materials science andengineering, has long been interested in making materials in a rational way.

"When I started out in chemistry, I always thought it shouldbe possible to take two well‑defined molecules as building blocks andstitch them together into a predetermined chemical structure — almost like youproduce a blueprint of the structure ahead of time and then find the rightbuilding blocks necessary to build it. In this way, one can control thestructure and the composition. This approach was difficult to implement at thebeginning, but is not so difficult at this stage."

Hydrogen, when burned, produces only water, which isharmless to the environment, Yaghi noted. With MOFs, hydrogen is physically absorbed, and it is easy totake the hydrogen out and put it back in without much energy cost, he said.

"The challenge has been, how do youstore enough hydrogen for an automobile to run for 300 to 400 miles withoutrefueling?" Yaghi asked. "You have to concentrate thehydrogen into a small volume without using high pressure of very lowtemperature.

"Our idea was to create a material with pores that attracthydrogen, making it possible to stuff more hydrogen molecules into a smallvolume," he said.

In previous research, Yaghi andcolleagues reported that MOFs also can store largeamounts of methane (natural gas).

"We have materials that exceed the DOE requirements formethane, and we think we can apply the same sort of strategy for hydrogenstorage," he said.

Additionally, Yaghi has shown thatMOFs store prodigious amounts of carbon dioxide atambient conditions, a development relevant to preventing carbon dioxideemissions from power plants and automobile tailpipes from reaching the atmosphere.

The research was funded by the National Science Foundation,the U.S. Department of Energy and BASF (a global chemical company based in Germany).

Co-authors of the present research report, which Yaghi conducted when he was on the faculty at the Universityof Michigan, are Adam Matzger, assistant professor ofchemistry at Michigan, and Antek Wong-Foy, chemistryresearch associate at Michigan.

-UCLA-

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