Originally published in Sandia Lab News

November 1, 2002

Performance of new material termed ‘astonishing’; research on it is expanding

By Nancy Garcia

KARL GROSS (standing) and Eric Majzoub (seated) are developing a promising new class of hydrides for hydrogen storage .(Photo by Bud Pelletier)

In creating promising materials to store hydrogen, Sandia researchers have pushed theoretical limits, invented a better method of synthesis, and attracted attention from scientists, research partners, and automotive companies along the way.

This month, the research is expanding under two new Laboratory Directed Research and Development grants to further fundamental understanding of the promising materials and to demonstrate integration with a fuel cell. The newly funded work comes on the heels of a wellreceived invited plenary talk at an international meeting last month in Alsace, France.

Meanwhile, the new synthesis method is subject to a pending patent, and four industry leaders from automotive and oil companies have inquired about possible partnerships. Material made with the new low-cost, direct synthesis method has no hydrocarbon impurities that could damage a fuel cell and operates 10 to 20 times more quickly to charge or discharge hydrogen.

Materials researcher Karl Gross (8723) has cycle-tested the new material, sodium alanate hydride, up to 160 times and terms its performance “astonishing.” With Eric Majzoub (8723), he is studying it as a model system for developing future hydrogen storage systems. “We have been working very hard on developing optimized versions of this material,” Karl says.

More than three years of work have been invested in studying the fundamental and engineering properties of these materials with the goal of developing a practical means to store hydrogen for hydrogen-powered cars.

“Given the progress we’ve had,” Karl says, “I think we'll get there.”

Hydrogen’s advantages over fossil fuels include its lack of polluting emissions and the fact that it can be produced anywhere from renewable energy resources such as solar electricity or biomass. Proponents of an energy economy that emphasizes hydrogen point to the potential to improve urban air quality, decrease greenhouse gases (released by burning fossil fuels) that contribute to global warming, and gain independence from foreign oil.

Already, points out Karl, demonstration applications exist to generate power in a distributed system (off the electric “grid”) with hydrogen fuel, to run portable electronic devices on hydrogen, and to operate vehicles using hydrogen combustion engines and also hydrogen fuel cells. (Fuel cells convert chemical energy to electrical energy, creating water and heat without emitting hydrocarbon pollutants or “greenhouse gases.”)

Storing gaseous hydrogen does pose challenges, however. “It doesn't matter what your power plant is,” comments Karl, “the biggest problem is storage.”

The FreedomCAR initiative announced by Energy Secretary Spencer Abraham in January seeks to promote the use of hydrogen as a primary fuel. It targets a vehicle system’s initial hydrogen storage at about 6 to 8 weight percent hydrogen. Given the tradeoffs between weight and volume, that goal accommodates roughly a 300-mile driving range per fill-up.

“No material provides that yet,” says Analytical Materials Science Dept. 8723 Manager Jim Wang. “Our research for the past few years has been on the leading edge of hydride development,” however, and has identified the class of material that appears to come the closest to that goal.

The material Karl and Eric are investigating was first shown in 1996 by German scientists to have achieved the breakthrough of being able to absorb and release hydrogen at reasonable pressures and temperatures when the material was doped with titanium. The ability of such hydrides to release hydrogen was known for half a century, but earlier versions of the material were not easily reversible.

Their model sodium alanate hydride has a theoretical reversible capacity of 5.6 weight percent hydrogen. This is more than double commercial room-temperature hydrides, which store about 2 weight percent hydrogen, and is equal or better than high-pressure or liquid hydrogen storage methods. Experimenting with material synthesis, they found that milling the elemental components together directly rather than relying on the common solvent synthesis process, was not only a more simple and less costly method, it also improved the purity and performance of the material. Steady improvements have been made in the materials, increasing the deliverable hydrogen from 2.8 to currently over 4.3 weight percent hydrogen.

‘A whole new world of materials’

Each of these alanates outperformed about 15 other inexpensive hydrides that operate at close to room temperature. Karl hopes Eric’s work to understand fundamental properties of alanates will suggest new types of complex hydrides. “If it does work,” he says, “that opens up a whole new world of materials.”

Hydride storage of hydrogen fuel competes with pressurized storage (at 5,000 psi) and is an alternative to storage of liquid hydrogen, at 25 degrees above absolute zero, in a fiber-wrapped tank.

The new, more-quickly charging material increases the appeal of hydrides, Karl points out. “Nobody wants to wait 20 or 30 minutes to fuel up, unless you put gas stations next to a Starbucks — so you can get your hydrocarbons one way or another,” he jokes.

A classic hydride may be thought of as a “sponge” in which the hydrogen is absorbed into the metal and fills spaces in the crystal lattice of the material. Karl and Eric note that when being charged with hydrogen, the alanates actually incorporate hydrogen in a two-step chemical reaction that forms lightweight hydrogen-metal complexes (that have covalent bonding character). The desorption process involves the chemical decomposition of the hydrides again in a two-step process. About two-thirds of the hydrogen is released in the first decomposition reaction and the remaining hydrogen is released in the second decomposition step. These thermal decomposition processes will deliver hydrogen at over an atmosphere of pressure above about 110 degrees C. This is near the temperature of a fuel cell's waste heat, which can be used to warm the hydride bed to speed release of the remaining hydrogen.

A breakthrough invention? Perhaps

For that reason, “this is really an ideal application,” Karl says.

The Sandia hydride researchers kicked off an alanate working group meeting for DOE, which has funded the work to date at Sandia. The working group includes United Technologies, the University of Hawaii, Savannah River, and the Florida Solar Energy Center. Eric and Karl also work with the National Institute of Standards and Technology (NIST), the Colorado School of Mines, the University of Geneva, and the International Energy Agency on aspects of the hydride research.

Within DOE, Karl says, Sandia is “probably one of the leading labs for the FreedomCAR program.” Adds 8000 VP Mim John, “We may just have a breakthrough invention that could make hydrogen in automobiles a reality.”

Combustion Research Facility researchers have also been building on Sandia’s long-standing strengths in the study of metal-hydrogen interactions and engine studies to explore hydrogen use for electrical production by stationary power sources — turbines in particular.

Through an overall hydrogen working group, Joe Oefelein (8351) is modeling addition of hydrogen fuel to gas turbine combusters (which typically come online quickly to satisfy spurts in power demand beyond the steady supply of power available from steam turbines). Joe’s collaboration with the National Energy Technology Laboratory in this area has drawn interest from four industry leaders, said Jay Keller (8362).

Meanwhile, CRF researchers are also involved in the International Energy Agency’s efforts to create next-generation models for turbines that can burn hydrogen. The CRF is also seeking funding to demonstrate use of hydrogen fuel, with its near-zero emissions of NOx (smog-producing oxides of nitrogen), in an internal combustion engine, Jay added.

Although one of the biggest impacts of switching to hydrogen from fossil fuel will be seen in transportation, he said, its use in stationery power generation will also help to develop an infrastructure for its distribution and use.