"Heat it up and hydrogen comes out, cool it down and the hydrogen goes back into the metal hydride
," said Kim.
He notes that sodium-borohydrides have far greater hydrogen absorption potential than conventional metal hydrides: NaBH4, according to Suda, can generate up to 10.8 percent of hydrogen by hydrolysis on a weight basis (i.e., the weight of stored hydrogen as a percentage of the weight of the total storage system).
He also does not feel it is possible to reduce fuel cell and/or vehicle weight sufficiently to compensate for storage limitations of metal hydrides and compressed hydrogen.
"As a result," he says, "NaBH4 has a weight, size, cost and power control advantage over metal hydride mad liquid hydrogen and a weight, size and cost advantage over pressurized hydrogen."
To make a silent artificial muscle, Kim and his colleague Alexandra Vanderhoff first compressed a copper and nickel-based metal hydride
powder into peanut-sized pellets.
"We are creating the design tools and gaining the expertise needed to design hydride beds for future storage tanks," says Jim Spearot, director, Chemical and Environmental Sciences, GM R & D, "and refining the solid-phase storage material requirements." This will lead to building and testing a full-size metal hydride
storage tank using sodium alanate or a higher performance material in the near future.
As the hydrogen gas is absorbed during charging, the metal hydrides generate heat that is removed by water.
Because of ChevronTexaco's international presence, the joint venture is also working on hydrogen service stations using metal hydrides for hydrogen bulk storage.
Among the advantages metal hydride has in fuel storage is its compactness.
The metal hydride is contained in compartments inside the storage "pressure vessel." Hydrogen gas is pumped into the vessel at high pressure and absorbed by the powder.
According to Mudawar, "This process is reversible, meaning the hydrogen gas may be released from the metal hydride by decreasing the pressure in the storage vessel."
"The acquisition of Ergenics will accelerate [the commercialization] initiative by adding over 20 years of product development expertise in the application of metal hydride
materials," said van Zeyl.