Storing Hydrogen Safely
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| Storing hydrogen safely onboard personal transportation vehicles is a major callenge for the hydrogen economy envisioned for the 21st century. |
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Metal hydrides could potentially play a leading role in a hydrogen economy. By Virginia
Heffernan
Nickel magazine, October 2002 -- Shell is preparing for a new "hydrogen economy" by teaming
up with two other major companies to develop products that use metal hydrides to store hydrogen.
The initiative puts metal hydrides, including some that use nickel, at the forefront of efforts to establish safe and reliable hydrogen storage, one of the weakest links in the chain from research to commercial application of fuel cell technology.
The advantages of using nickel in these types of applications include the metal's hydrogen storage properties and tolerance of impurities.
As fuel cell development progresses worldwide, hydrogen, which creates few or no emissions, promises to become a clean energy source for everything from cars to stationary power plants.
But storing hydrogen is a challenge. The gas takes up a lot of space (for example, the amount required to run an electric car on a fuel cell for 400 kilometres would fill a balloon 5 metres in diameter), and compression, the obvious solution at first glance, can be dangerous because of hydrogen's volatility.
So the race is on to develop a new means of storage that is both safe and convenient. HERA Hydrogen Storage Systems, a joint venture between Shell Hydrogen, Gesellschaft für Elektrometallurgie (GfE) and Hydro-Quebec, believes the future lies with metal hydrides, which are binary compounds formed by hydrogen and another element (usually more electro-positive) or group, such as sodium hydride or methyl hydride.
Metal hydrides literally trap hydrogen within the alloy, much like a sponge absorbs water. When heat is applied, the gas is released. Hydrides are capable of storing hydrogen at two or three times the density of compressed gas and will desorb the hydrogen at roughly the same pressure required for storage.
U.S.-based Ergenics currently offers safe, low-pressure storage of hydrogen in canisters that can be charged and discharged more than 100,000 times. The units use Ergenics' patented Hy-Stor 208 alloy, MNi4.5Al0.5.
But to improve the performance of these storage systems, researchers must find ways to increase the proportion of hydrogen in the hydrides, whilst maintaining the reversibility of the reaction within a reasonable temperature and pressure range. Many alloys form hydrides with up to 9% hydrogen but will release the gas only at extreme temperatures.
HERA's research team is scrutinizing three main groups of alloys: magnesium-based high temperature hydrides, chemical hydrides, and medium-temperature alanates.
Although metal hydrides are generally too heavy for use in mobile applications such as cars and buses, they show promise for stationary power generation for homes and businesses, says Marc Hubert, director of business development at HERA. For example, the magnesium hydrides can store up to 6.5% hydrogen.
"Magnesium-based hydrides can store four to five times as much as conventional alloys," he says. "But they require more energy at a higher temperature. We have not yet found many applications where that amount of heat is available to release the hydrogen."
Longer-term, medium-temperature alanates, which use the lightest elements in the periodic table, may prove suitable for hydrogen storage in vehicles, he says, but research on these compounds is still in the early stages.
Another potential solution is composite alloys that combine the best storage properties of two different
metals. For example, magnesium has been mixed with hydrides that show fast kinetics, such as
LaNi5. In this case, nickel acts as a catalyst for the dissociation of molecular hydrogen.
Virginia Heffernan is a Toronto-based freelance science
writer(www.geopen.com).
Marc Hubert Director, Business Development HERA Hydrogen Storage Systems 1790 Lion-Boulet, Varennes, Quebec Canada J3X 1S1 Tel: 1-450-652-8312 Fax: 1-450-652-8388 E-mail: mh@herahydrogen.com Website: www.herahydrogen.com |
