GM and Sandia National Laboratories are initiating a 4-year, $10 million program to develop and to test sodium aluminum hydride (sodium alanate for short) storage tanks for hydrogen. The goal is to develop a pre-prototype solid-state hydrogen storage tank that would store more hydrogen onboard a fuel cell vehicle than possible with current conventional hydrogen storage methods.
Researchers also hope to create a tank design that could be adaptable to any type of solid-state hydrogen storage.
Metal hydrides, which form when metal alloys are combined with hydrogen, can absorb and store hydrogen within their structures. When subjected to heat, the hydrides release their hydrogen.
GM and Sandia say the program is part of a concerted effort to find a way to store enough hydrogen onboard a fuel cell vehicle to equal the driving range obtained from a tank of gas, which will be key to customer acceptance of fuel cell vehicles.
The current leading methods of storage are liquid and compressed gas. However, to date, neither of these technologies has been able to provide the needed range and running time for fuel cell vehicles.
The GM-Sandia project has two phases. In Phase One, the program will study engineering designs for a sodium alanate storage tank. Researchers will analyze these designs using thermal and mechanical modeling, develop controls systems for hydrogen transfer and storage, and develop designs for external heat management. GM and Sandia scientists will also be testing various shapes—from cylindrical to semi-conformable—to see which are the most promising.
In Phase Two, researchers will subject promising tank designs to rigorous safety testing and ultimately fabricate pre-prototype sodium alanate hydrogen storage tanks based on knowledge gained from the program’s first phase.
A possible scenario for filling up with a solid-state storage solution such as sodium alanate could look like this: The alanate would come preloaded in the tank, where it would remain, giving up its hydrogen, and becoming a mixture of sodium hydride and aluminum. The customer would fill up using gaseous hydrogen. During filling, the mixture of aluminum and sodium hydride would absorb the hydrogen and turn it back into alanate, which would be ready to yield hydrogen when needed by the fuel cell. Once the tank is filled, the hydrogen would be stored at low pressure.
Hydride-based hydrogen storage has some hurdles to clear. One current drawback is that most complex metal hydrides, such as sodium alanate, still operate at too-high a temperature, producing an inefficiency that forces some of the hydrogen to be used up in order to release the remaining hydrogen. In other words, because recharging of the hydrides and release of the hydrogen from metal hydrides requires heat, it increases overall fuel consumption. Another challenge is reducing the time it takes to reabsorb hydrogen—currently 30 minutes to recharge.
In separate, independent projects outside of this collaboration, both GM and Sandia are working to identify alloys that will store greater amounts of hydrogen that can be released at lower temperatures. Reducing filling and recharging times is another key area of research.