It has been a two-horse race-gas or liquid-in the quest for the best way to store hydrogen in an automobile. But there may be a third contender: solid metal hydrides.
Energy Conversion Devices, a company best known for developing the nickel-metal hydride battery used in most hybrid cars, has converted a Toyota Prius sedan to run on hydrogen and electricity. The Troy, Mich., company demonstrated the car Aug. 21 in Detroit.
The hydrogen comes from two low-pressure tanks mounted in the trunk. The tanks are filled with metallic powder that acts as a hydrogen sponge, said Energy Conversion Devices Chairman Robert Stempel.
The company claims its two tanks deliver a range of 300 miles for a small car with an internal combustion engine fueled by hydrogen. If true, that would meet a goal set by the U.S. Department of Energy.
Energy Conversion Devices' claims will be scrutinized by the industry. For example, General Motors Corp.'s fuel-cell-powered Hy-Wire vehicle can travel only 100 miles on a tank of hydrogen gas. A 300-mile range would be a breakthrough for any hydrogen-powered car, a GM spokesman said.
With that kind of range, consumers might accept a vehicle powered by hydrogen. In turn, that would create a demand for more public hydrogen filling stations.
Many experts agree that some sort of interim technology-such as internal combustion engines that burn hydrogen-are needed to provide the transition from gasoline to hydrogen.
A car such as the Prius, which is powered by an internal combustion engine plus an electric motor, could provide that interim step. That would pave the way for mass-produced hydrogen-powered fuel-cell cars sometime around 2020.
How it works
Energy Conversion Devices' storage tanks are charged with a total of 1,500 pounds of gaseous hydrogen. When heat is applied to the metallic powder that acts as a sponge inside the tank, hydrogen is released.
Then the hydrogen is burned in the Prius' tiny piston engine. On a fuel cell vehicle, the hydrogen would be used to power the fuel cell stack to make electricity for the electric motor.
The two tanks weigh 450 pounds each. Six kilograms of hydrogen stored this way roughly is equal to six gallons of gasoline. Energy Conversion Devices claims its Prius gets about 49 mpg in city driving.
If the tanks perform as well as Energy Conversion Devices claims, they would increase the range of fuel-cell vehicles significantly.
Today's handful of experimental fuel-cell vehicles are equipped with tanks that hold hydrogen at 5,000 or 10,000 pounds per square inch. Most travel less than 150 miles before running out of fuel.
Energy Conversion Devices modified the Prius not to showcase the car's performance but to demonstrate its solid hydrogen storage system.
``There are other ways to move to on-board hydrogen storage,'' Mr. Stempel said. GM and other auto makers also are researching solid hydrogen storage systems.
But no auto maker has demonstrated a working vehicle.
All three hydrogen storage systems have technical drawbacks. With Energy Conversion Devices' system, heat has to be applied to its tanks. Cold-weather performance is unknown, and the vehicle requires complex plumbing to feed hydrogen to the engine.
The two rival systems have their own problems. Tanks that store hydrogen gas require high pressure and have limited range. Vehicles powered by liquid hydrogen enjoy good range but are difficult to refuel.
Ford Motor Co. and BMW A.G. have built test vehicles with hydrogen-fueled internal combustion engines. The Ford Focus uses gaseous hydrogen while the BMW 7-series sedan uses liquid hydrogen.
Energy Conversion Devices, which has joint ventures with ChevronTexaco Corp. and General Electric Co., has dabbled with advanced batteries and photovoltaic, or solar, cells.
Last year, the company reported revenues of $90 million.
The company hopes to license its hydrogen fuel system for use in fuel-cell vehicles and cars with hydrogen-powered internal combustion engines.