In a move to extend the range of fuel-cell vehicles that emit no pollution, DaimlerChrysler has built several hydrogen fuel-cell vehicle prototypes with higher-pressure fuel tanks, a research director said Thursday.

Most prototypes currently have 5,000 psi (pound-force per square inch) tanks, which provides a range of between 100 miles and 180 miles.

But several manufacturers have said they plan to introduce 10,000 psi tanks in the future, in order to get more hydrogen into the vehicle. Those cars would run at least 300 miles before the next refueling.

Christian Mohrdieck, a research director at DaimlerChrysler, said the company is getting closer to that goal, having developed several prototypes with 7,000-psi tanks, which would offer a higher range than what’s currently available.

“Range is a problem today, but I think we can solve the problem,” he said. “Our next generation will be 10,000 psi, and will have a range of at least 400 km, or 300 miles, which I think is close to acceptable.”

DaimlerChrysler already has permission to use 10,000-psi tanks in Germany, he said.

Fuel cells produce power by mixing fuel with air and water between a reactive film membrane in an electrochemical reaction. They are seen as a potentially clean replacement for the internal combustion engine, with hydrogen replacing gasoline and diesel.

Fuel-cell vehicles emit no pollutants, releasing only water as a byproduct.

But the clean technology is not yet ready for commercialization, and manufacturers have different estimates on when fuel-cell vehicles can be commercialized. General Motors, for instance, has set a goal of launching them by 2010, while Volkswagen says it will take at least 20 years before they are commercially viable.

LimitedRange

A limited range is just one of the barriers to commercialization that include the high price of fuel cells, the low fuel efficiency in the fuel cell stacks, and the lack of infrastructure to provide the fuel.

At the Road Rally, a three-day event traveling to various Northern California cities that began Thursday, cars from DaimlerChrysler, General Motors, Toyota, Ford, Honda, Hyundai, Volkswagen, and Nissan were available for test drives. Most have a range between 100 miles and 180 miles, and both GM and DaimlerChrysler say they are aiming for at least a 300-mile range to be comparable to conventional cars.

Manufacturers are trying several different approaches to solving the range issue. The problem is that hydrogen weighs a third as much as gasoline providing the same energy, but takes up at least four times as much space.

Because car makers don’t want to quadruple the size of the fuel tanks, some are experimenting with liquefied hydrogen, which has a higher energy density and can give cars a longer range.

But liquefied hydrogen needs to be kept cold, posing refueling and distribution challenges. What’s more, the process of heating the hydrogen to a usable temperature takes up so much energy that much of the fuel is wasted.

General Motors has also been experimenting with solid metal hydride materials, metal alloys that release hydrogen when they’re heated.

But a number of manufacturers, including Nissan, Honda, and of course DaimlerChrysler, are focusing on raising the pressure in the tanks, to force the hydrogen molecules closer together.

“The main ingredients to achieve higher range is higher pressure, a better package so there’s more space for fuel tanks in the vehicles, and even higher efficiency in the fuel cells,” Mr. Mohrdieck said.