Fill 'er up -- with hydrogen.

It may still sound like science fiction to some. But Japan is taking a lead in making zero-emissions hydrogen-fueled cars a reality.

It's part of the country's aspiration to cut its carbon emissions 80 percent by 2050; nearly a quarter of those emissions come from transportation. And it's a more urgent task in a country that imports all of its oil.

Japan leads Asia in early hydrogen-car infrastructure and is a world-beater in emerging fuel cell technologies.

"Hydrogen is still in very, very early days," cautions Ashvin Chotai, London-based managing director of Intelligence Automotive Asia. "But in the area of green cars, Japan has been investing a lot further ahead than the Western companies in the last few years, and they have an edge."

Take Toyota. Last year they announced they hope to retail an "affordable" fuel-cell car by 2015. It would be next step toward what the firm calls the "ultimate eco-car," after today's popular hybrids like the Prius, the "plug-in" hybrids that just came on the market, and fully electric vehicles.

Long term, Toyota sees hydrogen-fueled cars as ideal for long-haul driving, with plug-in hybrids better for mid-range driving and electrics best for short-range commuting.

That's because fuel-cell cars have a much longer range from one fueling: more than 500 miles already, in a test run of a Toyota vehicle last year in Japan, compared to a maximum 125-mile per charge range with electric vehicles.

Building hydrogen highways

But as with electric vehicles, the biggest hurdle is a lack of power stations. "Fueling infrastructure is the joker in the whole thing," says Toyota spokesman Paul Nolasco. "You can't have fuel cell vehicles without the infrastructure, and you can't have infrastructure without fuel cell vehicles."

The Japanese government is stepping in to address that chicken-and-egg problem. It's subsidizing fuel cell development and collaborating closely with energy and auto companies to build Japan's "hydrogen highway" of the future.

The government has subsidized 13 hydrogen stations for fuel-cell cars, covering at least half of the $5 million to $6 million per station cost, according to the Fuel Cell Commercialization Conference of Japan (energy firms have ponied up the rest). It hopes to build 40 to 50 more by 2015.

Japanese energy firms are actively working together with the government to build the hydrogen car infrastructure. Tomohide Satomi, of the Fuel Cell Commercialization Conference of Japan, says such firms are looking into the future and seeing a need to develop new products as gas sales decrease.

"To survive, they have to change the portfolio of their energy supply business," Mr. Satomi says. "So they're looking to the future. They have to seek new business areas besides gasoline."

He says Japan's hydrogen highway efforts are on par with those in the United States (particularly California) and Germany, and that it leads Asia, with South Korea close behind.

Not cheap, or 100 percent clean

At one such station in a harbor-side, industrial area of Yokohama City, the Japan Automobile Research Institute's Hideaki Matsushita showed off a fuel-cell demo model from Toyota. After a test drive, the car came to rest and a pool of water puddled under the exhaust pipe.

In fuel-cell vehicles, hydrogen fuel and oxygen flow over a fuel cell stack, producing the electricity that runs the motor; the byproduct is water. It's not a 100 percent "clean" energy source: currently one of the cheapest ways to produce hydrogen fuel uses natural gas.

Producing such fuel by "electrolysis" (combining electricity and water to create hydrogen) is the Holy Grail of green vehicles, but that's an exorbitant process for now.

At the Yokohama demo station, it's clear that fuel-cell vehicles aren't quite ready for prime time. The ideal customer is a millionaire – and a bodybuilder. For safety reasons, the pumping of high-pressure hydrogen fuel requires a heavy, rugged case and nozzle. A mechanical arm helps lift the nozzle to the car for fueling.

And a typical fuel-cell vehicle goes for about $1 million, according to Sayaka Shishido, of NEDO, the government's funding arm for fuel cell and other "new energy" development projects. Toyota leases its 14 fuel-cell vehicles in Japan for a cool $9,000 to $11,000 per month, to universities and local governments.

Target year: 2015

Ten years ago, the Japanese government hoped to have five million fuel cell cars on the roads by now. Satomi said that cost and durability issues were greatly under-estimated.

The new goal is more realistic, with a focus on building the necessary infrastructure for very small-scale commercialization by 2015.

Aside from infrastructure, other technical hurdles remain. One focus now is reducing the amount of expensive platinum used in each car. Many fuel cell vehicles now use around 100 grams; the goal is to whittle that down to just 10 grams.

Toyota says it's making progress: It has doubled the capacity of its hydrogen tanks in the past year, and sharply reduced the platinum it uses per car, to under 50 grams.

NEDO is funding research on reducing costs and improving fuel-cell durability. And it's confident about its commercialization targets, because auto and energy companies are on board.

"2015 – that will be the key year for Japan," says NEDO's Ms. Shishido. "This will be the starting year for utilization of fuel-cell vehicles by the general public.”