The current conventional wisdom is that plug-in electric vehicles will be the clean, sleek cars of tomorrow. Think of Tesla’s Model S or Nissan’s Leaf. These cars get most of the media attention, and policymakers tend to toss tax breaks their way.

Not all automakers, however, are persuaded that plug-ins are the only way to go. This month, Honda, Toyota and Hyundai all announced plans to produce hydrogen fuel-cell passenger vehicles in the next few years. These cars will run on compressed hydrogen — and emit only water vapor as exhaust.

For a long time, hydrogen fuel-cell vehicles were seen as a tantalizing technology to help reduce society’s reliance on oil. In theory, fuel-cell vehicles could charge in minutes and go for hundreds of miles before refueling — overcoming the disadvantages of plug-in electric cars with their bulky batteries and limited ranges.

But the vehicles themselves were seen as forbiddingly expensive, and the challenges in setting up a hydrogen fueling infrastructure looked insurmountable. That explains why hydrogen lost its allure in the 2000s, particularly as batteries improved and electric vehicles became a reality. In 2009, the U.S. Department of Energy shifted its research and funding away from hydrogen and toward battery-driven electric cars.

Now the pendulum may be swinging back. Plug-in electric cars aren’t selling quite as well as their advocates once hoped. And the cost of hydrogen fuel-cell vehicles seems to be dropping. Could hydrogen be in for a comeback? Or are the obstacles still too steep?

Toyota’s emphasis on hydrogen is especially noteworthy. Sixteen years ago, the Japanese automaker was the first company to produce a commercially successful hybrid-electric car — the Prius, which features both a gasoline engine and an electric motor whose battery is charged by braking energy. That success led to a rising interest in electric cars.

Yet Toyota isn’t focused on all-electric vehicles as the logical next step. “The reason why Toyota doesn’t introduce any major [all-electric vehicles] is because we do not believe there is a market to accept it,” said Toyota Chairman Takeshi Uchiyamada during a speech in Washington back in September.

Uchiyamada argued that battery technology still needs a few major breakthroughs before all-electric vehicles can compete with hybrids or traditional gasoline-powered cars — the batteries are expensive, have limited range and take hours to recharge fully. So, for now, Toyota will focus on improving its line of hybrids to meet rising fuel-economy rules.

But the company is also betting on hydrogen. Toyota is promising a mass-produced fuel-cell vehicle in Japan by 2015 and one in the United States by 2016. The price? Between $50,000 and $100,000. That lower end is comparable to the cost of Toyota’s Lexus sedans — and it’s cheap enough that hydrogen vehicles could, potentially, have mass appeal.

Other automakers agree that fuel-cell vehicle costs are falling dramatically. “These things are now ready for prime time,” John Krafcik, Hyundai’s North American chief executive, recently told the Associated Press. But is that enough to edge out plug-ins?

Hydrogen fuel cells use a chemical process to separate out the electrons in molecules of hydrogen gas that, in turn, power the car’s electric motor.

The main advantages of hydrogen fuel-cell vehicles: They can charge within minutes and have a longer range than plug-ins. Toyota estimates that its fuel-cell cars will travel 375 miles before refueling. That’s a huge deal.

So, what’s the catch? For starters, there are very few hydrogen fueling stations around the country. And building out a network could prove difficult. One 2008 study by the National Academy of Sciences estimated that it could require $55 billion of public investment just to get 2 million hydrogen cars on U.S. roads by 2023.

As of 2012, there were 13,392 electric-charging stations around the country, compared with just 58 hydrogen stations.

There are also potential environmental drawbacks to fuel cells. The hydrogen gas first has to be split off from water, then transported to fueling stations, then condensed at high pressures, and then converted back into electricity inside the car. That’s a fairly inefficient process.

In the near term, natural gas would likely be used to produce all that hydrogen. If so, fuel-cell cars could actually produce more greenhouse-gas emissions than many gasoline-powered vehicles when you consider the entire life-cycle. Fuel cells might not be a truly “green” technology until the world has a surplus of carbon-free energy to produce hydrogen — a prospect that’s still a ways off.

Both battery and hydrogen vehicle technologies have their advocates and detractors. Elon Musk, the founder of Tesla, has argued that there’s “no way” fuel cell technology will ever prevail, citing cost and environmental concerns. Toyota’s officials, however, argue that Tesla’s success with electric vehicles is “a rare case” — and that the future lies elsewhere.

But it’s also possible that a variety of technologies could find their own particular niches in the decades ahead. Hybrids could dominate as a fuel-efficient “bridge” to the future, as Toyota’s Uchiyamada has predicted. Meanwhile, battery costs could tumble, making plug-in electric cars more viable for short commutes. And hydrogen vehicles could catch on for long-haul trips. Right now, however, it’s still unclear how this battle will shake out.