For all the volatility of a gas like hydrogen, which combusts with one-tenth the energy required for gasoline, hydrogen fuel cell vehicles are safer than cars with internal combustion engines, according to industry experts.
At last week's Los Angeles Auto Show, several major car companies, including Audi, Honda, Hyundai and Toyota, announced the release of, or updated plans to release, hydrogen fuel cell vehicles this year or within the next two years.
Toyota touted a four-passenger fuel cell vehicle (FCV) called the Mirai, which will begin shipping next month. Audi unveiled the A7 Sportback H-Tron Quattro, a modification of its four-door Quattro coupe that, instead of a traditional drive train, features an electric motor powered by a hydrogen fuel cell.
Meanwhile, Honda, which already leases its FCX Clarity hydrogen FCV in California, announced another concept vehicle that it plans to release in Japan in 2016. And Hyundai has been leasing its Tucson Fuel Cell since June and plans to produce 1,000 of the vehicles this year.
All of the cars are able to fully charge with hydrogen in three to five minutes, compared to the 20 minutes it takes for a Tesla all-electric vehicle (EV) to charge just half way.
A full charge in a Tesla provides up to 265 miles of travel. A Toyota RAV4 EV, gets only 125 miles on a full charge. Hydrogen FCVs, by comparison, can go 300 or more miles on a single charge.
But even though they fill up quickly and can run cars for long distances, hydrogen fuel cells are burdened with a somewhat unfortunate reputation, courtesy of Germany's infamous LZ 129 Hindenburg, the hydrogen-filled airship that exploded over Lakehurst, N.J. in 1937.
Toyota spokeswoman Jana Hartline said hydrogen fuel cells have gotten a bad rap. The perception that they're dangerous is unwarranted, she argued.
"I think it's just our perception of hydrogen being extremely flammable and dangerous compared to what we're comfortable with in this day and age, which is gasoline," she said. "Gasoline is also an extremely flammable fuel, and one that does not escape like hydrogen."
The hydrogen fuel cell tanks in the Toyota Mirai are pressurized up to 10,000 psi, and hydrogen is 16 times lighter than air. So, if a tank were punctured or otherwise compromised, the hydrogen gas would instantaneously dissipate into the atmosphere, Hartline said.
John Kopasz, a scientist at the Argonne National Laboratory who performs research on hydrogen gas production, said that while there are inherent dangers with any combustible fuel, hydrogen fuel is safer than gasoline.
If a regular car's fuel tank is punctured, gasoline leaks out and pools beneath the vehicle, creating a ready source of fuel for a prolonged burn, Kopasz said.
In fact, in the case of the hydrogen-filled Hindenburg, most of the fire was fueled by diesel fuel for the airship's engines and a flammable lacquer coating on the outside of the dirigible.
Today's hydrogen fuel tanks are also made from highly durable carbon fiber whose strength is assessed not only in crash tests but also in trials in which bullets are fired at it.
Toyota reached back to its roots as a loom manufacturer in the early 20th century to create triple-layer hydrogen tanks made of woven carbon fiber.
The tanks, which are lined internally with plastic, underwent "extreme" crash and ballistics testing, Hartline said, noting that they were "shot with bullets that actually bounced off."
"They had to move to high-caliber armor-piercing rounds to pierce the tank, and even then it had to be shot in the exact same spot twice with an armor-piercing bullet," Hartline said.
The Mirai has other safeguards, including structural integrity to protect the tanks and electronic systems that are programmed to shut down any hydrogen lines in the car if a leak is detected. "So there are redundancies upon redundancies," Hartline said. "We're not going to put anything on the road that doesn't meet our safety, quality and durability standards."
Hydrogen is the simplest and most common molecule known to exist. And because of that, it is a part of almost every other substance, such as water and hydrocarbons. Hydrogen is also found in biomass, which includes all plants and animals.
There are several methods for creating hydrogen fuel, but the most common nowadays is via steam-methane reformation, a process by which high-temperature steam (1,000 degrees Celsius) creates a reaction with methane gas in the presence of a catalyst to produce hydrogen, carbon monoxide and a relatively small amount of carbon dioxide. The carbon dioxide and other impurities are then removed through a process called "pressure-swing adsorption," leaving essentially pure hydrogen. Steam reformation can also be used with ethanol, propane or even gasoline to produce hydrogen.
Steam-methane reformation is most commonly used by oil refineries, which then use the remaining hydrogen to remove impurities, such as sulfur, from petroleum and diesel fuels.
Hydrogen can also be produced through electrolysis, or using electricity and a catalyst to create a chemical reaction that separates the hydrogen molecules from oxygen. Solar power can also be used in combination with water and a catalyst (typically a metal) to generate hydrogen fuel by splitting hydrogen molecules from oxygen. Most often, the catalysts are expensive metals, such as platinum (iridium).
"Making hydrogen from natural gas can be done relatively inexpensively," Kopasz said. "Hydrogen made from water electrolysis is a process we've known about for a very long time, but they're still working to bring the cost of that process down. The main cost now is the electricity, but the catalysts are expensive too."
The biggest challenge to hydrogen production today is cost. While hydrogen molecules may be virtually everywhere, separating them from other compounds can be more expensive than refining gasoline. For example, a kilogram of hydrogen gas contains roughly the same energy as a gallon of gasoline, but it costs more than twice as much to produce, according to Kopasz.
A large part of the cost of hydrogen fuel, however, is the lack of existing infrastructure to produce it. That will change as government programs, such as H2USA, push for the development of more hydrogen fuel resources.
H2USA is a new public-private partnership to address the key challenges of hydrogen infrastructure. Its mission is to promote the introduction and widespread adoption of fuel cell electric vehicles across the U.S.
By 2020, the U.S. Department of Energy believes, the cost of hydrogen used in fuel cell electric vehicles (FCEV) will be competitive on a cost-per-mile basis with the fuels used in other types of vehicles, such as the gasoline in hybrid-electric vehicles.
But, the hydrogen fueling infrastructure is in its infancy. Refueling stations are few and far between. California is expected to build 28 stations by the end of 2016, bringing the state's total to 48 stations, according to Hartline. Toyota has partnered with FirstElement Fuel to build refueling stations in California and with hydrogen fuel provider Air Liquide to build a network of 12 stations throughout Connecticut, Massachusetts, New Jersey, New York and Rhode Island next year.
"The advantage of hydrogen fueling stations is that there's really a global standard that doesn't require specific tooling. Cars will be able to refuel anywhere, all the nozzles will be the same," said IHS analyst Devin Lindsay.