Hydrogen fuel-cell cars are starting to make an appearance in the market, but they face a few big hurdles. Price is one, but unfamiliarity is the big blockade. It’s fear of the unknown often keeps us from experiencing things we might actually find enjoyable, even helpful.
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The uncertainty, even fear, about fuel-cell electric cars centers on their compressed hydrogen gas “fuel.”
For many of us, the word “hydrogen” conjures images of explosions and fierce fires.
But fear not. The hydrogen used for fuel-cell electric vehicles (FCEVs) is different from, but likely no more dangerous than, the gasoline most people pump into their cars and trucks without a second thought.
Go Ahead, Light My Fire
Yes, hydrogen is highly flammable, but it also is extremely light – about 14 time slighter than air. So when released from confinement, as would happen if a fuel-cell car’s tank were breached, hydrogen quickly escapes upward into the atmosphere. Its speedy escape is helped by the fact that it is highly pressurized. The common standard today for fuel cell cars is 10,000 pounds per square-inch,
Burning hydrogen – as was proven in testing by the University of Miami (Fla.) in 2001 – shoots straight up, like the flame of a butane lighter. Gasoline, on the other hand, is heavier than air. Its vapors tend to pool near the ground, where they can catch fire and even explode.
Hydrogen can explode as well, if it is kept enclosed in a tight space. For that reason, hydrogen stations usually store the stuff out of doors or in well-ventilated enclosures. And the storage tanks in fuel-cell cars are loaded with sensors and alarms and safety valves to seal-off leaks in case of a breach.
The average gasoline tank holds three to four times the energy of the fuel-cell vehicles’ hydrogen tanks, making it that much more dangerous in a fire or collision.
The fuel tanks for hydrogen are heavily reinforced in order to contain the pressurized gas. In tests that involve firing live ammunition into filled tanks, the gas vented so rapidly that even in tests when it caught fire it was out of the tank before explosive pressure could build up. Hydrogen storage tanks also have repeatedly been proven safe in crash testing.
The University of Miami’s gasoline versus hydrogen test involved breaching the fuel lines of identical vehicles, one equipped with a hydrogen tank, the other with a gasoline tank, and lighting the leaking fuels. The resulting flames caused severe damage to the gasoline-fueled vehicle, while the hydrogen-using vehicle was undamaged as the burning hydrogen shot up and away from the vehicle.
(The flaming wreck of the Hindenburg zeppelin in 1937 is often cited as an example of the dangers of hydrogen. It certainly showed that the gas is highly flammable and probably wasn’t a good choice, safety-wise, as a medium to keep an airship of that era afloat. But that’s no basis for comparing the zeppelin’s painted fabric gas bag of 80 years ago with the heavily reinforced carbon fiber tanks used to contain pressurized hydrogen gas in today’s fuel-cell vehicles.)
The Technical Stuff
Here’s the rest of the hydrogen story – the uneventful part.
It is the most plentiful element on the planet, but it seldom exists all by itself. Typically, hydrogen atoms bond to other things, like oxygen to form water (H2O) or carbon atoms to form various hydrocarbon compounds, including fossil fuels.
Methane (CH4), the main component of natural gas, is made of one carbon and four hydrogen atoms. So natural gas, no surprise, is the most common source of the 9 million metric tons of hydrogen produced in the U.S. each year. Most of it is used in oil refining and for various industrial purposes, but that’s enough of the stuff to keep 20 million or so fuel-cell cars on the road.
It takes a lot of energy to separate the hydrogen atoms from the carbon atoms in natural gas or, in the process called electrolysis, from the oxygen atoms in water, and then to compress it into a gas that is usable in fuel cell cars.
Unlike gasoline or natural gas, hydrogen isn’t a fuel. It is merely an energy carrier. It works in fuel cell cars by releasing its electrons in the presence of a catalyst.
The electrons are the fuel that provides power for the cars’ electric motors. When that job is done they recombine with oxygen in the fuel cell. That forms water, which cools down the cell after it has been heated by the friction of all those hydrogen atoms shedding their electrons. The water, heated to the point it becomes steam, is then expelled through the fuel-cell cars’ tailpipes.
Efficiency, and Appeal
Because it is energy-intensive to make compressed hydrogen gas, fuel-cell electric cars aren’t as efficient as their battery-electric cousins. But they are, in general, much more efficient and environmentally cleaner over the entire the hydrogen production-to-use cycle than are gasoline or diesel vehicles.
The major reason several major automakers – Toyota, Honda, Hyundai and Mercedes-Benz chief among them – believe there is a big opportunity in fuel-cell electric cars is that their hydrogen tanks can be filled in about five minutes, versus the hours it takes to recharge a battery-electric car. FCEVs also can carry enough energy to keep the car going for about 300 miles, versus 80-120 miles for most battery-electric models.
That, the car companies believe, will make hydrogen fuel-cell electric vehicles more appealing than battery-electric cars – once the high costs of manufacturing their fuel-cell and hydrogen storage systems can be tamped down and the price of the cars made more competitive.
But that’s another story.