There are two ways to make hydrogen cars. It can be used in an internal combustion engine to produce hydrogen or in a fuel cell that powers the electric motors.
(Hydrogen-powered, dual-fuel Mazda RX8
The former format was popular because it could also be used for gasoline. Two tanks were used for gasoline and hydrogen in many of the hydrogen-using platforms. The only thing that limits the utility of a platform is hydrogen storage. This is because it tends to be very heavy. Because hydrogen’s energy density is lower than gasoline, it has a poor fuel economy. And since commercial hydrogen is often ‘cracked’ from natural gas or methane/ethane/propane, it seems rather silly to put up with these issues when you could simply run the vehicle on natural gas or liquified propane.
(Cee-En-Gee, it’s a Chevee!)
The same issues as hydrogen, compressed gas requires high-pressure tanks and heavy pressure storage. Propane, however, requires less sophisticated, though still pressurized, storage. My experience with a propane car was that the power output is almost identical to gasoline. However, if the engine is tuned for propane (which has a higher effective octane), the difference disappears. Propane is easy to deploy for gasoline vehicle fleets, despite its lower energy density. It is also more practical than converting propane to hydrogen.
(Toyota Mirai, Press Photo: I do have firsthand photos of a Mirai somewhere, but it’s buried deep, deep, deep in my photo folders…)
Toyota’s Mirai has used hydrogen in a fuel cell to power an electric motor. This is a more efficient method. Because the fuel cell is faster than lithium ion battery batteries in charge and discharge, you get more range and output from a smaller cell. Although the Mirai does have a hybrid system, which also includes Toyota’s nickel battery pack for around-town cruising, it still boasts excellent fuel economy and is far more efficient than hydrogen-burning cars.
Fuel cells are expensive and require costly catalysts. A Mirai is more expensive than a pure-electric and costs around twice as much as a hybrid. And hydrogen production still isn’t green. Although fuel cell costs have dropped a lot, and they may be priced competitive with lithium-ion batteries in the future, there is a good chance that we will still need to crack natural gas to make hydrogen. It is cheaper to build. More fuel efficient. More durable energy storage. The popularity of this format has resulted in better economies of scale. They are also very competitive with gasoline when used in hybrids.
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