Hydrogen power for vehicles sounds tempting: water is the only emission, and hydrogen is seemingly available everywhere, right?


Hydrogen can power vehicles, but how it powers them makes all the difference. Hydrogen-combustion engines are very different than hydrogen fuel-cell vehicles, and Jason Fenske of Engineering Explained breaks both down in a video.

The biggest reason why hydrogen-combustion engines are no good? They create nitrogen oxide, which isn't good for people or the environment. Even though carbon isn't part of the hydrogen combustion process, NOx isn't a compromise as automakers look to zero-emission vehicles.

Second, hydrogen-combustion engines aren't as efficient as a hydrogen fuel cell in numerous ways. By the time hydrogen makes its way to the engine, through a transmission, and into a differential to power a car's wheels, only 25 percent of the hydrogen's potential energy is transferred. In a hydrogen fuel cell, the hydrogen works its way to the fuel cell where electrons are sent to a converter, then to a power control unit, and to an electric motor. The motor then powers a gear reduction to power the car's wheels. Despite numerous transfers, the hydrogen's fuel energy is more effectively transmitted to the wheels, up to 50 percent according to Fenske.

In a basic sense, fuel cell-powered cars are electric cars powered with hydrogen. 

The efficiencies have a cascading effect, too. Since hydrogen takes up a lot of space when in storage, hydrogen fuel cell-powered cars can have smaller fuel tanks compared to hydrogen-combustion cars. And since hydrogen isn't exactly cheap, the fuel cell is far more efficient to operate and uses 25 percent less energy to do the same work as a hydrogen-combustion engine.

If you're itching for more hydrogen information and how it powers fuel cells and engines alike, click play above.