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How They Work: Fuel Cell Systems
PEM fuel cells are the center of an integrated propulsion system-one that is radically different from conventional vehicle systems. The diagram below shows the basic components of a hydrogen-fueled FCV.
How They Work
PEM Fuel Cells
Hydrogen Sources

Fuel Cell Systems

Diagram: Location of various components in a FCV.

Roll your mouse over each of the components
in the diagram below to learn more.

Roll your mouse over the image to the left to learn more.
The amount of electricity a fuel cell produces depends on how much fuel (hydrogen and air) is supplied to it. The air compressor controls the rate at which air is supplied to the stack according to the need for power.
The fuel cell stack uses hydrogen gas and air to produce electricity to power the electric motor. This "stack" typically consists of over 400 individual fuel cells.
The Power Controller Unit (PCU) contains sophisticated electronics that manage the production and storage of electricity.
For FCVs using pure hydrogen as a fuel, the hydrogen is generally stored as a gas in high-pressure tanks, so that enough fuel can be stored to give the vehicle a suitable driving range. In most current FCVs, the fuel tank is capable of storing hydrogen at 5,000 lbs/in2, although higher-prssure tanks are currently under development.
Some FCVs employ a battery to store electricity produced from regenerative braking or from the fuel cell stack. The stored electricity can be used to help power the electric motor or other electrical devices.
An FCV can be powered by one or several electric motors--some use a separate electric motor for each wheel. These motors produce enough power to propel FCVs at speeds comparable to those of conventional vehicles.

FCVs like the one above use pure hydrogen as fuel, stored onboard the vehicle in highly pressurized tanks. Other FCVs are designed to use a liquid fuel such as gasoline or methanol, which is stored in a conventional, non-pressurized tank. FCVs using these fuels also need a reformer-a fuel processor that breaks down the fuel into hydrogen for the fuel cell, carbon dioxide, and water. Although this process generates carbon dioxide, it produces much less than the amount generated by gasoline-powered vehicles.

Fuel cell vehicles can also be equipped with regenerative braking systems that capture the energy usually lost during braking and store it in an up-sized battery.