Fuel-cell vehicles are basically electric cars that use hydrogen fuel cells to generate electricity for power, with water or water vapor being the only byproduct. FCVs don't emit pollution or greenhouse gases and are about twice as efficient as gasoline engines.

A typical FCV holds hydrogen gas in a tank. It feeds the fuel cells, which combine the hydrogen with oxygen from the air in a chemical reaction to create electricity. That runs the electric motor, which turns the wheels.

Many newer FCVs have backup batteries or capacitors for an extra burst of acceleration when needed and to store energy recaptured during braking.