How a Hydrogen Fuel Cell Automobile Works

Hydrogen fuel cells convert chemical energy into electricity.

Hydrogen fuel cells convert chemical energy stored in bonds between hydrogen and oxygen atoms into electrical energy. The electrical energy in turn powers the car.

Features

Pure hydrogen gas is scarce on Earth, so hydrogen must be produced from other sources --- often methane. Hydrogen is stored in the fuel tank as a compressed gas or in a liquid form.

Function

In the fuel cell, hydrogen molecules enter at one end and are ionized, or stripped of electrons. The resulting protons flow through a membrane that permits the passage of protons but not electrons. The electrons, meanwhile, are picked up by an electrode and flow through a circuit as electric current to rejoin the protons on the other side of the membrane. The passage of the electrons through the external circuit generates current used to turn a motor and provide power to the car.

Considerations

A single fuel cell produces only a 1-volt electric potential, so many fuel cells are typically combined to produce sufficient power to drive the car. The maximum amount of energy extracted from the fuel is the same as if the hydrogen were simply burned in the presence of oxygen at high temperatures; fuel cells, however, convert chemical energy into electricity, while combustion releases heat, which combustion engines convert into mechanical work.

References

• Department of Energy Hydrogen Program: Hydrogen Fuel Cells
• Department of Energy Renewable Energy: Fuel Cell Technologies Program
• "Essential Environment, The Science Behind the Stories, 2nd Edition"; Jay Withgott and Scott Brennan; 2007