Technology

How Fuel Cells Work

Pressurized hydrogen gas enters the fuel cell on the anode side. This gas is forced through the catalyst by the pressure. When a hydrogen molecule comes in contact with the platinum on the catalyst, it splits into two positive hydrogen ions and two electrons. The electrons are conducted through the anode, where they make their way through the external circuit (doing useful work such as turning a motor) and return to the cathode side of the fuel cell.

Meanwhile, on the cathode side of the fuel cell, oxygen gas is being forced through the catalyst, where it forms two oxygen atoms. Each of these atoms has a strong negative charge. This negative charge attracts the two positive hydrogen ions through the membrane, where they combine with an oxygen atom and two of the electrons from the external circuit to form a water molecule.

This reaction in a single fuel cell produces only about 0.7 volts. To get this voltage up to a reasonable level, many separate fuel cells must be combined to form a fuel-cell stack. These fuel cell stacks power the car.

PEMFCs operate at a fairly low temperature (about 176 degrees Fahrenheit, 80 degrees Celsius), which means they warm up quickly and therefore don't require expensive containment structures. Improvements in these fuel cells have increased the power density to a level where a fuel-cell stack about the size of a small piece of luggage can power the car.