Fuel cells are a bit like a cross between an internal-combustion engine and battery power. Like an internal-combustion engine, they make power by using fuel from a tank (though the fuel is pressurized hydrogen gas rather than gasoline or diesel). But, unlike an engine, a fuel cell doesn’t burn the hydrogen. Instead, it’s fused chemically with oxygen from the air to make water. In the process, which resembles what happens in a battery, electricity is released and this is used to power an electric motor (or motors) that can drive a vehicle. The only waste product is the water…
Hydrogen is not, itself a fuel, but simply a way of transporting fuel made by some other process. So it’s better to compare it to batteries (another way of packaging and transporting energy) than to gasoline (a genuine fuel).
How does a fuel cell make electricity from hydrogen?
What happens in a fuel cell is called an electrochemical reaction. It’s a chemical reaction, because it involves two chemicals joining together, but it’s an electrical reaction too because electricity is produced as the reaction runs its course.
A fuel cell has three key parts similar to those in a battery. It has a positively charged terminal, a negatively charged terminal, and a separating chemical called an electrolyte in between the two keeping them apart. (Think of the whole thing as a ham sandwich. The two terminals are the pieces of bread and the electrolyte is the ham in between.) Terminals are the pieces of bread and the electrolyte is the ham in between.)
Here’s how a fuel cell produces electricity:
- Hydrogen gas from the tank feeds down a pipe to the positive terminal. Hydrogen is flammable and explosive, so the tank has to be extremely strong.
- Oxygen from the air (big turquoise blobs) comes down a second pipe to the negative terminal.
- The positive terminal is made of platinum, a precious metal catalyst designed to speed up the chemistry that happens in the fuel cell. When atoms of hydrogen gas reach the catalyst, they split up into hydrogen ions (protons) and electrons. In case you’re confused: hydrogen ions are simply hydrogen atoms with their electrons removed. Since they have only one proton and one electron to start with, a hydrogen ion is the same thing as a proton.
- The protons, being positively charged, are attracted to the negative terminal and travel through the electrolyte towards it. The electrolyte is a thin membrane made of a special polymer (plastic) film and only the protons can pass through it.
- The electrons, meanwhile, flow through the outer circuit.
- As they do so, they power the electric motor that drives the car’s wheels. Eventually, they arrive at the negative terminal too.
- At the negative terminal, the protons and electrons recombine with oxygen from the air in a chemical reaction that produces water.
- The water is given off from the exhaust pipe as water vapor or steam.