How Fuel Cells Work

The best way to imagine a fuel cell is to imagine a regular chemical battery like that which powers your cell phone or watch. Like a battery, a fuel cell has a “positive” and a “negative” side. The difference between a battery and a fuel cell is that a battery stores power directly through a chemical reaction whereas a fuel cell generates it through a chemical reaction. Like batteries, fuel cells generate direct current (DC).

A fuel cell is made up of two electrodes, a positive (anode) and a negative (cathode). The chemical reactions that create power take place at those electrodes. The electrodes themselves are separated by electrolyte, a chemical that carries electrically-charged particles. The electrodes also have a catalyst, which facilitates and speeds the chemical reactions at the electrodes.

Most fuel cells are small and generate only tiny amounts of power individually. They are combined together in a “fuel cell stack” to work in tandem to create larger amounts of power overall. A fuel cell stack can consist of dozens or even hundreds of individual fuel cells.

How a Hydrogen Fuel Cell Works

There are many options for fuel sources for fuel cells, each useful for different things. Hydrogen fuel cells are the ones most often used in transportation and the ones being explored for use in automotive.

In a hydrogen fuel cell, hydrogen is mixed with oxygen to create water and, during that process, an electron is released to travel an electrical circuit.

This process works in a fairly simple way. Imagine a chamber with an electrode on either side, each surrounded by a catalyst. In the center is a thin membrane of film and filling the whole chamber is a fluid. The electrodes and catalyst are where hydrogen and oxygen are introduced, hydrogen on one side and oxygen on the other. The membrane is called the “proton exchange membrane” and the fluid is the electrolyte that helps speed the flow of the hydrogen and oxygen as they react.

It’s important to remember that electricity always flows in a circuit, so it’s never “one way.” It must be inside a loop. Knowing that, the process becomes simple to understand.

Hydrogen comes in on one side and flows through the anode, where it’s ionized (given a positive charge) by shedding an electron. The ionized hydrogen enters the electrolyte and passes through the proton exchange membrane to the opposing catalyst, through which oxygen is being sent. The ionized hydrogen (H₂) combines with the oxygen (O), helped by its positive charge, and completes its journey by re-combining with the lost electron at the far end of the circuit (at the anode), creating water (H₂O) that flows out an exhaust.

In some hydrogen fuel cell designs, the oxygen receives the loosed electron before combining with the hydrogen. The process otherwise remains the same.

Although the principle behind fuel cells is simple, their design and use can be very complex. Many variables work into how efficient and useful a fuel cell can be and most research is into making them economical, reliable, and powerful enough to be useful as a primary power source for a vehicle.

For more information on fuel cells, see FuelEconomy.gov and AmericanHistory.si.edu.