Fuel cell

A fuel cell is an electrochemical device that converts a fuel's chemical energy directly into electricity. Fuel cells have no moving parts and are similar to batteries except that while batteries only store energy, fuel cells produce energy continuously given a supply of fuel. Fuel cells can run on various fuels including natural gas, biogas, methanol, ethanol, and hydrogen.

Diagram of a simple fuel cell using hydrogen fuel

A fuel cell typically contains two electrodes separated by an electrolyte solution or matrix. The electrodes are porous meaning they allow gases to pass through. The fuel is fed into one electrode and oxygen or air is fed into the other electrode. The electrode on the fuel side contains a chemical catalyst that breaks the fuel compound into individual atoms consisting of positive ions and electrons. The positive ions transfer through the electrolyte to the other electrode where they combine with the oxygen or air. Meanwhile, the electrons travel through the external circuit to the other electrode. It is this flow of electrons that creates useful power.

There are different types of fuel cells. Fuels cells are classified by the materials used including the type of electrolyte and/or type of catalyst. Main types include polymer exchange membrane fuel cell (PEMFC), solid oxide fuel cell (SOFC), alkaline fuel cell (AFC), molten-carbonate fuel cell (MCFC), phosphoric-acid fuel cell (PAFC), and direct methanol fuel cell (DMFC). Each type has its own characteristics that make it more or less useful for specific applications.

Hydrogen fuel cell stack in the Energy Systems Integration Lab at the National Renewable Energy Lab (NREL)
Hydrogen fuel cell at the National Renewable Energy Lab
Photo by Dennis Schroeder courtesy of NREL