The Complete Handbook of Fuel Cells

Chapter 1: Understanding Fuel Cells

A fuel cell is an electrochemical device that converts chemical energy stored in a fuel—usually hydrogen, but sometimes methanol or natural gas—directly into electricity and heat, without combustion. Unlike a battery, which stores chemical energy and slowly depletes it, a fuel cell produces electricity continuously as long as fuel is supplied. Unlike a generator, which burns fuel mechanically to spin a turbine, a fuel cell uses an electrochemical reaction to move electrons directly from fuel to oxygen, generating electrical current in the process.

The simplest way to understand what a fuel cell does is to reverse the process you learned in high school chemistry: electrolysis. In electrolysis, you apply electrical current to water to split it into hydrogen and oxygen. In a fuel cell, you feed hydrogen and oxygen into the device, and the chemical reaction releases electrons. Those electrons want to move from the hydrogen to the oxygen, and if you create a path through an external circuit—a load—they do, generating electrical current. After the electrons have done their work, the hydrogen and oxygen recombine as water, the only emission from most fuel cells.

This is not a new idea. Sir William Grove built the first fuel cell in 1839, decades before practical combustion engines existed. But for most of the 20th century, fuel cells remained laboratory curiosities because they were expensive, fragile, and unreliable at anything larger than a watt or two. NASA used them in the Apollo program because reliability and efficiency