The scoop on fuel cells is that no matter how they’re configured the principle is pretty much the same. They produce electricity by breaking up the atoms of a very basic element, typically… Hydrogen.
First a wee review of atomic structure:
Atoms are made up of 3 types of particles: electrons, protons and neutrons, each with a different property.
- Electrons are tiny, very light particles that have a negative electrical charge.
- Protons are much larger and heavier than electrons and have a positive electrical charge.
- Neutrons have no electrical charge, so we’ll ignore them.
Since electricity is simply the flow of electrons from point A to point B, if we can separate electrons from the Hydrogen (H2) atom, and get them to move, then, hey! We have a source of electricity, right?
How do we separate electrons from the Hydrogen atom?
In one type of fuel cell you cause a chemical reaction that splits off electrons, leaving very lonely positively-charged Hydrogen atoms, called ions, and very excited negatively-charged electrons, behind.
How do you get the electrons to move?
Well, you get oxygen to wag its tail within sight of those lonely Hydrogen ions, which then cozy up to the oxygen and make little water together,
But wait! The electrons don’t want to be left out of the action, so they take the fast lane through a wire for a ménage a trois, on the other side of the fuel cell.
Electricity! And water.
If you stack up a bunch of these things, and runs the electrons through a motor. you might even get enough electricity to power…
(click on the pic – courtesy of the government of Australia – to see a full-size version)
Fuel Cell Notes:
The first fuel cell was built in 1889 by Welsh scientist Sir William Grove. Sir Bill found out that when he immersed separate platinum electrodes in sulfuric acid and then place the other end of each electrode in sealed containers of oxygen and hydrogen, he got a constant flow of current in the circuit. He combined a few cells in a series and thus discovered his “gas battery.”
Fuel cell development of continued more or less as a curiosity for about 75 years. New, better electrodes, electrolytes and reactants were developed. And then, in the ’60s, the U.S space program decided that fuel cells were a lot less risky than nuclear power plants and lighter and more compact than expensive, huge solar panels. Thus, interest in fuel cells as compact and efficient generators of electricity has continued.
For use with cars, the main problems have been expense and durability.
Types of Fuel Cells
Here are some examples of fuel cells, courtesy of About.com… click on the blue links to see a diagram of each.
- Proton Exchange Membrane (PEM) - Efficiency is 40 to 50 percent at about 175 degrees F. Cell output ranges from 50 to 250 kW. The electrolyte is a flexible polymer. Their relatively low operating temperature and flexible electrolyte make them ideal for automotive use.
- Alkaline - Operate at about 70 percent efficiency at temperatures between 300 and 400 degrees F. Cell output range is 300W to 5kW and they use a liquid electrolyte of potassium hydroxide (KOH) and water and can potentially leak.
- Molten Carbonate - Operate at about 60 to 80 percent efficiency at temperatures of about 1200 degrees F. Cell output is about 200 MW. Carbonate ions from the electrolyte are depleted in the reactions and require the injection of additional carbon dioxide.
- Phosphoric Acid - Efficiency ranges from 40 to 80 percent at about 300 to 400 degrees F. Cell output is around 200 kW. The phosphoric acid electrolyte is corrosive to internal cell parts.
- Solid Oxide - Operational efficiency is about 60 percent at temperatures of 1800 degrees F. Cell output is up to 100kW. The solid electrolyte is prone to cracking.