4.1  Introduction

• Definition: Unlike a battery, a fuel cell is an energy conversion, not an energy storage device. Its prime purpose is to produce a direct current (DC) voltage. 

4.2  History of Early Fuel Cells

• 1838: Principle of the fuel cell was discovered by Christian Friedrich Schonbein (German).
  
  
• 1843: The first fuel cell was developed by William Robert Grove (British). It employed similar material to that found in current Phosphoric-Acid fuel cells (PAFC).
  
  
• 1930s: Tests involving high temperature solid oxide electrolyte fuel cells (SOFC) took place in Switzerland.
  
  
• 1959: Francis Thomas Bacon (British) developed a 5 kW stationary alkali fuel cell.
  
  
• For additional information see Green Cars, Section 8 (Fuel Cell Powered Cars). 

4.3  How A Fuel Cell Works

• A fuel cell works on the principle that when hydrogen and oxygen atoms come together the hydrogen atoms release protons and electrons.
  
  
• Hydrogen, the energy source, is fed to one side of the fuel cell (“the anode”) and oxygen, which the hydrogen reacts with, is fed to the other side (“the cathode”).
  
  
• A membrane or ceramic electrolyte designed to allow the protons, but not the electrons, to pass through it from the hydrogen to the oxygen side, is located in the middle of the fuel cell.
  
  
• The electrons released by the hydrogen are made to flow via an external electrical circuit to reach the oxygen side of the fuel cell and by doing so create the required electrical current.
  
  
• When the protons and electrons combine at the oxygen side of the fuel cell water is produced and expelled from the fuel cell.
  
  
• Note: Fuel cells are used in NASA’s space shuttle and the expelled water is used for drinking.
  
  
• A fuel cell typically produces about 0.7 volts. To create sufficient voltage and current they are assembled together in a “stack”. 

4.4  Types of Fuel Cells

• There are at least 15 different types of fuel cells, designed to meet a variety of applications such as transportation, portable cell phones, laptop computers, power plants, houses, offices, etc.
  
  
• The “Proton Exchange Membrane” fuel cell (PEMFC) is commonly used in vehicles. It has an operating temperature of about 83 degrees C (175 degrees F).
  
  
• When used in a car it is about the size of a medium suitcase.
  
  
• Note: The letters PEMFC are sometimes referred to as the “Polymer Electrolyte Membrane” fuel cell.
  
  
• Oher types of fuel cells include:
  
  
• “Alkali FC” (AFC), which is used by NASA.
  
  
• The “Direct Methanol FC” (DMFC), which uses pure methanol mixed with steam.
  
  
• The Phosphoric Acid FC (PAFC), used mainly for stationary power generation because they tend to large and heavy. 
  
  
• For further information these and the many other types of fuel cells and their uses see Green Cars, Section 10 (Green Web Site Links).