TVN Polymer Electrolyte Membrane (PEM) fuel cells are considered the front runner to replace the highly polluting internal combustion engine in automotive vehicles. A PEM fuel cell is an electrochemical device that uses hydrogen and oxygen to produce electricity. The fuel cell is made of a membrane and electrode assembly (MEA), sandwiched between two current collectors/flowfields. Hydrogen is oxidized to produce protons and electrons, which creates an electric current. Oxygen is reduced, consuming the protons and electrons produced by the hydrogen oxidation. The only byproducts of the reaction are water and heat. Besides the advantage of being a zero emissions power source, the PEM fuel cell is also much more efficient than current combustion technologies. The PEM fuel cell also has the ability to operate on existing fuels. If a partial oxidation reactor is added to the system, the fuel cell can operate on reformed hydrogen from fuel with an existing infrastructure, like gasoline, methanol, ethanol, etc.

The basic operation of the fuel cell can be seen in the figure at right. Hydrogen gas () diffuses from a bulk stream to through the anode gas diffusion layer to the anode catalyst layer. At the catalyst layer, the hydrogen is oxidized, losing its electrons, which are transported out of the fuel cell to perform electric work. The remaining proton attaches to a water molecule to form a hydronium ion (+) and is transported across the membrane. Once the hydronuim ion reaches the cathode catalyst layer, it reacts with oxygen () that has diffused through the cathode gas diffusion layer and the electrons returning from the external electric circuit to form water (). So the end result is that hydrogen and oxygen have reacted to form electricity and water.