Electro-Chem-Technic :: Solid Polymer Fuel Cells

Solid Polymer Fuel Cells - Acid Electroyte Fuel Cells:

In both acid electrolyte and solid polymer fuel cells the electrolyte contains mobile H+ ions. The most common acid fuel cell is the Phosporic Acid Fuel Cell. A standard solid polymer electrolyte is Nafion.

It is these H+ ions that play a key role in the reactions within the cell.

At the anode, hydrogen gas is ionised, producing free electrons and H+ ions:-

The electrons go round the external circuit connected to the fuel cell, and reach the cathode. The H+ ions move through the elctrolyte, and also reach the cathode.

At the cathode the H+ ions and electrons react with the oxygen, producing water:-

This movement of ions through the electrolyte, and movement of electrons round the external circuit is illustrated in the diagram below:-

Note three important points:-

1. Water is produced at the cathode. (In the alkali fuel cell it is produced at the anode.)

2. The anode is the electrically negative terminal. Some people find this surprising, since they are wrongly taught that anode always means positive. It does not! The anode is also the correct name for the negative terminal of any primary cell. (See the Oxford English Dictionary!)

3. The electrolyte in a solid polymer fuel cell is often called a "Proton Exchange Membrane", or PEM. This is because it is always very thin (hence "membrane") and because H+ ions are in effect protons.