Electro-Chem-Technic :: Alkali Electrolyte Fuel Cells

Alkali Electrolyte Fuel Cells:

The electrolyte in an "alkali fuel cell" is usually KOH (potassium hydroxide) solution. The important feature of an alkali is that there is an excess of OH- ions, and these play a key role in the reactions inside the cell.

In order to understand how an electric current is produced, it is necessary to consider the reactions that take place at each electrode.

At the anode, hydrogen gas reacts with the OH- ions, producing water, and releasing electrons. The reaction is:-

The electrons go round the electrical circuit attached to the fuel cell, and reach the cathode. Here they react with the oxygen, and water, producing more OH- ions to replenish those used at the anode.

The OH- ions move through the electrolyte, and the electrons move round the circuit. The complementary movement of ions and electrons is shown in the diagram below.

Note two important points:-

1) Water is produced at the anode twice as fast as it is used up at the cathode. (In the solid polymer cell water is made at the cathode.)

2) The cathode is the electricaly positive terminal, the one that the electrons flow towards. Some people find this confusing, since they are quite wrongly taught that the cathode is the negative terminal for everything. It is not! The cathode is also the correct name for the positive terminal of any primary cell. (See the Oxford English Dictionary!)