Catalysts All Around Us

Fuel Cells

Fuel cells are attracting a great deal of interest in the search for alternative energy supplies to fossil fuels, since they are very efficient and virtually pollution free. In a fuel cell a fuel gas such as hydrogen is combined with oxygen to produce electricity. This conversion happens at electrodes that are coated with catalysts. Unlike an ordinary battery which has a fixed life span, the fuel cell will continue to function for as long as the gases are supplied to it

Early 'alkali' fuel cells

One of the first fuel cells to be devised used porous graphite electrodes. The negative electrode was coated with nickel and the positive electrode coated with nickel and nickel(II) oxide. Both electrodes were in contact with a potassium hydroxide solution electrolyte so the cell became known as an ‘alkali fuel cell’.

Hydrogen supplied to the negative electrode was converted to water:

2H2 + 2OH-

4H2O + 4e

 

 

 

 

Oxygen supplied to the positive electrode was converted to hydroxide ions:

O2 + 2H2O + 4e

4OH-

 

 

 

 

The overall effect

Adding the two equations together we can see that the overall change is simply to produce water:

2H2 + O2

2H2O

 

Alkali fuel cells are still in use for providing on-board power in the space shuttle. These days, for safety reasons, the electrodes are made from an inert metal such as tantalum. The cathode is converted with platinum and gold and the anode with platinum.

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