FUEL CELLS - Desktop Study

1. BASIC PRINCIPLES OF FUEL CELLS

 Fuel cells combine hydrogen and oxygen gas (or air) and convert the chemical energy of the mixture into electricity directly without an intermediate combustion step.

In principle, a fuel cell operates like a battery. Unlike a battery, a fuel cell does not undergo a material change. Consequently it does not run down or require recharging; the system can produce power continuously, as long as the fuel supply is maintained.

A fuel cell consists of 2 electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, heat and water.

Hydrogen is fed into the “anode” of the fuel cell. Oxygen (or air) enters the fuel cell through the “cathode”. Encouraged by a catalyst, the hydrogen atom split into a proton and an electron, which take different path to the cathode. The proton passes through the electrolyte, the electron create a separate current that can be utilised before they return to the cathode, to be reunited with hydrogen and oxygen in a molecule of water. Thus the fuel cell operation, essentially, is a reversal of the process of electrolysis.

The electrical current produced is proportional to the size (area) of the electrodes. The voltage is limited electrochemically to about 1.23 Volts per electrode pair, or cell. These cells can then be “stacked” until the desired power/voltage level is reached.

Because a fuel cell transforms fuel directly to electricity without intermediate conversion to heat, less waste heat is produced and very high conversion efficiencies, in the range from 40 to 60 percent, can be achieved. Additionally the constant temperature operation of a fuel cell allows the heat liberated by the electrochemical reaction to be used for space or water heating. When a fuel cell is used in this co-generation mode, producing both power and heat, it can achieve overall efficiencies as high as 80 percent

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Fig 1: Fuel cell – principle of operation

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