Fuel cells:
These are galvanic cells in which the energy of combustion of fuels is directly converted into electrical energy. Commonly used fuels are hydrogen, methanol etc.
A fuel cell can be defined as an electrochemical cell that generates electrical energy from fuel via an electrochemical reaction. These cells require a continuous input of fuel and an oxidizing agent in order to sustain the reactions that generate the electricity.
Therefore, these cells can constantly generate electricity until the supply of fuel and oxygen is cut off.
The half cell reactions in hydrogen - oxygen fuel cell are given below.
Oxidation at anode:
Hydrogen gas and hydroxide ions are oxidized to water.
2H₂ (g) + 4OH⁻ (aq) → 4H₂O (l) + 4e⁻
Reduction at cathode:
Oxygen gas and water molecules are reduced to hydroxide ions.
O₂ (g) + 2H₂O (l) + 4e⁻ → 4OH⁻ (aq)
This electrochemical reaction, however, has a slow reaction rate. A catalyst, such as platinum or palladium, is used to solve this issue.
To increase the effective surface area, the catalyst is finely divided before being incorporated into the electrodes.
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