Chemical cells and fuel cells

Chemical cells produce a voltage from electrochemical reactions between different metals and an electrolyte.

• •The voltage produced by a cell depends on the identity of the metal electrodes and the type and concentration of the electrolyte.
• •The greater the difference in reactivity between the two metals used as electrodes, the higher the voltage produced by the cell.
• •In non-rechargeable cells, the chemical reactions stop when one of the reactants is completely used up.
• •In rechargeable cells, the chemical reactions can be reversed because an external electrical current is applied.

Hydrogen fuel cells use the electrochemical oxidation of hydrogen to generate electricity, releasing only water as a byproduct.

• •In a hydrogen fuel cell, hydrogen is oxidised electrochemically to produce water, with an overall equation of 2H₂ + O₂ → 2H₂O.
• •At the negative electrode (anode), hydrogen molecules lose electrons to form hydrogen ions: 2H₂ → 4H⁺ + 4e⁻.
• •At the positive electrode (cathode), oxygen gains electrons and reacts with hydrogen ions to form water: O₂ + 4H⁺ + 4e⁻ → 2H₂O.
• •The major advantage of hydrogen fuel cells is that they produce no greenhouse gases or pollutants during operation, only water.
• •Unlike rechargeable batteries, fuel cells do not lose charge capacity over time and will run continuously as long as fuel and oxygen are supplied.