Generating current from a fuel
A fuel cell is an electrochemical cell in which a fuel is oxidised at one electrode while oxygen is reduced at the other. Separating these processes causes electrons to travel through the external circuit, producing an electric current.
The fuel supplies electrons as it undergoes oxidation. Oxygen accepts electrons at the other electrode. Ions move through the electrolyte to complete the internal circuit.
Fuel electrode
The fuel is oxidised and releases electrons.
External circuit
Electrons move through the external circuit and can perform electrical work.
Oxygen electrode
Oxygen is reduced by accepting electrons.
Continuous operation
Unlike a conventional rechargeable cell, a fuel cell does not store all of its reactants within the cell. It can continue operating while fresh fuel and oxygen are supplied and products are removed.
A hydrogen fuel cell can maintain a comparatively constant voltage while fresh and continue to be supplied, because their concentrations are maintained. In an ordinary cell, the voltage decreases as reactants are consumed.
For this reason, a fuel cell does not need to be electrically recharged in the way a secondary cell does. Its operation depends instead on maintaining the external supply of reactants.
Exam Tip: If asked why a fuel cell does not need recharging, state that fuel and oxygen are supplied continuously. Do not say that the cell recharges itself.