Fuel cell types

The alkaline fuel cell

Properties and structure

The alkaline fuel cell (English Alkaline Fuel Cell (AFC) is a low temperature fuel cell. It works in the temperature range of approx. $20$ until $90\text{° C}$ and achieves efficiencies between $60$ until $70\text{\%}$. The oxygen used as the oxidizing agent must also be very pure.

Potash lye (usually 30%) serves as the electrolyte in these cells. For example, platinum or Raney nickel is used as a catalyst in the graphite gas diffusion electrodes.

Reaction

$$\begin{array}{cccc}\hfill 2{\text{H}}_2+4\text{O}{\text{H}}^{-}& \to & 4{\text{H}}_2\text{O}+4{\text{e}}^{-}\hfill & \text{Anode reaction}\hfill \\ \hfill {\text{O}}_2+2{\text{H}}_2\text{O}+4{\text{e}}^{-}& \to & 4\text{O}{\text{H}}^{-}\hfill & \text{Cathodic reaction}\hfill \\ \hfill 2{\text{H}}_2+{\text{O}}_2& \to & 2{\text{H}}_2\text{O}\hfill & \text{Overall response}\hfill \end{array}$$

Advantages and disadvantages

Advantages:

• good efficiency
• Use of inexpensive catalysts

Disadvantage:

• Intolerance to carbon dioxide (CO₂), since the potassium hydroxide crystallizes out of the potassium hydroxide otherwise to form insoluble carbonate. For this reason, the AFC can only be used with highly pure, i.e. CO₂-free fuels are operated, i.e. pure water and oxygen. Because of its CO₂Content cannot be used.

Applications

Military (e.g. submarine drives), on-board power supply for manned space shuttles