Alkaline fuel cell

[[Image:alkalinecell.svg|thumb|270px|Diagram of an Alkaline Fuel Cell:<br />

1. Hydrogen <br />

2. Electron flow <br />

3. Load <br />

4. Oxygen <br />

5. Cathode <br />

6. Electrolyte <br />

7. Anode <br />

8. Water <br />

9. Hydroxide Ions]]

The alkaline fuel cell (AFC), also known as the Bacon fuel cell after its British inventor, Francis Thomas Bacon, is one of the most developed fuel cell technologies. Alkaline fuel cells consume hydrogen and pure oxygen, to produce potable water, heat, and electricity. They are among the most efficient fuel cells, having the potential to reach 70%.

NASA has used alkaline fuel cells since the mid-1960s, in the Apollo-series missions and on the Space Shuttle.

Half Reactions

The fuel cell produces power through a redox reaction between hydrogen and oxygen. At the anode, hydrogen is oxidized according to the reaction:

<math>\mathrm{H}_2 + \mathrm{2OH}^- \longrightarrow \mathrm{2H}_2\mathrm{O} + \mathrm{2e}^-</math>

producing water and releasing electrons. The electrons flow through an external circuit and return to the cathode, reducing oxygen in the reaction:

<math>\mathrm{O}_2 + \mathrm{2H}_2\mathrm{O} + \mathrm{4e}^- \longrightarrow \mathrm{4OH}^-</math>

producing hydroxide ions. The net reaction consumes one oxygen molecule and two hydrogen molecules in the production of two water molecules. Electricity and heat are formed as by-products of this reaction.

Electrolyte

The two electrodes are separated by a porous matrix saturated with an aqueous alkaline solution, such as potassium hydroxide (KOH). Aqueous alkaline solutions do not reject carbon dioxide (CO₂) so the fuel cell can become "poisoned" through the conversion of KOH to potassium carbonate (K₂CO₃). Because of this, alkaline fuel cells typically operate on pure oxygen, or at least purified air and would incorporate a 'scrubber' into the design to clean out as much of the carbon dioxide as is possible.