Alkaline fuel cells were one of the first modern fuel cells to be developed at the beginning of the 1960's. They were the first type widely used in the US space programme to provide on-board electric power for the Apollo space shuttle. The electrolyte is concentrated (85 wt%) potassium hydroxide (KOH) in fuel cells operating at high temperatures (above 250°C), and less concentrated (35-50 wt%) KOH for lower temperature operation. Recently developed systems can run at temperatures below 100°C. Oxygen reduction in alkaline environments is much faster than in acidic conditions, as in the PEMFC. Thus, it is possible to use a wide range of cathode electrocatalysts, e.g., Ni, Ag, metal oxides, spinels, in addition to noble metals. Inexpensive catalyst materials such as Raney Nickel or Raney Silver were investigated in the early stages of the AFC's history. The electrode reactions are as shown below:

Anode oxidation of hydrogen: 

H₂ + 2OH^- 2H₂O + 2e^-

Cathode reduction of oxygen:

½O₂ + H₂O + 2e^- 2OH^-

Total AFC reaction:

H₂ + ½O₂ H₂O

Instead of protons as in PAFC and PEMFC, hydroxyl ions (OH^-) are the conductive ions in AFC. The fuel supply is limited to very pure hydrogen and oxygen. Carbon monoxide is a catalyst poison, and carbon dioxide will react with the electrolyte (KOH) to form K2CO3 (solid salts), thus altering the electrolyte. Even small amounts of CO2 in the air are damaging to the alkaline cell. The carbonates are formed according to the following reaction equation:

CO₂ + 2OH^- (CO₃)^2- + H₂O

In the first space AFC systems, the KOH electrolyte was retained in a matrix. Further development led to a circulating electrolyte, which provides a better barrier against gas leakage, increases the lifetime of the electrolyte and the liquid can also be used to cool the stack. Desirable attributes of the AFC include its excellent performance with hydrogen and oxygen due to its active cathode kinetics. In space applications efficiencies up to 60% have been reached. This is much higher than has been possible with other fuel cell types.

Recently the interest in AFC has dropped considerably. Practical problems with cost-effective removal of CO2 in the cathode air feed has limited the use of AFC systems to special applications like spacecraft and submarines. A British company, Zetek, focussed on AFC in automobile applications for some time, see pictures below. In 2002 the activity was stopped due to lack of funding.

Zevco AFC public vehicle.

Zevco AFC London Taxi.

Kordesch motorbike.

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