Alkaline
Alkaline Fuel Cells (AFCs) were the first type of fuel cell to be widely used for manned space applications. AFCs contain a potassium hydroxide (KOH) solution as the electrolyte. AFCs operate at temperatures between 100°C and 250°C (211°F and 482°F). Higher temperature AFCs use a concentrated (85wt%) KOH solution while lower temperature AFCs use a more diluteKOH solution (35-50wt%). The electrolyte is contained in and/or supported by a matrix (usually asbestos) which wicks the electrolyte over the entire surface of the electrodes. A wide range of electro-catalysts can be used in the electrodes (e.g., Ni, Ag, spinels, metal oxides, and noble metals). The fuel supplied to an AFC must be pure hydrogen. Carbon monoxide (CO) poisons an AFC and carbon dioxide (CO2) reacts with the electrolyte to form potassium carbonate (K2CO3). Even the small amount of CO2 in the atmosphere (about 370 ppm) must be accounted for operation of an AFC (Hirschenhofer et al., 1998).