were first widely used in the U.S. space program to produce electrical energy and water on-board a spacecraft, specifically in the Apollo missions to the Moon and later in the space shuttle program, specifically in the orbiter. AFC have also been used on vehicles like forklifts, as stationary power applications, backup power and in military applications. The electrolyte is a concentrated alkaline solution, usually potassium hydroxide due to its high conductivity, and operates on average bellow 100°C, though temperatures can range from below zero to 230°C. Anion exchange membranes have also been used as the electrolyte. 220 A wide range of electrocatalysts can be used at the anode and cathode due to the flexibility of the AFC design, although nickel, silver and platinum tend to be the most commonly used 219 . AFCs have a slightly different operating principle than other fuel cells because the electrolyte/membrane conducts hydroxyl anions (OH -) instead of H + cations 220 . The reactions that take place at each electrode are the following: