This fuel cell is a cutaway version of the electric-power generating device used on the two-astronaut Gemini spacecraft during ten missions in 1965-66. A fuel cell is like a battery, in that it uses a chemical reaction to create an electrical current. Unlike a battery, a fuel cell will continue to generate a current as long as the reactants are supplied. The Gemini fuel cell used liquid oxygen and liquid hydrogen to generate electricity, with water as a byproduct. Oxygen and hydrogen molecules reacted and combined across a "proton exchange membrane," a thin permeable polymer sheet coated with a platinum catalyst.The Gemini program pioneered the use of fuel cells in space, and this technology was subsequently used in the Apollo Service Module and the Space Shuttle Orbiter. General Electric, the manufacturer of Gemini fuel cells, gave this artifact to the Smithsonian in 1966.