electrolyte and fuel. By the 1990s fuel cells had been built into systemsincorporating a means for the storage and controlled supply of fuel and oxidantand for the removal of heat and reaction products. For possible future spaceflights of long duration, solar or nuclear generators are considered more suitablethan fuel cells, though regenerative fuel cells may be used to supplement thesedevices. Hydrogen-oxygen fuel cells also have been used to power forklifts andsmall automotive vehicles on an experimental basis.Various exploratory attempts have been made to introduce fuel cells intocommercial use, but so far none has been particularly successful. Fuel cells thatoperate on methanol, however, have been employed on a limited scale topower television repeater stations and navigation beacons.High-temperature solid-oxide fuel cell (SOFC) systems show great promisefor the economical production of electricity and heat in a variety ofcommercial, residential, and industrial applications. Relying on a readilyavailable source of heat, such as natural gas, SOFC technology is based on theability of a stable component, such as zirconium oxide, to operate as a solidelectrolyte at high temperatures. ELECTROLYSIS In a battery-driven circuit, the flow of electric current is produced byspontaneous chemical changes that occur at each battery terminal. In abattery, stored chemical energy is converted to electrical energy.In electrolysis the process is reversed. By forcing an electric currentthrough some substances, it is possible to change electrical energy into storedchemical energy. The process of electrolysis causes chemical reactions that donot occur spontaneously. For example, when common table salt, or sodiumchloride (NaCl), is heated to 1,486o F (808o C), the solid turns to a stable meltconsisting of sodium ions (Na+) and chloride ions (Cl-). If inert electrodes areimmersed in the melt and an electric current is forced through the molten saltby a suf...
