Alkali-metal thermal to electric converter
An alkali-metal thermal-to-electric converter (AMTEC, originally called the sodium heat engine or SHE) is a thermally regenerative electrochemical device for the direct conversion of heat to electrical energy. It is characterized by high potential efficiencies and no moving parts except for the working fluid, which make it a candidate for space power applications.
Source: Wikipedia — Alkali-metal thermal to electric converter (CC BY-SA 4.0)