A thermo-electric fan is a device that is powered by the difference in two temperatures. It works by using the two temperature extremes to create a bit of electricity that is capable of driving a tiny motor. Getting electricity from a hot and a cool point involves a device called a thermocouple, and it does provide enough electricity to replace a few batteries. The great thing about a thermo fan, aside from not needing any batteries, is that it can operate even when quite hot.
If a regular fan was sat on the top of a stove, it would be heated by the stove surface and the batteries would be damaged. This type of fan has a metal bottom and is quite resilient to heat. It might also be placed above a fireplace to help circulate air. The fan might cool bread or increase the passive flow of warm air.