Thermionic energy conversion (TEC) is the direct conversion of heat into electricity by the mechanism of thermionic emission, the spontaneous ejection of hot electrons from a surface. (FRONTIERSIN.ORG)The main components of these devices are for example boron nitride (BN), aluminum nitride (AlN), refractory metals and scandates. They are not so complicated and expensive like batteries components for sure. They can partially solve electricity generation issues where the resources are abundant but the plants are not operative or isolated. Lets see this great explanation from the Edison center themselves.
Links
http://large.stanford.edu/courses/2018/ph240/swifter2/
