Thermeoelectric generators (TEGs) make use of the Seebeck effect in a thermoelectric material to extract energy from a temperature gradient and recover otherwise wasted heat as electrical energy, and are among the front-running technologies to meet this challenge. TEGs are solid-state devices with no moving parts, and can be deployed at scales from wireless sensors, to vehicle exhausts, to industrial plants, and possibly even as primary renewable power sources. The large amount of global energy wasted as heat means that even modestly efficient TEGs could have a large impact on climate change -for example, a typical nuclear power plant loses ~60 % of its energy as waste heat, and a mere 5-10 % recovery would provide enough additional power for tens of thousands of homes.