Converting natural diatomite into nanoporous silicon for eco-friendly thermoelectric energy conversion

Abstract Thermoelectric generators are one type of clean energy technologies, capable of converting heat to electricity with no pollution discharge. However, the component elements of the traditional thermoelectric materials are usually rare or toxic. Silicon is non-toxic and abundant, but has too high a thermal conductivity for generation of a temperature gap. Herein, nanocrystallization and nanoporosification are concurrently realized via a thermite reaction based on naturally abundant and eco-friendly diatomite. The thermal conductivities of the nanoporous Si nanobulk are depressed by 2 orders of magnitude compared to that of single-crystal Si, due to significantly enhanced phonon scattering, as the size of the nanograins (~40 nm) and nanopores (~100 nm) are close to the mean free path of the majority phonons. The maximum output power density is 1.14 and 1.81 Wm−2 for n and p-Si single legs under a temperature difference of 40 K, suggesting great potential for use in eco-friendly devices that can harvest electricity from waste heat.