Fabrication of robust and versatile ionic thermoelectric devices of natural clay minerals

Abstract

Due to advantages like high Seebeck coefficients, simple fabrication techniques, and use of abundant elements, ionic thermoelectric (i-TE) devices are emerging to be an ideal tool for harvesting low-grade waste heat. However, high dependence on humidity and poor thermal stability of organic polymers/polyelectrolytes/ionic liquids are restricting the utility area of i-TE devices. To expand the horizon of applicability, here, thermally and chemically robust natural clay minerals are explored for fabricating i-TE devices. Devices prepared with exfoliated layers of clay showed high Seebeck coefficients (6 ± 0.8 mV/K), which is significantly improved (up to 140 %) upon functionalization with the –SO3H groups (14.4 ± 0.4 mV/K). i-TE devices of clay exhibit unique advantages like thermal robustness and water-induced damage healing ability. These devices did not show any sign of deterioration even after exposure to 300 °C. Along with waste heat, clay-i-TE devices can also convert abundant sunlight energy into electricity. Upon being coated with polyvinyl alcohol (PVA), borax, and LiCl-based hydrogel the performance of the i-TE device at low-humidity conditions is drastically improved. The possibility of practical utility of clay-based i-TE devices was demonstrated in areas like fire alarms, touch sensors and electricity generation from hot water steam.