Power factor improvement in a solid–liquid thermoelectric system formed by Sb:SnO2 in contact with a chromium complex solution

Abstract

Thermoelectric (TE) materials can convert heat into electricity. Good TE materials should have high power factors (PF) and low thermal conductivities. PF = S²σ is governed by the Seebeck coefficient S and the electrical conductivity σ. Most recent improvements in TE materials performance have been achieved by the reduction of the thermal conductivity, and strategies to improve the PF have been minor. Recently, an innovative concept to significantly increase the PF, based on the combination of a porous TE solid with an electrolyte, has been reported. Here, we make use of this new approach but using an electroactive salt (redox molecule) solution as electrolyte, rather than the non-electroactive electrolytes and ionic liquids previously employed. A system formed by a nanostructured and porous Sb:SnO₂ film in contact with Cr(III) acetylacetonate dissolved in 3-methoxypropionitrile was prepared. Using this electrolyte, an average PF enhancement of 3.4 times was achieved, due to an average decrease of 23.2% and 82.8% in the absolute value of the Seebeck coefficient and the electrical resistivity of the solid, respectively. An impedance spectroscopy analysis, after checking by scanning electron microscopy and energy-dispersive X-ray spectroscopy that no changes take place in the Sb:SnO₂ film due to the presence of electrolytes, revealed that the improvements come from the donation of electrons from the electrolyte to the solid, which increases its electrical conductivity and the usual drop in the Seebeck coefficient. The remarkable PF improvement obtained is among the highest reported and opens a new way of significantly enhancing this parameter.