Nanostructured and porous antimony-doped tin oxide as electrode material for the heat-to-electricity energy conversion in thermo-electrochemical cells

Thermo-electrochemical cells (or thermogalvanic cells or thermocells, TECs) have gained attention as devices able to convert low temperature heat into electricity. Within TECs, Pt is one of the most employed electrodes, since it exhibits a fast transfer of electrons with the redox couple in the electrolyte. However, its high price represents a serious drawback. Here, we analyze the use of nanostructured and porous antimony-doped tin oxide (Sb:SnO₂) as electrode material. Electrodes of different thickness (320, 550 and 1550 nm) were fabricated by spin coating to study the effect of the electrode area in contact with the electrolyte. F:SnO₂ (FTO) glass was used as a substrate and the typical 0.4 M potassium ferro/ferricyanide aqueous solution served as electrolyte. An impedance spectroscopy analysis under operating conditions (10 K temperature difference) showed that the Sb:SnO₂ electrodes exhibit the same excellent kinetics as Pt for all the different thickness. On the other hand, the power output density was thickness independent, since the temperature coefficients and the series and mass-transport resistances were similar, leading to no performance improvements when the electrode area in contact with the electrolyte was significantly increased. Finally, the Carnot-related efficiencies estimated for the Sb:SnO₂ cells were in the same order of magnitude as for Pt electrodes. These results open the possibility to use Sb:SnO₂ as a suitable electrode in TECs at low cost.