Abstract
Thermoelectric (TE) generators can directly convert exhaust waste heat into electricity in vehicles. However, the low conversion efficiency of TE generators is the main obstacle to their commercialization in automotive. Their efficiency mainly depends on the performance of the used materials which is quantified by the figure of merit (ZT value). In the present study, single- and co-doped calcium cobaltites(CCO) with rare-earth (Tb) and transition metals (Cu, Fe, Ni, Mn, Cr) were produced using sol-gel technique in order to improve their high temperature thermoelectric properties for heat recovery in exhaust manifold applications. By the combined effect of doping approach and the production technique used in this study, a remarkable decrease in the grain size of CCO was obtained, and thus its thermal conductivity dramatically decreased. Besides, thermopower values were improved significantly. The reduction in thermal conductivity and the increase in thermopower led to an enhancement in ZT value of CCO ceramics. Among all the co-doped samples, Tb-Cu co-doped CCO displayed the maximum ZT value of 0.116 at 873 K which is 2.5 times larger than that of pure CCO. The high thermal stability and the enhanced thermoelectric performance make Tb-Cu co-doped CCO material a potential candidate for heat recovery in automotive exhaust thermoelectric generators.
