High Thermoelectric Power Generation below Room Temperature by TiS₂ Compact Pellet

The highly anisotropic single crystals of titanium disulfide (TiS 2 ) have an n-type semiconducting property with attractive thermoelectric (TE) performance above room temperature (RT). However, the TE properties and power generation below the RT of TiS 2 have not yet been reported. In this work, the TE performance of the TiS 2 powder compact in a pellet form was investigated in the temperature range of 233–323 K. Moreover, the power generation characteristics were measured under the temperature gradient of Δ T = 25 and 45 K either below or above RT. The electrical conductivity of the powder compact decreased by heating, while the Seebeck coefficient increased. Annealing the compact pellet was also performed and found to significantly enhance its TE performance. The resulting power factor recorded ∼540 μW/mK 2 at T = 233 K and stayed almost constant despite a temperature change. Similar trends were also observed in the charge carrier density and Hall mobility, with a slight decrease during heating. On the other hand, the measured in-plane thermal conductivity of a TiS 2 compact is 3.92 W/mK at T = 298 K and increased to 4.44 W/mK at T = 373 K. The resulting figure of merit, zT, was 0.041–0.048 at 298–373 K. The generated maximum power of a TiS 2 single leg module recorded 1.24 and 4.3 μW at Δ T = 25 and 45 K (cold side temperature T 1 and hot side temperature T 2 are both > RT), respectively, above RT. Surprisingly, the generated TE power below RT was found to be several times higher than the generated power above RT with recorded values of 10.2 and 26.5 μW at Δ T = 25 and 45 K ( T 1 and T 2 are both < RT), respectively. This remarkable result firmly indicates that comparatively costless TiS 2 compacts composed only of nontoxic elements should be useful to generate TE power in cold environments below RT utilizing the waste heat from a warm system.