In this work, we investigate the effects of Ni doping on the thermoelectric (TE) properties of Yb0.25Co4Sb12 sample. Yb0.25Co4-xNixSb12 (0 ≤ x ≤ 0.5) samples were prepared by mechanical alloying and subsequently consolidated by spark plasma sintering. The morphology of consolidated samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS). The thermoelectric properties of bulk samples were measured from room temperature to 800 K. The XRD analysis confirmed that, the successful formation of the Co4Sb12 skutterudite phase and Ni is substituted into Co site of the skutterudite crystal lattice. Moreover, the electrical resistivity decreased to 14.6 μΩm at 785 K for Yb0.25Co3.5Ni0.5Sb12 sample, due to increase of the electron concentration by Ni-addition. The absolute Seebeck coefficient reached the highest value of 223 μV/K at 592 K for Yb0.25Co3.7Ni0.3Sb12 sample, thus yielding a maximum value of power factor of 2.41 × 10-3 W/mK2 at 592 K. The highest dimensionless thermoelectric figure of merit value ZT of 0.49 at 692 K has been achieved for the Yb0.25Co3.7Ni0.3Sb12 sample, compared to ZT=0.06 for the Yb0.25Co4Sb12 sample at same temperature. This work indicates a strategy to improve the thermoelectric performance by Ni substitution of Co sites in the Yb0.25Co4Sb12 skutterudite through simultaneous improvement of its electrical conductivity, Seebeck coefficient and reduction of its thermal conductivity.
Thermally driven electrochemical cells (thermocells) are able to convert thermal gradient applied across redox electrolyte
into electricity. The performance of the thermocells heavily depends on the magnitude and integrity of the applied thermal
gradient. Herein, we study the iodide/triiodide (I–/I3
–) based 1-Ethyl-3-methyl-imidazolium Ethylsulfate ([EMIM][EtSO4])
solutions in a thermocell. In order to comprehend the role of fluidity of the electrolyte, we prepared set of solutions by
diluting [EMIM][EtSO4] with 0.002, 0.004, and 0.010 mol of Acetonitrile (ACN). We realized a significant improvement
in ionic conductivity (σ) and electrochemical Seebeck (Se) of diluted electrolytes as compared to base [EMIM][EtSO4]
owing to the solvent organization. However, the infra-red thermography indicated faster heat flow in ACN-diluted-[EMIM]
[EtSO4] as compared to the base [EMIM][EtSO4]. Therefore, the maximum power density of base [EMIM][EtSO4] (i.e.
118.5 µW.m-2) is 3 times higher than the ACN-diluted-[EMIM][EtSO4] (i.e. 36.1 µW.m-2) because of the lower thermal
conductivity. Hence this paper illustrates the compromise between the fast mass/flow transfer due to fluidity (of diluted
samples) and the low thermal conductivity (of the pure [EMIM][EtSO4]).