Extensive Analysis on the Thermoelectric Properties of Aqueous Zn-Doped Nickel Ferrite Nanofluids for Magnetically Tuned Thermoelectric Applications.

Because of the ever-increasing consumption of energy, higher-efficiency thermoelectric materials are in more demand. In this regard, initially, ZnNiFeO nanoparticles were synthesized using a co-precipitation technique and investigated using Rietveld refinement and Brunauer-Emmett-Teller (BET) analyses. Then, they were dispersed in water to obtain stable 1 vol % of aqueous ZnNiFeO nanofluids and their viscous, electrical, thermal, and thermoelectric properties were analyzed in the absence and presence of a magnetic field. The Rietveld refinement revealed the formation of single phase spinel ferrite structures and cationic distribution of ZnNiFeO nanoparticles, whereas BET analysis revealed the surface area of the nanoparticles. The viscosity studies proved the pseudo-plastic shear thinning behavior and dipole-dipole interactions of ZnNiFeO nanofluids. The electrical conductivity, thermal conductivity, and Seebeck coefficient studies revealed that the maximum enhancement was observed for the ZnNiFeO nanofluid, which was attributed to the enhanced electrical double layer formation and Brownian motion of nanoparticles in the nanofluid. The enhancement in the properties of synthesized nanofluids in the presence of a magnetic field was attributed to the formation of chain-like structures, which was substantiated through the magneto-viscosity studies. The thermoelectric energy conversion efficiency of ZnNiFeO nanofluids was calculated which showed that the maximum enhancement of 27% was observed in the ZnNiFeO nanofluid at 770 G. The observed results proved that the synthesized nanofluids are magnetically tunable thermoelectric materials which are suitable for waste heat energy harvesting applications.