Nanostructuring and oxygen-vacancy tuning to repress thermal transport and activate thermoelectric properties of green-synthesized ZnO

Abstract

We introduce eco-friendly synthesized ZnO nanoparticles by using orange peel extract for thermoelectric applications. Orange peel extract plays a crucial role as a reducing and surface-stabilizing agent in the synthesis process. It significantly affects the microstructure and lattice defects governing transport properties and thermoelectric performance of polycrystalline ZnO. A comparison of the structural and thermoelectric properties between the green-synthesized ZnO (ZnO OPE) and commercial ZnO (ZnO com) is conducted. The outcomes indicate that the ZnO OPE sample exhibits a 3.5-time higher electrical conductivity than the commercial ZnO at 1073 K, which is thermally activated at more than 673 K by oxygen vacancies. Moreover, the highly porous nanostructure of the ZnO OPE sample substantially reduces thermal conductivity from 14.5 W/mK to 5.5 W/mK with increasing temperature from 300 to 1073 K. The combination of nanostructure and defect modification paves the way for thermoelectric ZnO-based materials synthesized using environmentally friendly processes.