(645e) Fabrication of Bulk Thermoelectrics from Large-Scale Assemblies of Zn3P2 and ZnO Nanowires

Thermoelectrics, solid-state heat engines, are both useful for the recovery of waste heat or the generation of renewable energy. The lack of any moving parts, portability, very long operational lifetimes, and minimal maintenance requirements make them very attractive for these applications. Current state-of-the-art thermoelectric modules not only exhibit low efficiencies, but are also composed of toxic and rare-earth elements. The lack of a pathway for precisely and independently tuning the thermal and electrical transport through materials employed in the fabrication of thermoelectrics is the primary reason for their low efficiencies. Recent theoretical and experimental studies have indicated that nanostructuring of materials serves as a route for independently tuning the thermal and electrical transport through them, and enhance their heat-to-electricity conversion efficiencies. Of all the forms of nanomaterials, nanowires hold the most promise for the fabrication of efficient thermoelectric modules. The two different dimensions of the nanowires, namely the diameters and the lengths, offer a convenient path for independently tuning the electrical and thermal transport through them. As thermoelectrics is a bulk application, large-scale deployment and use of nanowire-based thermoelectric modules requires strategies for the synthesis and assembly of nanowire powders on an industrial scale. In this context, this work describes strategies for the bulk production of Zn₃P₂ nanowire powders and their in-situ functionalization with conjugated organic molecules (1,4-benzenedithiol (BDT) and 4-aminothiophenol (4-ATP)), together with the strategies useful for assembling them in an interface-engineered manner. The thermoelectric performance of these inorganic-organic hybrids will be discussed. Also, the optimization of the microstructure and composition of the nanowire assemblies for realizing a 500 fold increase in the thermoelectric performance to a ZT value of 0.23 will be discussed. Optimal doping of ZnO nanowire assemblies for obtaining a ZT value of 0.6 will also be discussed.