(558a) Thermoelectric Properties of Ultra-Long PbSe Hollow Nanofibers

Lead selenide (PbSe), a sister material of lead telluride (PbTe), has been less focused on for thermoelectric (TE) applications due to its smaller band gap energy and an expected higher thermal conductivity.   Recently, however, an additional notion has been placed to the material, since a TE figure of merit (ZT) up to 1.2 at 850 K was experimentally achieved, approaching the theoretical value of 1.6.  In addition, significant progress has been made to enhance the Seebeck coefficient while diminishing the thermal conductivity by using low dimensional PbSe.  However, even though a thermal power 3 times greater than that of bulk in PbSe quantum dot superlattices has been reported, only a low power factor was extracted attributing to its high electrical resistivity.  One-dimensional (1-D) PbSe, on the other hand, shows a better electrical conductivity with a significant decreased thermal conductivity, but the prevailing difficulty and high cost in a device fabrication hinders its application in a real TE apparatus. Therefore, low dimensional PbSe with superior TE performance is highly demanded, through a cost-effective fabrication process.

While several techniques exist for creating 1-D PbSe nanostructures, electrospinning (ES) has emerged as the most versatile, scalable and cost-effective method to synthesize ultra-long nanofibers (NFs) with controlled diameter and composition. Although various NFs have been synthesized using this technique, limited work has been reported on chalcogenide NFs synthesis due to the incompatibility of the precursors. Therefore, synthesis of PbSe was conducted through ES with the addition of a galvanic displacement reaction (GDR); this is a spontaneous electrochemical process driven by the difference in materials’ redox potentials. In this approach, ES is exploited to fabricate ultra-long sacrificial NFs with controlled dimensions, morphology and crystal structures, providing a large materials’ data base to tune electrode potentials thereby imparting control over the composition and shape of the nanostructures evolved during GDR. Synthesized samples are designed to be in a bulk scale for easy device fabrication, but reserve the superior properties form nanoscale materials.

In this work, we demonstrated high scalability and cost-effective nanofabrication to synthesize ultra-long hollow PbSe nanofibers by combining ES and a GDR. Control over the diameter, wall-thickness, morphology, composition and crystallinity of the NFs was achieved by tuning the shape and dimension of the sacrificial materials as well as GDR conditions.  Temperature dependent electrical resistivity and Seebeck coefficient measurement were performed for the TE properties characterization.  Preliminary result showed an excellent Seebeck coefficient of 525 µV/K and a power factor of 0.43 µW/K²m at 26 ^oC in the PbSe hollow NF mat.