Thermoelectric Properties of Ultralong Silver Telluride Hollow Nanofibers

Abstract

Ultra-long Ag x Te y nanofibers were synthesized for the first time by galvanically displacing electrospun Ni nanofibers. Control over the nanofiber morphology, composition and crystal structure was obtained by tuning the Ag + concentrations in the electrolytes. While Te-rich branched p-type Ag x Te y nanofibers were synthesized at low Ag + concentrations, Ag-rich nodular Ag x Te y nanofibers were obtained at high Ag + concentrations. The Te-rich nanofibers consist of coexisting Te and Ag 7 Te 4 phases, and the Ag-rich fibers consist of coexisting Ag and Ag 2 Te phases. The energy barrier height at the phase interface is found to be a key factor affecting the thermoelectric power factor of the fibers. A high barrier height increases the Seebeck coefficient, S, but reduces the electrical conductivity, σ, due to the energy filter effect. The Ag 7 Te 4 /Te system was not competitive with Ag 2 Te/Ag system due to its high barrier height where the increase in S could not overcome the severely diminished electrical conductivity. The highest power factor was found in the Ag-rich nanofibers with an energy barrier height of 0.054 eV. INTRODUCTIONThe rising cost of compliance to laws and regulations (from the Clean Air Act to Geologic Sequestration) for consuming non-renewable energy resources is the key driver to improve the efficiency of environmentally-friendly and renewable energy generation. 1 Thermoelectric materials offer simple, silent and reliable solid-state energy conversion devices due to their unique ability to directly convert heat into electricity and viceversa without moving parts or bulk fluids. The efficiency of a thermoelectric device can be determined by the thermoelectric figure-of-merit (ZT), given by ܼܶ = ܵ ଶ ߪܶ/ߢ. Here S, σ, κ, T, and S 2 σ are the Seebeck coefficient, electrical conductivity, thermal conductivity, temperature, and power factor, respectively. Nonetheless, the interrelationships of these key parameters in a bulk material tend to offset one another making it difficult to improve ZT. 2 Recent research in low-dimensional, especially one-dimensional (1-D) thermoelectric nanostructures, has invigorated the field by identifying quantum confinement, the energy filtering effect, and stronger phonon scattering effects to enhance S 2 σ and reduce κ. 3-5 Quantum confinement shifts the Fermi level away from the conduction band, creating a greater energy difference between them thereby improving the power factor. 6 Energy filtering enhances the average carrier energy by filtering out low energy carriers at grain boundaries or interfaces, thus increasing the Seebeck coefficient and optimizing the power factor. 7 Stronger phonon scattering at the grain boundaries and interfaces is anticipated in 1-D nanostructures due to their larger surface-to-volume ratio, which can significantly decrease the thermal conductivity. Among 1-D thermoelectric materials, nanotubes benefit from their unique wall thickness, which provides an extra de-

Development of Perovskite-Type Materials for Thermoelectric Application

“…However, normally there is no clear operation temperature boundary for each type of TE materials, for instance, rare earth chalcogenides, group III–V compounds, oxide perovskites materials, borides and metal oxides can be applied in a vast range of temperature depending on specific compounds [10,17,36,38,39,40]. The inorganic materials are the most well-studied TE materials [3,7,10,11,12,36,41]. We have studied the thermoelectric properties of PbTe films [20] and silver telluride nanofibers [41].…”

“…The inorganic materials are the most well-studied TE materials [3,7,10,11,12,36,41]. We have studied the thermoelectric properties of PbTe films [20] and silver telluride nanofibers [41]. Additionally, Te nanostructures including nanowire [42], nanotree [42], and nanorice [43] were synthesized, which can be used to be embedded into other TE materials as nanocomposite [44,45,46] or converted to metal tellurides through cation exchange reaction [47,48].…”

Metal Telluride Nanomaterials: Facile Synthesis, Properties and Applications for Third Generation Devices.

“…Similarly the various metal telluride such as ZnTe, PbTe, Ag 2 Te,, Bi 2 Te 3 , Bi 0.4 Sb 1.6 Te 3 (BiSbTe), nanoparticles with exceptional enhanced thermoelectrical properties has been synthesized for the use in thermoelectric device applications. Copper telluride nanowires/polyvinylidene fluoride were used as a building block to synthesize flexible thin films which exhibit room temperature electrical conductivity and Seebeck coefficient of 2490 S/cm and 9.6 μv/K respectively, ensuing in a power factor of 23 μW/(mK 2 ) at room temperature.…”

Synthesis and Thermoelectric Characterization of Lead Telluride Hollow Nanofibers

“…Therefore, synthesis of a few millimeter chalcogenide nanofibers has been realized by combining electrospinning with an additional process called the galvanic displacement reaction (Xiao et al, 2007b ; Chang et al, 2010a , b , 2014 ; Hangarter et al, 2010 ; Jung et al, 2010 , 2012 ; Park et al, 2010 , 2013 ; Rheem et al, 2010 ; Suh et al, 2012 , 2013 ; Elazem et al, 2013 ; Jeong et al, 2013 ; Liu et al, 2013 ; Wu et al, 2014 , 2015 ; Zhang et al, 2014 ), by which the electrospun nanofibers can be converted to desired hollow metal chalcogenides spontaneously. Several hollow nanofibers of chalcogens and metal chalcogenides [e.g., Te (Lee et al, 2011 ; Jeong et al, 2013 ), Ag 2 Te (Park et al, 2015 ; Zhang et al, 2015 ), and Pb x Se y Ni z (Zhang et al, 2014 )] have been successfully synthesized by this method in our group.…”