Thermoelectric Properties of Ultralong Silver Telluride Hollow Nanofibers

Ultralong Ag_<i>x</i>Te_<i>y</i> 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_<i>x</i>Te_<i>y</i> nanofibers were synthesized at low Ag⁺ concentrations, Ag-rich nodular Ag_<i>x</i>Te_<i>y</i> nanofibers were obtained at high Ag⁺ concentrations. The Te-rich nanofibers consist of coexisting Te and Ag₇Te₄ phases, and the Ag-rich fibers consist of coexisting Ag and Ag₂Te 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, <i>S</i>, but reduces the electrical conductivity, σ, due to the energy filter effect. The Ag₇Te₄/Te system was not competitive with the Ag₂Te/Ag system due to its high barrier height where the increase in <i>S</i> could not overcome the severely diminished electrical conductivity. The highest power factor was found in the Ag₂Te/Ag-rich nanofibers with an energy barrier height of 0.054 eV

Galvanically Displaced Ultralong Pb_<i>x</i>Se_<i>y</i>Ni_<i>z</i> Hollow Nanofibers with High Thermopower

A cost-effective process that combines electrospinning and a galvanic displacement reaction was utilized to synthesize ultralong hollow Pb_<i>x</i>Se_<i>y</i>Ni_<i>z</i> nanofibers with controlled dimensions, morphology, composition, and crystal structure. Ni nanofibers were electrospun with an average diameter of 150 nm and were used as the sacrificial material for the galvanic displacement reaction. The composition and morphology of the Pb_<i>x</i>Se_<i>y</i>Ni_<i>z</i> nanofibers were controlled during the reaction by tuning the concentration of HSeO₂⁺ in the electrolytes. Hollow Pb_<i>x</i>Se_<i>y</i>Ni_<i>z</i> nanofibers with smooth surfaces were obtained from the low-concentration HSeO₂⁺ solution (i.e., 0.01 and 0.05 mM), but the hollow nanofibers synthesized from the high-concentration HSeO₂⁺ solution (i.e., 1 mM) have rough outer surfaces with nanocrystal protrusions. The Pb content of the nanofibers’ composition was varied from 3 to 42% by adjusting the HSeO₂⁺ concentration. The thermoelectric properties of the nanofiber mats were characterized, and the highest Seebeck coefficient of approximately 449 μV/K at 300 K was found for the Pb₃₇Se₅₉Ni₄ nanofiber mat