Processability of Thermoelectric Ultrafine Fibers via Electrospinning for Wearable Electronics

Abstract

Polymer-based thermoelectric generators hold great appeal in the realm of wearable electronics as they enable the utilization of body heat for power generation. Fibers produced from conducting polymers for use in thermoelectric generators have high porosity and good flexibility, providing comfort-based performance advantages over thin films for wearable electronics. Some fiber processing techniques have been explored to produce textile-based thermoelectric generators; however, they fail to approach the conductivities of polymeric thin films. Ultrafine fibers solution processed through electrospinning yield fiber diameters on the nanoscale, allowing for high surface area to volume ratios and thus low thermal conductivity; however, a number of processing challenges in electrospinning conducting polymers limit the success of preparing high performing thermoelectric textiles. In this work, the specific processing challenges inherent to electrospinning conducting polymers are addressed for both n- and p-type materials. For the p-type polymer, 63 wt % PEDOT:PSS fibers are fabricated through solution formulation improvements yielding a conductivity of 3 S/cm and a power factor of 0.1 μW/mK2. The first of their kind n-type poly­(NiETT)/PVA electrospun fibers were created yielding a conductivity of 0.11 S/cm and a power factor of 0.0036 μW/mK2. These nonwoven ultrafine fiber mats show progress toward achieving textile-based thermoelectric materials with equivalent performance of comparable polymeric thin films. This work shows the feasibility of creating ultrafine fibers for use in thermoelectric generators through electrospinning including the first demonstration of poly­(NiETT)/PVA fibers.

The Potential of Electrospinning to Enable the Realization of Energy-Autonomous Wearable Sensing Systems

“…In addition to their flexibility and stretchability, materials produced through the electrospinning technique possess naturally high surface area and porosity, leading to significantly reduced thermal conductivity and ultimately higher zT values. 173 TEG devices typically rely on p-and n-type material-based systems to generate high power in real-world applications. However, CNT stands out for its ability to convert carrier type compared to other materials.…”

“…The dimensionless figure of merit ( zT ) is used to evaluate the thermoelectric potential of thermoelectric materials and can be calculated using eq z T = S 2 σ k T where, S is the Seebeck coefficient, σ is the electrical conductivity (depends on carrier charges, mobility, and concentration), and k and T are the thermal conductivity (combination of lattice and electron thermal conductivity) and absolute temperature, respectively . Popular thermoelectric materials such as bismuth telluride combined with metal alloys are often rigid, expensive, and nonbiocompatible. , Nozariasbmarz et al have provided a comprehensive review on wearable thermoelectric energy harvesters, providing evidence that nanostructured (Bi x Sb 1– x ) 2 Te 3 and Bi 2 Te 3– x Se x are mostly suitable for wearable TEG applications. The review also highlights the possibility of developing flexible TEGs using coating or printing techniques with either flexible or rigid interconnects for wearable applications .…”

“…However, since the long-term efficiency of such TEG devices decreases due to wearing and abrading, Ewaldz et al suggested that electrospinning is a better alternative. In addition to their flexibility and stretchability, materials produced through the electrospinning technique possess naturally high surface area and porosity, leading to significantly reduced thermal conductivity and ultimately higher zT values …”

“… 172 Popular thermoelectric materials such as bismuth telluride combined with metal alloys are often rigid, expensive, and nonbiocompatible. 14 , 173 Nozariasbmarz et al have provided a comprehensive review on wearable thermoelectric energy harvesters, providing evidence that nanostructured (Bi x Sb 1– x ) 2 Te 3 and Bi 2 Te 3– x Se x are mostly suitable for wearable TEG applications. The review also highlights the possibility of developing flexible TEGs using coating or printing techniques with either flexible or rigid interconnects for wearable applications.…”

“…In addition to their flexibility and stretchability, materials produced through the electrospinning technique possess naturally high surface area and porosity, leading to significantly reduced thermal conductivity and ultimately higher zT values. 173 …”