Worm-Like PEDOT:Tos coated polypropylene fabrics via low-temperature interfacial polymerization for high-efficiency thermoelectric textile

Highlights

• A bioinspired worm-like thermoelectric fabric is fabricated by low-temperature interfacial polymerization.

• The Seebeck coefficient of the fabrics reaches as high as 16.15 μV K⁻¹ at 30 °C temperature difference.

• The electrical and mechanical performances of the as-prepared fabrics negligibly decreased after bending and ultrasonic test.

• The flexible coated fabric can be applied to thermoelectric generator and functional textiles.

Abstract

Inspired by worm morphology, this study report a low-cost and facile synthesis approach to construct a worm-like P-type flexible thermoelectric material—poly(3,4-ethylene dioxythiophene):p-toluenesulfonic acid (PEDOT:Tos) coated polypropylene (PP) nonwoven fabrics via low-temperature interfacial polymerization. This as-prepared thermoelectric fabric made of fibers with a core-shell structure has an electrical conductivity of 2.19 S/cm and the Seebeck coefficient of 16.15 μV K⁻¹ at a temperature difference of 30 °C. Furthermore, it presents good mechanical and washing stability by bending and ultrasonic test. A thermoelectric device designed of five pairs of thermoelectric material (p-type) and copper wire (n-type) generates 0.512 mV voltage at a temperature difference of 10 °C. This thermoelectric device has a prospect in the application of portable and interactive devices. This study proposes an easy way to manufacture bioinspired thermoelectric fabric with high thermoelectric performance and high potential applications, such as in wearable and flexible sensors.

Introduction

The shortage of fossil fuel becomes an inevitable challenge [1,2]{Xi, 2007 #86;Kalkan, 2012 #89;Kalkan, 2012 #136;Xi, 2007 #138;Kalkan, 2012 #136;Xi, 2007 #138}, thus the generation of sustainable clean sources desperately needs development and breakthrough. The thermoelectric device, using the seebeck effect to recycle the waste heat and low-grade heat, garners scholars’ attention. And the device has a simple structure, small volume, reliable safety, no pollution, and constant output electric supply [[3], [4], [5]]. Traditional thermoelectric materials are made of inorganic semiconductor materials, such as Bi₂Te₃, PbTe, and CoSb₃ [[6], [7], [8], [9]]. These materials feature a relatively higher thermoelectric effect, but they require high-cost components and possibly cause pollution of heavy metal [10]. Moreover, the costly processing facility, complex manufacturing process they demand preclude them from being used at a mass scale [10,11], meanwhile, the rigidity and brittleness of inorganic materials also restrict their applications. To sum up, the feasibility of upscaling thermoelectric materials is realized by a low production cost and better performance.

Conductive polymers, such as PANI [10], PTH [12], PEDOT [13], PA [14], and PPY [15], and their derivatives have a great potential to form organic thermoelectric materials that have feasible applications due to their good electrical conductivity, low thermal conductivity, lightweight, low production cost, flexibility, and ease of processing [11,16]. It is reported that pure PEDOT film has good thermoelectric effect and a dimensionless figure of merit (ZT) being 0.25 at room temperature [17], which is considerably high. Besides, PEDOT has good electrical conductivity, non-toxicity, environmental stability [18,19], which lead PEDOT to be a great candidate for thermoelectric application.

With good thermoelectric and flexible properties [18], PEDOT contributes good application prospects to the intelligent textile thermoelectric material field for wearable thermoelectric energy harvesting and body thermal energy management [20,21]. Therefore, fiber or fabric-based thermoelectric materials and device with PEDOT have emerged [22,23]. There are several manners to form PEDOT coated fabrics. Used as functional particles, PEDOT enwraps the fabrics via repeated saturation and drying [24,25]. In addition, it is also used to coat the fibers before another protecting layer [26] or mixed with water-based resin to combine with fabrics, thereby forming functional products [27]. Such products have certain thermoelectric functions. However, PEDOT:PSS products cost a lot but contain a little amount solid content on the surface of the fabric, which renders the resulted products with a high cost and low electrical conductivity [24]. In order to improve the quality of products made of PEDOT:PSS, some studies then conducted directly polymerization of PEDOT over the fabrics, thereby coating the fibers and as such obtained evenly distributed functional layer and good thermoelectric effect. For example, vapor deposition [20,[28], [29], [30]] is one way to vaporize and induce EDOT and FeCl₃ into fabric substrate for interaction, thereby producing PEDOT membranes with a thickness of 1.5 μm and low sheet resistances 44 Ω/□. The other way is electrochemical deposition [[31], [32], [33]], which is conducted by immersing electrically conductive substrates in an EDOT electrolyzing solution so as to deposit PEDOT over the functional products. However, these two methods have different limits. Vapor deposition needs a harsh working environment and expensive laboratory equipment whereas electrochemical deposition demands substrates with certain electrical conductivity, for which common textiles are not feasible. Therefore, it is desperate to make the PEDOT coated fabrics with an efficient and economical method. Chemical polymerization is a possible method while a common method is mechanical mixing that produces PEDOT fabrics using in situ polymerization. This method allows less deposit amount of PEDOT particles over the fabrics, and the adhesion level of PEDOT is higher over the middle region than the margins of fabrics. As a result, the electric fabrics have a low unevenness, which compromises the converting efficiency of useful PEDOT. Hence, interfacial polymerization is a better polymerization in order to reduce the influence of auxiliary operation on polymerization on the fabrics.

A worm has fold structure, leading to a large surface area. By utilizing the special fold appearance, more thermal radiation waves can be captured and consumed, so that the worm-like material can get more thermal energy. Therefore, this study uses low-cost PP nonwoven fabrics as the substrate of interfacial polymerization and generates worm-like PEDOT:Tos conductive case over the fibers at a low-temperature environment (-13 ℃). Thermoelectric nonwoven fabrics have an electrical conductivity of 2.19 S/cm and the seebeck coefficient of 16.15 μV K⁻¹ when the temperature difference is 30 °C. This low-temperature in situ polymerization enables the polymerized PEDOT to better adhere to the fiber of fabric. Furthermore, the bending and ultrasonic test are conducted to examine the mechanical stability and adhesion of the coating fabrics. The results demonstrated that the resulted electronic textiles have a certain stability and good flexibility, and thus can be bent and folded freely. Containing P-type thermoelectric nonwoven fabrics and copper wire sections, multiple-paired thermoelectric modules are designed to highlight the energy harvesting feature of the products.