Hybrid Thermoelectric Materials Research Articles

Oxidation Control to Augment Interfacial Charge Transport in Te-P3HT Hybrid Materials for High Thermoelectric Performance.

Organic-inorganic hybrid thermoelectric (TE) materials have attracted tremendous interest for harvesting waste heat energy. Due to their mechanical flexibility, inorganic-organic hybrid TE materials are considered to be promising candidates for flexible energy harvesting devices. In this work, enhanced TE properties of Tellurium (Te) nanowires (NWs)- poly (3-hexylthiophene-2, 5-diyl) (P3HT) hybrid materials are reported by improving the charge transport at interfacial layer mediated via controlled oxidation. A power factor of ≈9.8µW(mK2)-1 is obtained at room temperature for oxidized P3HT-TeNWs hybrid materials, which increases to ≈64.8µW(mK2)-1 upon control of TeNWs oxidation. This value is sevenfold higher compared to P3HT-TeNWs-based hybrid materials reported in the literature. MD simulation reveals that oxidation-free TeNWs demonstrate better templating for P3HT polymer compared to oxidized TeNWs. The Kang-Snyder model is used to study the charge transport in these hybrid materials. A large σE0 value is obtained which is related to better templating of P3HT on oxygen-free TeNWs. This work provides evidence that oxidation control of TeNWs is critical for better interface-driven charge transport, which enhances the thermoelectric properties of TeNWs-P3HT hybrid materials. This work provides a new avenue to improve the thermoelectric properties of a new class of hybrid thermoelectric materials.

Ambient-Stable n-Type Carbon Nanotube/Organic Small-Molecule Thermoelectrics Enabled by Energy Level Control.

The stability of n-type organic and hybrid thermoelectric materials is limited in terms of their practical application to p-n parallel thermoelectric devices. We demonstrate the ambient stability of an n-type single-walled carbon nanotube/organic small-molecule (SWNT/OSM) hybrid by deepening the lowest occupied molecular orbital energy level. This hybrid exhibited the best figure of merit (0.032) among n-type SWNT/OSM hybrid thermoelectrics and an enhanced power factor of 291.0 μW m-1 K-2. Furthermore, we observed that the n-type thermoelectric stability of a hybrid of SWNT and pip containing two N-ethylpiperidinyl groups on both sides of a naphthalenediimide core was retained at 87% over 7 months (220 days) under ambient conditions without encapsulation.

Influence of microstructure and thermoelectric properties on the power density of multi-walled carbon nanotube/ metal oxide hybrid flexible thermoelectric generators

The quest for a low-cost, flexible thermoelectric generator using eco-friendly metal oxide-based materials for low-temperature applications has motivated this work. The work compares the performance of amine-functionalized multi-walled carbon nanotubes (MWCNT-NH2) and metal oxide nanoparticles (CuO, NiO, and Fe2O3) ink-based hybrid flexible thermoelectric generators. Study reveals that the thermoelectric performance of a flexible thermoelectric generator improves by fine-tuning the materials crystallite size, bandgap, carrier concentration, carrier mobility, resistivity, the Seebeck coefficient, and micro-porosity of the ink film, which could be materialized by using hybrid thermoelectric materials. Among the three fabricated devices, MWCNT-NH2/NiO hybrid flexible thermoelectric generator exhibits a maximum power output of 1.44 nW at ΔT= 100 °C. The maximum power density displayed by MWCNT-NH2/NiO hybrid device is 59.3 nW/cm2 at ΔT= 100 °C, which is 23.28% and 332.8% higher than that of MWCNT-NH2/CuO and MWCNT-NH2/Fe2O3-based devices, respectively. The performance of MWCNT-NH2/NiO is comparatively superior to some previously reported works.

Flexible Bi2Te3/PEDOT nanowire sandwich-like films towards high-performance wearable cross-plane thermoelectric generator and temperature sensor array

Flexible Bi2Te3/PEDOT nanowire sandwich-like films with a zT of 0.27 were fabricated for cross-plane wearable thermoelectric generation and thermal mapping.

Energy Level Modulation of Small Molecules Enhances Thermoelectric Performances of Carbon Nanotube-Based Organic Hybrid Materials.

Although numerous thermoelectric materials based on single-walled carbon nanotubes (SWNTs) and organic semiconductors have been reported during the past decade, the correlation between energy levels of organic semiconductors and thermoelectric performances of their hybrids is still ambiguous. In this study, we demonstrate that simultaneous modulation of the bandgap and highest occupied molecular orbital levels in organic small molecules (OSMs) largely improves the Seebeck coefficient and thus maximizes the figure of merit (ZT) of SWNT/OSM hybrids. SWNT/CzS with an enlarged bandgap and reduced barrier energy exhibited a synergistic increment in the Seebeck coefficient (108.7 μV K-1) and power factor (337.2 μW m-1 K-2), with the best ZT of 0.058 at room temperature among dopant-free carbon nanotube-hybridized thermoelectrics. The efficient charge carrier transport and reduced thermal conductivity of SWNT/CzS provided enhanced thermoelectric performance. Our strategy based on energy level modulation could be broadly applied for performance enhancement of organic and hybrid thermoelectric materials.

Enhanced Thermoelectric Properties of Composites Prepared With Poly(3,4-Ethylenedioxythiophene) Poly(Styrenesulfonate) and Vertically Aligned Se Wire.

Controlling the electronic transport behavior in thermoelectric composites is one of the most promising approaches to enhance their power factor because this enables decoupling of the correlation between the electrical conductivity and Seebeck coefficient. Herein, we show that the unexpected high power factor of the Se nanowire array embedded in poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) can be achieved by controlling the interfacial band structure engineering. The electrical conductivity and Seebeck coefficient simultaneously increased, confirming that the synthesis of organic/inorganic hybrid thermoelectric materials with improved performance was possible. Our exploration can be helpful for the rational design of high-performance thermoelectric composites through interface engineering.

Self‐Healable Organic–Inorganic Hybrid Thermoelectric Materials with Excellent Ionic Thermoelectric Properties

AbstractSelf‐healable and stretchable thermoelectric (TE) materials provide new possibilities for self‐powered flexible wearable devices to self‐repair mechanical damage. However, developing high‐performance materials with such desirable TE and mechanical properties is a significant challenge. In this work, organic–inorganic ionic TE composites (OITCs) with an unprecedently high ionic TE figure of merit (ZTi = 3.74 at 80% relative humidity) and robust properties of simultaneous self‐healing and stretching are reported. The OITCs are developed by incorporating inorganic SiO2 nanoparticles (SiO2‐nps) in a polyaniline: poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid): phytic acid (PANI:PAAMPSA:PA) ternary polymer. The incorporated SiO2‐nps constructively interact with the hybrid polymer to provide autonomous self‐healability and stretchability while augmenting the mobile proton concentration in OITCs, which substantially improves their ionic TE properties (i.e., ionic Seebeck coefficient and ionic conductivity). Moreover, the OITCs remain repeatedly stretchable and self‐healable under severe external stresses (50 cycles of 100% strain and 25 cycles of cutting/healing) without degradation of their TE properties. Using the OITCs with multi‐walled carbon nanotube electrodes, an ionic TE supercapacitor (ITESC) with a maximum energy density of 19.4 mJ m−2 is demonstrated upon a temperature difference of 1.8 K.

Thermoelectric Materials for Textile Applications.

Since prehistoric times, textiles have served an important role–providing necessary protection and comfort. Recently, the rise of electronic textiles (e-textiles) as part of the larger efforts to develop smart textiles, has paved the way for enhancing textile functionalities including sensing, energy harvesting, and active heating and cooling. Recent attention has focused on the integration of thermoelectric (TE) functionalities into textiles—making fabrics capable of either converting body heating into electricity (Seebeck effect) or conversely using electricity to provide next-to-skin heating/cooling (Peltier effect). Various TE materials have been explored, classified broadly into (i) inorganic, (ii) organic, and (iii) hybrid organic-inorganic. TE figure-of-merit (ZT) is commonly used to correlate Seebeck coefficient, electrical and thermal conductivity. For textiles, it is important to think of appropriate materials not just in terms of ZT, but also whether they are flexible, conformable, and easily processable. Commercial TEs usually compromise rigid, sometimes toxic, inorganic materials such as bismuth and lead. For textiles, organic and hybrid TE materials are more appropriate. Carbon-based TE materials have been especially attractive since graphene and carbon nanotubes have excellent transport properties with easy modifications to create TE materials with high ZT and textile compatibility. This review focuses on flexible TE materials and their integration into textiles.

Improving the thermoelectric performance of solution-processed polymer nanocomposites by introducing platinum acetylides with tailored intermolecular interactions

Hybrid thermoelectric (TE) materials incorporated with the conjugated polymers and single-walled carbon nanotubes (SWCNTs) are promising to decouple the intractable interrelation of the key TE parameters, and therefore yield considerable composites for solution-processable flexible TE generators. However, the disordered intermolecular interactions and inefficient overlap of the frontier molecular orbitals between the polymer backbones and the SWCNTs largely degenerate the TE properties of the composites. Herein, we demonstrate an efficient strategy to regulate their intermolecular π-π interactions by introducing heavy metal atoms (platinum) along with tailored π-ligands to reconstruct the main chain of the incorporated polymers. Consequently, both the calculated binding energy and the observed Dexter energy transfer process between the SWCNTs and the polymers are remarkably increased with the insertion of platinum, indicating significantly enhanced π-π interactions between the two. Meanwhile, their self-aggregation can be effectively restrained by the large steric hindrance groups of tributyl phosphine ligands synchronously. Therefore, a high power factors of over 464 μW m−1 K−2 (r.t.) and a high output power approaching to 2200 nW (ΔT = 70 K, 10 legs) can be achieved by the P(HTh-Pt)/SWCNT-based TE generators, which is almost two times as high as the homologous P3HT one without platinum.

Paper Thermoelectrics by a Solvent-Free Drawing Method of All Carbon-Based Materials.

As practical interest in the flexible or wearable thermoelectric generators (TEGs) has increased, the demand for the high-performance TEGs based on ecofriendly, mechanically resilient, and economically viable TEGs as alternatives to the brittle inorganic materials is growing. Organic or hybrid thermoelectric (TE) materials have been employed in flexible TEGs; however, their fabrication is normally carried out using wet processing such as spin-coating or screen printing. These techniques require materials dissolved or dispersed in solvents; thus, they limit the substrate choice. Herein, we have rationally designed solvent-free, all carbon-based TEGs dry-drawn on a regular office paper using few-layered graphene (FLG). This technique showed very good TE parameters, yielding a power factor of 97 μW m–1 K–2 at low temperatures. The p-type only device exhibited an output power of up to ∼19.48 nW. As a proof of concept, all carbon-based p-n TEGs were created on paper with the addition of HB pencil traces. The HB pencil exhibited low Seebeck coefficients (−7 μV K–1), and the traces were highly resistive compared to FLG traces, which resulted in significantly lower output power compared to the p-type only TEG. The demonstration of all carbon-based TEGs drawn on paper highlights the potential for future low-cost, flexible, and almost instantaneously created TEGs for low-power applications.

Hybrid Thermoelectrics

Constructing hybrid composites with organic and inorganic materials at different length scales provides unconventional opportunities in the field of thermoelectric materials, which are classified as hybrid crystal, superlattice, and nanocomposite. A variety of new techniques have been proposed to fabricate hybrid thermoelectric materials with homogeneous microstructures and intimate interfaces, which are critical for good thermoelectric performance. The combination of organic and inorganic materials at the nano or atomic scale can cause strong perturbation in the structural, electron, and phonon characteristics, providing new mechanisms to decouple electrical and thermal transport properties that are not attainable in the pure organic or inorganic counterparts. Because of their increasing thermoelectric performance, compositional diversity, mechanical flexibility, and ease of fabrication, hybrid materials have become the most promising candidates for flexible energy harvesting and solid-state cooling.

Development of Organic and Inorganic Ternary Hybrid Thermoelectric Materials Using Ag Nanoplates

Development of Organic and Inorganic Ternary Hybrid Thermoelectric Materials Using Ag Nanoplates

A Brief Review on Measuring Methods of Thermal Conductivity of Organic and Hybrid Thermoelectric Materials

AbstractOrganic and hybrid thermoelectric (OHT) materials have attracted increasing research interest over the past decade. Thermal conductivity measurement plays a critical role in evaluating and improving the thermoelectric performance of various types of these novel materials, ranging from bulks to low‐dimensional structures. Commonly used and newly developed techniques for thermal conductivity measurement, most of which have been applied to OHT materials in recent years, are reviewed. They are categorized as steady‐state methods, time‐domain methods, or frequency‐domain methods. The operating principles, merits and limitations, technical issues, and application examples for each technique are also discussed.

Conductive polymer based high-performance hybrid thermoelectrics: Polyaniline/tin(II) sulfide nanosheet composites

Composites of tin sulfide (SnS) nanosheets with conductive polyaniline (PANI) are fabricated to achieve high-performance hybrid thermoelectric materials. SnS nanosheets with lateral sizes from 200 to 500 nm are prepared from a SnS ingot by applying a Li + -intercalation and chemical exfoliation process and are incorporated with conductive PANI. The thermoelectric power factor of the SnS nanosheet/PANI composites is optimized by manipulating the content of SnS nanosheets in the composite, and the changes in the thermoelectric properties are examined and discussed with respect to the carrier transport properties. The maximum ZT of 0.29 × 10−2 is obtained with the SnS nanosheet/PANI composite containing 20 wt% of SnS nanosheets, attributed to the dominance of the improvement in the Seebeck coefficient over the reduction in the electrical conductivity. The incorporation of conductive PANI and SnS nanosheets is a promising strategy for the actualization of high-performance thermoelectric applications.

Wearable and flexible thermoelectrics for energy harvesting

Abstract

Individual Adjustment of Electrical Conductivity and Thermopower Enabled by Multiple Interfaces in Polyaniline‐Based Ternary Hybrid Nanomaterials for High Thermoelectric Performances

AbstractRecent developed conducting polymer based hybrid thermoelectric (TE) materials provide a promising alternative route for energy conversion on a large scale. However, high thermopower largely relies on high content of low‐abundance elements, such as tellurium, which impedes the mass production of these materials. To optimize the compositions of the hybrids and further improve the TE properties, interfacial engineering is therefore employed to modulate the carrier transport properties in rationally designed multiwalled carbon nanotubes (MWCNTs)‐Te nanorod/polyaniline (PANI) ternary hybrid nanomaterials considering the similar π–π conjugated interactions among these constituents. The effects of MWCNTs and Te nanorods, especially the multiple interfaces formed between the constituents, on the TE performances and carrier transport behavior are studied in depth. Due to simultaneous increase in both electrical conductivity and thermopower, an optimal power factor of 54.4 µW m−1 K−2 is obtained in 52%Te‐16% MWCNT/PANI film, which is almost twice the value of binary Te/PANI film at the same Te content and comparable to that of 60% Te/PANI film. Moreover, the ternary hybrid film shows good mechanical stability. This study demonstrates an effective strategy to improve TE performances of conducting polymer based hybrids and has great potential for cost‐effective flexible energy conversion devices.

Structural, Electronic, and Transport Properties of Hybrid SrTiO3-Graphene and Carbon Nanoribbon Interfaces

Hybrid materials composed of different functional structural units offer the possibility of tuning both the thermal and electronic properties of a material independently. Using quantum mechanical calculations, we investigate the change in the electronic and thermoelectric transport properties of graphene and hydrogen-terminated carbon nanoribbons (CNRs) when these are placed on the SrTiO3 (001) surface (STO). We predict that both p-type and n-type composite materials can be achieved by coupling graphene/CNR to different surface terminations of STO. We show that the electronic properties of graphene and CNR are significantly altered on SrO-terminated STO but are preserved upon interaction with TiO2-terminated STO and that CNRs possess distinct electronic states around the Fermi level because of their quasi-one-dimensional nature, leading to a calculated Seebeck coefficient much higher than that of a pristine graphene sheet. Moreover, our calculations reveal that in the TiO2-SrTiO3/CNR system there is a favorable electronic level alignment between the CNR and STO, where the highest occupied molecular orbital of the CNR is positioned in the middle of the STO band gap, resembling n-type doping of the substrate. Our results offer design principles for guiding the engineering of future hybrid thermoelectric materials and, more generally, nanoelectronic materials comprising oxide and graphitic components.

Organic-Inorganic Hybrid Thermoelectric Material Synthesis and Properties

Organic-inorganic hybrid thermoelectric materials have obtained increasing attention because it opens the possibility of enhancing thermoelectric performance by utilizing the low thermal conductivity of organic thermoelectric materials and the high Seebeck coefficient of inorganic thermoelectric materials. Moreover, the organic-inorganic hybrid thermoelectric materials possess numerous advantages, including functional aspects such as flexibility or transparency, low cost raw materials, and simplified fabrication processes, thus, allowing for a wide range of potential applications. In this study, the types and synthesis methods of organic-inorganic thermoelectric hybrid materials were discussed along with the methods used to enhance their thermoelectric properties. As a key factor to maximize the thermoelectric performances of hybrid thermoelectric materials, the nanoengineering to control the nanostructure of the inorganic materials as well as the modification of the organic material structure and doping level are considered, respectively. Meanwhile, the interface between the inorganic and organic phase is also important to develop the hybrid thermoelectric module with excellent reliability and high thermoelectric efficiency in addition to its performance in various electronic devices. Key words: Thermoelectric, Organic-inorganic hybrid thermoelectric materials, Nanoengineering, Thermoelectric properties

Thermostability of Hybrid Thermoelectric Materials Consisting of Poly(Ni-ethenetetrathiolate), Polyimide and Carbon Nanotubes.

Three-component organic/inorganic hybrid films were fabricated by drop-casting the mixed dispersion of nanodispersed-poly(nickel 1,1,2,2-ethenetetrathiolate) (nano-PETT), polyimide (PI) and super growth carbon nanotubes (SG-CNTs) in N-methylpyrrolidone (NMP) at the designed ratio on a substrate. The dried nano-PETT/PI/SG-CNT hybrid films were prepared by the stepwise cleaning of NMP and methanol, and were dried once more. The thermoelectric properties of Seebeck coefficient S and electrical conductivity σ were measured by a thin-film thermoelectric measurement system ADVANCE RIKO ZEM-3M8 at 330–380 K. The electrical conductivity of nano-PETT/PI/SG-CNT hybrid films increased by 1.9 times for solvent treatment by clearing insulated of polymer. In addition, the density of nano-PETT/PI/SG-CNT hybrid films decreased 1.31 to 0.85 g·cm−3 with a decrease in thermal conductivity from 0.18 to 0.12 W·m−1·K−1. To evaluate the thermostability of nano-PETT/PI/SG-CNT hybrid films, the samples were kept at high temperature and the temporal change of thermoelectric properties was measured. The nano-PETT/PI/SG-CNT hybrid films were rather stable at 353 K and kept their power factor even after 4 weeks.

Thermoelectric transport in hybrid materials incorporating metallic nanowires in polymer matrix

We propose a type of thermoelectric materials incorporating metallic nanowires in insulating polymers. It is shown that the hybridization of poor thermoelectric materials such as metal and polymer can achieve high performance of thermoelectricity. The electrical conductivity of such hybrid materials is controllable by the volume fraction of metallic nanowires which is above a percolation critical value. Meanwhile, the Seebeck coefficient shows a weak dependence on the volume fraction. Low thermal conductivities required for achieving the high figure of merit can be fulfilled from both the low thermal conductivity of polymer and the interfacial thermal resistance between nanowires and polymer. In this regard, we propose the concept “electron-percolation thermal-insulator,” providing a guide to design efficient hybrid thermoelectric materials.