Thermoelectric Nanocomposites Research Articles

A simple in-situ PZT oxide's decomposition: Realizing synergistic tailoring of electrical and thermal transport properties of BiCuSeO thermoelectric ceramics through band and phonon engineering

BiCuSeO, an oxide thermoelectric material with a superlattice structure, presents the advantages of affordability, low toxicity, and environmental friendliness. However, its intrinsic low electrical conductivity has impeded its possible applications. To address this challenge, we put tiny PbZr0.52Ti0.48O3 (PZT) with varying weight percentages (x = 0, 5, 7, 9, 11) into BiCuSeO (BCSO) to fabricate thermoelectric nanocomposites. Through the spark plasma sintering process, PZT particles underwent in-situ decomposition, generating nano-sized second phases such as PbO2, TiO2, and PbZrO3, which are homogenously distributed within BCSO matrix (validated by XRD and TEM). The introduced PbO2, TiO2, and PbZrO3 second phases served a dual purpose: inhibiting the grain growth of BCSO and introducing additional nano-grain boundaries. This resulted in more effective phonon scattering sites, thereby reducing lattice thermal conductivity. Simultaneously, the Pb element derived from PZT decomposition was doped into the Bi site of the BCSO matrix, causing a reduction in the band gap of BCSO from 0.49 eV to 0.388 eV and a significant increase in carrier concentration. Consequently, this doping enhanced the electrical conductivity of BCSO-based composites, with the composite with 11 wt% PZT additive amount exhibiting a remarkable 318-fold increase, reaching 550 S/cm compared to pristine BCSO. Notably, the composite with 7 wt% PZT additive amount achieved an exceptionally low lattice thermal conductivity of 0.333 W m−1 K−1 at 823 K. Through the synergistic optimization of electrical and thermal transport properties, the BCSO-based composite with 7 wt% PZT additive amount obtained a ZT value of ∼0.9 at 873 K, representing a 2.45-fold increase compared to pristine BiCuSeO. This straightforward method presents a cost-effective and scalable approach to enhance the thermoelectric performance of various materials, opening new avenues for potential commercial applications.

Evaluation of thermoelectric properties of hybrid polyaniline nanocomposites incorporated with graphene oxide and zinc oxide with different morphologies

Thermoelectric materials have been the object of interest in energy demand, given their potential for heat capture and the possibility of conversion into electricity. Among the possible thermoelectric materials, polymeric ones have been investigated because they are durable, non-toxic, and reproducible. This work used polyaniline (PANI), a good conductivity polymer, as a matrix to prepare hybrid nanocomposites. Nanoparticles were incorporated into the PANI matrix via solution with m-cresol. Two types of novel nanoparticles were used: zinc oxide (ZnO) synthesized with morphologies of nanoneedles (n-ZnO) and nanoflowers (f-ZnO). Hybrids of graphene oxide (GO) and ZnO with these morphologies (GO/n–ZnO and GO/f–ZnO) were incorporated into the hybrid PANI nanocomposites. Thermal stability was evaluated by thermogravimetric analysis (TGA). An improvement in thermal stability was observed with increasing GO/ZnO nanoparticles, as well as a higher degradation of the polymer matrix for higher levels of ZnO nanoparticles. The absorption bands of nanoparticles and PANI were observed by Fourier infrared spectroscopy (FT-IR). The corresponding characteristic bands of the functional groups were well evidenced, reflecting the success in synthesizing thermoelectric nanocomposites. Those with hybrid nanoparticles (GO/ZnO) had higher values of electrical conductivity (10.8 and 10.5 S cm−1), while those with only ZnO nanoparticles had higher Seebeck coefficient values (166.4 and 67.4 μV K−1). The only one with the highest thermoelectric force factor was PANI/GO/n-ZnO, with a value of 14.79 μW m−1 K−2, which is 49.3 times greater than the pure polymer and 1.5 times greater than the PANI/n-ZnO nanocomposite.

Modulation doping of p-type Cu12Sb4S13 toward improving thermoelectric performance

The commercial viability of thermoelectric (TE) devices relies heavily on two factors: cost reduction and efficiency enhancement. In this study, we first produce p-type Cu12Sb4S16–x (x = 0, 3, 4) using a low-temperature bottom-up approach and demonstrate Cu12Sb4S13 to show the best TE performance among the three tested compositions. Subsequently, the TE energy conversion efficiency of Cu12Sb4S13 is further enhanced by optimizing its electronic band structure through the incorporation of small amounts of tellurium. At an optimal Te content of 5 mol%, more than a twofold increase in the TE figure of merit (zT) is obtained. To gain insight into the mechanism of improvement on the transport properties of the material, we compare the interphase transport mechanism by incorporating nanodomains of different metals (Ag and Cu) into the Cu12Sb4S13 matrix. The improved electrical conductivity obtained with Cu12Sb4S13-Te nanocomposites is attributed to a charge flooding of the Cu12Sb4S13 surface. In contrast, excessive downward band-bending at the interphases of Ag/Cu metal-semiconductor drastically reduces the electrical conductivity. Besides, a weighted mobility (μw) analysis shows a dominant thermal activation of carriers in Cu12Sb4S13-Te nanocomposites. In this material, a strong decrease in lattice thermal conductivity is also found, which is associated with a phonon-carrier scattering mechanism. Our work shows the importance of proper band-engineering in TE nanocomposites to decouple electrical and thermal transport to enhance TE performance, and the efficacy of μw for electrical and thermal transport analysis.

Bismuthene nanosheets prepared by an environmentally friendly method and their thermoelectric epoxy nanocomposites

Theoretical research has predicted high thermoelectric performance for bismuthene nanosheets, but it is a great challenge to prepare these nanosheets due to low efficiency and intensive oxidation. We herein report an efficient, environmentally friendly preparation method for bismuthene nanosheets, each being 1–1.5 nm thick in average, through mechanochemical treatment with an ethanol system. The system was found to prevent adverse oxidation in comparison with a pure water system. Although neither the oxidation reactions nor the exfoliation could significantly change the Seebeck coefficient of bismuthene nanosheets, their power factor was measured as 155.6 ± 15.4 μW·m-1K-2. An epoxy nanocomposite was prepared containing 99 vol% of bismuthene nanosheets, to create a thermoelectric generator. It converted a temperature gradient of 11°C generated by human body into an electrical output of 18.62 nW. Our mechanochemical exfoliation method for the preparation of low-oxidation bismuth nanosheets offers insights for large-scale fabrication of nanosheets and their composites for industrial applications. It advances the field of thermoelectric nanocomposites.

Organic Thermoelectric Nanocomposites Assembled via Spraying Layer-by-Layer Method

Thermoelectric (TE) materials have been considered as a promising energy harvesting technology for sustainably providing power to electronic devices. In particular, organic-based TE materials that consist of conducting polymers and carbon nanofillers make a large variety of applications. In this work, we develop organic TE nanocomposites via successive spraying of intrinsically conductive polymers such as polyaniline (PANi) and poly(3,4-ethylenedioxy- thiophene):poly(styrenesulfonate) (PEDOT:PSS) and carbon nanofillers, and single-walled carbon nanotubes (SWNT). It is found that the growth rate of the layer-by-layer (LbL) thin films, which comprise a PANi/SWNT-PEDOT:PSS repeating sequence, made by the spraying method is greater than that of the same ones assembled by traditional dip coating. The surface structure of multilayer thin films constructed by the spraying approach show excellent coverage of highly networked individual and bundled SWNT, which is similarly to what is observed when carbon nanotubes-based LbL assemblies are formed by classic dipping. The multilayer thin films via the spray-assisted LbL process exhibit significantly improved TE performances. A 20-bilayer PANi/SWNT-PEDOT:PSS thin film (~90 nm thick) yields an electrical conductivity of 14.3 S/cm and Seebeck coefficient of 76 μV/K. These two values translate to a power factor of 8.2 μW/m·K2, which is 9 times as large as the same films fabricated by a classic immersion process. We believe that this LbL spraying method will open up many opportunities in developing multifunctional thin films for large-scaled industrial use due to rapid processing and the ease with which it is applied.

All-Solution-Processed Polythiophene/Carbon Nanotube Nanocomposites Integrated on Biocompatible Silk Fibroin Substrates for Wearable Thermoelectric Generators

This paper presents proof-of-concept all-solution-processed wearable thermoelectric generators made of single-walled carbon nanotube/poly(3-hexylthiophene) (SWCNT/P3HT) nanocomposites integrated with biocompatible silk fibroin substrates and Ag nanowires (NWs)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT/PSS) layers. Since well-dispersed SWCNT/P3HT nanocomposites are obtained through π–π interactions between conjugated backbones, continuous and repeated spraying/vacuum processes enabled the silk fibroin-substrated SWCNT/P3HT films to exhibit an optimized power factor of 204 ± 4.6 μW m–1 K–2 at 50 °C, an electrical conductivity of 1170 ± 52.8 S cm–1, and a Seebeck coefficient of 41.8 ± 0.9 μV K–1, which are ∼1.5 times those of the glass-substrated device. This may be attributed to the significantly enhanced conductivity caused by the increased junction density of the SWCNT bundles within the compact and dense SWCNT/P3HT nanocomposites. When a spray-patterned Ag NWs/PEDOT/PSS electrode was assembled, the constructed in-plane SWCNT/P3HT thermoelectric generators with 14 legs produced an open-circuit voltage (Voc) of 22.6 mV and a peak power of 25.1 nW at a temperature difference (ΔT) of 28.8 °C while maintaining good flexibility during bending tests. This demonstrates that these silk fibroin-substrated thermoelectric generator prototypes, which are worn on the forearm, can be used to harvest human body heat, thereby generating a Voc of ∼6.1 mV with a ΔT as low as 8.3 °C between the skin and surrounding air. This study offers a promising strategy for exploiting simple solution-processed thermoelectric nanocomposites assembled using biomass-based substrates and patterned electrodes for low-grade waste heat-harvesting wearable devices.

Enhanced thermoelectric composite performance from graphene nanosheets additives in AgSbTe2 matrix

The glass-like thermoelectric material AgSbTe2 has shown great potential in recent years due to its inherent low thermal conductivity and large Seebeck coefficient. Using nanostructured engineering to improve the electrical properties of AgSbTe2 while reducing its lattice thermal conductivity, is the main focus of thermoelectric performance optimization. Herein, we report a significant improvement in the thermoelectric performance of a composite prepared by incorporation of graphene nanosheets into surface-modified AgSbTe2 matrix via the hetero-aggregation method. Compared with the matrix, all composite bulk samples exhibited lower lattice thermal conductivity due to the enhanced phonon scattering at the new formed interfaces. Besides, the formation of the conductive network structure by graphene nanosheets in the matrix greatly increased the conductivity of AgSbTe2 from 1.6 to 2.5*104 S/m without significant deterioration of the Seebeck coefficient. Consequently, the maximum ZT of about 1.25 was obtained at 500K for 0.9 vol% graphene/AgSbTe2, which was 69% higher than that of pristine AgSbTe2 bulk. This also validates that the hetero-aggregation composite method is a promising processing scheme for designing novel two-dimensional thermoelectric nanocomposites.

Features of the Transport Properties of Thermoelectric Nanocomposites Based on a Matrix from BiSbTe1.5Se1.5 Medium-Entropy Alloy and Carbon-Nanotube Filler

For the first time, thermoelectric nanocomposites consisting of a BiSbTe1.5Se1.5 medium-entropy alloy (nanocomposite matrix) and “Taunit-M”, CNT carbon nanotubes (nanocomposite filler)are obtained. All BiSbTe1.5Se1.5 + xCNT nanocomposites with different filler contents (x = 0, 0.05, 0.1, 0.5, 1.0, 1.5, and 2.0 wt %), obtained by spark plasma sintering of the initial powders of the matrix material and filler, consist of micron-sized filler inclusions formed from clusters of nanotubes. The inclusions themselves are randomly distributed within the polycrystalline matrix. In the temperature range of 290–500 K, the transport properties (electrical resistivity and total thermal conductivity, including the electronic and phonon contributions, as well as the contribution of bipolar thermal conductivity) of the nanocomposites with various filler contents are studied. It is established that the introduction of CNTs into the matrix leads to a qualitative change in the type of electrical conductivity from “metallic” (electrical resistance increases with temperature), characteristic of the nanocomposite matrix, to “semiconductor” (resistance decreases with temperature), characteristic of nanocomposites. The observed “semiconductor” behavior of the electrical conductivity is characteristic of electrically inhomogeneous systems, in which current transfer is determined by the movement of electrons through the interfaces between the inhomogeneities. For all nanocomposites with different filler contents, the temperature dependences of the total thermal conductivity are qualitatively similar. At low temperatures, they are determined by the phonon contribution; at high temperatures, by the bipolar-thermal-conductivity contribution; the electronic contribution manifests itself at all temperatures, but it gradually decreases with increasing x. The minimum thermal conductivity is observed for the nanocomposite with x = 0.5 at % CNT.

Interfacial engineering of solution-processed Bi2Te3-based thermoelectric nanocomposites via graphene addition and liquid-phase-sintering process

Solution-processed Bi2Te3-based nanocomposites usually have rich nanostructures and interfaces that show great promise for promoting the thermoelectric performance according to the theoretical effects of “quantum confinement” and “topological insulator”. Here, an interfacial engineering strategy is developed to enhance the thermoelectric performance of n-type Bi2Te3-based nanocomposites upon synergistically introducing liquid-phase-sintering (LPS) process and adding graphene oxide (GO). Enhanced phonon scatterings by interfacial GO and various nanograins lead to an ultralow lattice thermal conductivity of ∼ 0.21 Wm-1K−1 at 398 K for the 1 wt% GO-added Bi2Te2.5Se0.5. Excess Te activated LPS process can improve the interfacial connection for good electrical conductivity without increasing the lattice thermal conductivity. The excess Te and addition of GO can also suppress the donor-like effect in Bi2Te3 for optimizing the carrier concentration. Due to these synergetic effects, a peak figure of merit (ZT) of ∼ 1.03 at 473 K and an average ZT of ∼ 0.85 within 300–473 K can be achieved in the 1 wt% GO-added sample. A single-couple TE device is also made using our n-type 1 wt% GO-added Bi2Te2.5Se0.5 and the traditional p-type Bi0.5Sb1.5Te3, showing a maximum power density of ∼ 0.06 Wcm−2 at temperature difference of 154.8 K. Moreover, the difference between GO and nitrogen-doped graphene as additives is also systematically discussed, providing a guide for the rational use of graphene in interfacial design.

A simple method for fabricating flexible thermoelectric nanocomposites based on bacterial cellulose nanofiber and Ag2Se

Flexible thermoelectric (FTE) devices have become attractive in recent years since they can be utilized as a power generator for wearable and portable electronics. This work fabricated FTE nanocomposites from bacterial cellulose (BC) and Ag2Se via an easy and inexpensive method. The blended BC was thoroughly mixed with Ag2Se powders before casting onto a filter paper via vacuum filtration, followed by oven-drying and hot-pressing. Phase formation of Ag2Se in the BC nanofiber network was confirmed by x-ray diffraction and energy dispersive spectroscopy. SEM images revealed the distribution of Ag2Se particles in the BC matrix. The Ag2Se particles were densely packed for large Ag2Se concentrations in the BC/Ag2Se nanocomposite. Thermoelectric measurements found that the electrical conductivity (σ) and Seebeck coefficient (S) varied with the Ag2Se proportion due to the changes in the carrier concentration and carrier mobility. The maximum σ of 5.7 × 104 S/m and S of −80 μV/K were observed at room temperature (RT), yielding the power factor (PF) of ∼300 μW/mK2. This PF value is comparable to other FTE materials, but the process used in this research is much simpler. The thermal conductivity was 0.56 W/mK at RT. Moreover, the BC/Ag2Se nanocomposites were highly flexible and could be attached to curved surfaces. In addition, the FTE module was constructed from BC/Ag2Se uni-leg elements, which could generate an output power of 0.28 μW. In addition, the simple fabrication process makes the BC/Ag2Se nanocomposite readily expandable to an industrial scale for modern FTE devices.

Preparation of antimonene nanosheets and their thermoelectric nanocomposites

Having high stability, carrier mobility and band gap tunability, antimonene nanosheets hold promise for thermoelectric applications. However, due to low production yield and oxidization, relevant studies have focused on theoretical prediction and numerical simulation. We herein report a liquid-phase exfoliation method with a novel solvent system of amine-terminated polyether (Jeffamine ED 2003): ethanol = 1:4 (weight ratio) for preparation of antimonene nanosheets. This method not only effectively inhibited the oxidation of antimonene nanosheets but produced a low thickness of 2.0 ± 0.5 nm; a film consisting of the nanosheets exhibited an electrical conductivity of 1800.1 ± 97.4 S/cm and a thermoelectric power factor of 118.9 ± 5.6 μW m−1 K−2. An epoxy nanocomposite film containing 99 vol% antimonene nanosheets demonstrated sufficient mechanical resilience for assembling of a thermoelectric generator. With a human body temperature gradient of 11 °C, the generator created a voltage of 0.471 mV and a current of 21.578 μA, leading to a power output of 10.16 nW. This study also investigated the lithium-ion intercalation method as a benchmark for preparation of antimonene nanosheets.

Printed Flexible Thermoelectric Nanocomposites Based on Carbon Nanotubes and Polyaniline.

A new era of composite organic materials, nanomaterials, and printed electronics is emerging to the applications of thermoelectric generators (TEGs). Special attention is focused on carbon nanomaterials and conducting polymers, and the possibility to form pastes and inks for various low-cost deposition techniques. In this work, we present a novel approach to the processing of composite materials for screen-printing based on carbon nanotubes (CNTs) and polyaniline (PANI), supported with a dielectric polymer vehicle. Three different types of such tailor-made materials were prepared, with a functional phase consisted of carbon nanotubes and polyaniline composites fabricated with two methods: dry mixing of PANI CNT powders and in situ polymerisation of PANI with CNT. These materials were printed on flexible polymer substrates, exhibiting outstanding mechanical properties. The best parameters obtained for elaborated materials were , , and , respectively.

Energy-Filtered Acceleration of Charge-Carrier Transport in Organic Thermoelectric Nanocomposites

Energy-Filtered Acceleration of Charge-Carrier Transport in Organic Thermoelectric Nanocomposites

Polymer-Inorganic Thermoelectric Nanomaterials: Electrical Properties, Interfacial Chemistry Engineering, and Devices.

Though solar cells are one of the promising technologies to address the energy crisis, this technology is still far from commercialization. Thermoelectric materials offer a novel opportunity to convert energy between thermal and electrical aspects, which show the feasibility to improve the performance of solar cells via heat management and light harvesting. Polymer–inorganic thermoelectric nanocomposites consisting of inorganic nanomaterials and functional organic polymers represent one kind of advanced hybrid nanomaterials with tunable optical and electrical characteristics and fascinating interfacial and surface chemistry. During the past decades, they have attracted extensive research interest due to their diverse composition, easy synthesis, and large surface area. Such advanced nanomaterials not only inherit low thermal conductivity from polymers and high Seebeck coefficient, and high electrical conductivity from inorganic materials, but also benefit from the additional interface between each component. In this review, we provide an overview of interfacial chemistry engineering and electrical feature of various polymer–inorganic thermoelectric hybrid nanomaterials, including synthetic methods, properties, and applications in thermoelectric devices. In addition, the prospect and challenges of polymer–inorganic nanocomposites are discussed in the field of thermoelectric energy.

Magnetoresistance-enhanced electro-thermal conversion performance

Seeking novel and effective approaches to synergistically improve the electrical and thermal transport properties and electro-thermal conversion efficiency of Bi2Te3-based alloys is essential for commercial applications. Here, GdCo2/Bi0.37Sb1.63Te3 thermoelectric nanocomposites were designed and synthesized to achieve synergistic improvement of electrical and thermal properties. As confirmed by magnetoresistance measurement, the built-in magnetic field and magnetic scattering generated by magnetic nanoparticles decrease the carrier concentration and mobility, and increase the Seebeck coefficient. Meanwhile, GdCo2 nanoparticles lead to broad-frequency phonon scattering, which effectively reduces the lattice thermal conductivity of nanocomposites. Eventually, the average ZT of the nanocomposite is increased by 18% in the range of 300–500 K, and the cooling temperature difference is increased by 68% near room temperature. This work proves that the thermoelectromagnetic coupling effects generated by magnetic particles can effectively improve the electro-thermal conversion performance.

Assessment of Thermoelectric, Mechanical, and Microstructural Reinforcement Properties of Graphene-Mixed Heterostructures

We examine the role of graphene nanoplates (GNPs) in the critical properties of thermoelectric GNP nanocomposites. After a detailed analysis of the thermoelectric, microstructural, and mechanical c...

High-performance cement/SWCNT thermoelectric nanocomposites and a structural thermoelectric generator device towards large-scale thermal energy harvesting

For the first time, the thermoelectric properties of cement/single-walled carbon nanotube (SWCNT) nanocomposites with over 3, 7, 14 and 28 days of hydration are reported, while a thermoelectric generator device (TEG) is fabricated utilising the material with the highest achieved power factor (PF).

Correction: Semiconducting polymer contributes favorably to the Seebeck coefficient in multi-component, high-performance n-type thermoelectric nanocomposites

Correction for ‘Semiconducting polymer contributes favorably to the Seebeck coefficient in multi-component, high-performance n-type thermoelectric nanocomposites’ by Junhui Tang et al., J. Mater. Chem. A, 2020, 8, 9797–9805, DOI: 10.1039/d0ta02388d.

MWCNT/Thienothiophene based All-Organic thermoelectric composites: Enhanced performance by realigning of the Fermi level through doping

Thermoelectric (TE) polymer nanocomposites are an emerging class of functional materials that have immense potential for commercial usage. In this work, a lightweight all-organic nanocomposite of benzodithiophene-thienothiophene (BDT-TTE) based conjugated polymer poly[4,8-bis(5-(2-ethylyhexyl)thiophene-2-yl)benzo[1,2-b;4,5-b’]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)3-fluorothieno[3,4-b’]thiophene-)-2-carboxylate-2–6-diyl)] (PBDTT-FTTE) and multi-walled carbon nanotube (MWCNT) was prepared for TE applications. The peak electrical conductivity in the composite was obtained with 45 wt% MWCNT content and the resulting composite exhibited a temperature tolerance up to 350 °C. The as-prepared nanocomposite was further p-doped with an oxidizing agent for tuning its Fermi level positioning leading to the further enhancement in TE output. The electrical conductivity was further boosted by 6.7x post-doping with concurrent 2.5x enhancement in the Seebeck coefficient. Thus, the power factor increased from 1.28 µW/m.K2 to 48.21 µW/m.K2, leading to the highest value for the thienothiophene based conjugated polymer/MWCNT nanocomposite. The device performance was demonstrated with a prototype exhibiting the power delivery of ~ 7 nW/cm2 when tested with applied temperature difference across the hot and cold junction of 65 K.

Organic thermoelectric thin films with large p-type and n-type power factor

P- and n-type thermoelectric (TE) materials were prepared by using a layer-by-layer method. Assembled nanocomposites displayed high TE properties. For the p-type nanocomposites, polyaniline (PANi)/graphene-poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)/PANi/carbon nanotubes (CNT)-PEDOT:PSS quadlayers (QL) were assembled by immersing a substrate alternately to aqueous solutions of these charged materials. Various concentrations of three types of CNT (single-walled, double-walled (DWNT), and multi-walled) and two different surface areas of graphene (300 and 750 m2 g−1) were investigated. The best QL films, assembled with graphene and DWNT, exhibit a power factor (PF = S2 σ) of 3050 µW m−1 K−2 at room temperature, which is among the highest values for a fully organic material. In an effort to improve TE properties in n-type organic thin films, hydrazine is introduced to the films in which DWNT, stabilized by polyethylenimine (PEI), is alternately deposited with graphene, stabilized by polyvinylpyrrolidone (PVP). After doping these films for 5 min with hydrazine, electrical conductivity and Seebeck coefficient significantly increase. An 80 DWNT-PEI/graphene-PVP bilayer film achieves a PF as high as 380 µW m−1 K−2 at room temperature, exhibiting a twofold improvement relative to that of un-doped films. In light of the growing interest in organic thermoelectric nanocomposites, this study provides an effective means to achieve high performance that will allow these unique materials to replace inorganic semiconductors in some applications.