Composite Thermoelectric Materials Research Articles

Ultra-Low Thermal Conductivity and Improved Thermoelectric Performance in Tungsten-Doped GeTe.

Compared to SnTe and PbTe base materials, the GeTe matrix exhibits a relatively high Seebeck coefficient and power factor but has garnered significant attention due to its poor thermal transport performance and environmental characteristics. As a typical p-type IV-VI group thermoelectric material, W-doped GeTe material can bring additional enhancement to thermoelectric performance. In this study, the introduction of W, Ge1-xWxTe (x = 0, 0.002, 0.005, 0.007, 0.01, 0.03) resulted in the presence of high-valence state atoms, providing additional charge carriers, thereby elevating the material's power factor to a maximum PFpeak of approximately 43 μW cm-1 K-2, while slightly optimizing the Seebeck coefficient of the solid solution. Moreover, W doping can induce defects and promote slight rhombohedral distortion in the crystal structure of GeTe, further reducing the lattice thermal conductivity κlat to as low as approximately 0.14 W m-1 K-1 (x = 0.002 at 673 K), optimizing it to approximately 85% compared to the GeTe matrix. This led to the formation of a p-type multicomponent composite thermoelectric material with ultra-low thermal conductivity. Ultimately, W doping achieves the comprehensive enhancement of the thermoelectric performance of GeTe base materials, with the peak ZT value of sample Ge0.995W0.005Te reaching approximately 0.99 at 673 K, and the average ZT optimized to 0.76 in the high-temperature range of 573-723 K, representing an increase of approximately 17% compared to pristine GeTe within the same temperature range.

Advances in Nanoparticle-Enhanced Thermoelectric Materials from Synthesis to Energy Harvesting: A Review.

This comprehensive review analysis examines the domain of composite thermoelectric materials that integrate nanoparticles, providing a critical assessment of their methods for improving thermoelectric properties and the procedures used for their fabrication. This study examines several approaches to enhance power factor and lattice thermal conductivity, emphasizing the influence of secondary phases and structural alterations. This study investigates the impact of synthesis methods on the electrical characteristics of materials, with a particular focus on novel techniques such as electrodeposition onto carbon nanotubes. The acquired insights provide useful guidance for the creation of new thermoelectric materials. The review also compares and contrasts organic and inorganic thermoelectric materials, with a particular focus on the potential of inorganic materials in the context of waste heat recovery and power production within industries. This analysis highlights the role of inorganic materials in improving energy efficiency and promoting environmental sustainability.

Enhancement of thermoelectric properties in Sr0.7Ba0.3Nb2O6−δ-based ceramics via nano-sized Ti as additive

A series of Sr0.7Ba0.3Nb2O6−δ/x wt. % Ti (x = 1, 3, 5, and 10) composite ceramic thermoelectric materials were prepared, and the mechanism for improving their thermoelectric properties was explored. The experimental results demonstrate that nano-additive titanium powder undergoes oxidation to form TiO2 during sintering. However, under annealing in a reducing atmosphere, oxidation reactions further deplete the lattice oxygen, leading to an increased generation of oxygen vacancies and enhanced carrier concentration, ultimately leading to successful resistivity reduction. The samples consistently exhibit low thermal conductivity values below 2.0 W m−1 K−1 due to crystal defects, complex structure, and phonon scattering at the grain boundaries. The sample doped with 5 wt. %. Ti exhibits the lowest resistivity and highest PF value (409.3 μW/m K2 at 1073 K). Consequently, the figure of merit of Sr0.7Ba0.3Nb2O6−δ with 5 wt. % Ti attains its maximum value of 0.30 at 1073 K, representing a 50% increase compared to that of the undoped sample Sr0.7Ba0.3Nb2O6−δ (0.20 at 1073 K).

PREPARATION AND THERMOELECTRIC PROPERTIES OF Cux/Bi2Te3 COMPOSITES

Thermoelectric materials are the use of solid internal carriers to realize mutual conversion between thermal energy to electrical energy. Bismuth telluride (Bi<sub>2</sub>Te<sub>3</sub>) based thermoelectric materials are relatively mature near low temperatures. Due to the excellent conductivity of copper, the method of combining copper with a thermoelectric matrix to produce thermoelectric composite materials with better thermoelectric properties has always been a research focus in thermoelectric composite materials. Bismuth telluride thermoelectric composite materials (Cu<sub>x</sub>/Bi<sub>2</sub>Te<sub>3</sub>) samples with different mass percentages of purity (Cu) powder were prepared by spark plasma sintering (SPS) method. The influences of the Cu with different incorporation ratios on the performance of Cu<sub>x</sub>/Bi<sub>2</sub>Te<sub>3</sub> thermoelectric composites were investigated, such as differential thermal conductivity, thermal conductivity, Seeback coefficient, and ZT values. The Cu<sub>x</sub>/Bi<sub>2</sub>Te<sub>3</sub> thermoelectric composites with Cu chemical composition of 0.005 exhibited excellent Seebeck coefficients and ZT value at the heat source temperature of 325 K. The values are -289.46 μV/K and 1.69, respectively. The value of ZT is improved by about 2 times, compared with Bismuth telluride Bi<sub>2</sub>Te<sub>3</sub> thermoelectric materials.

Flexible thermoelectric composite materials with self-healing ability for harvesting low-grade thermal energy

Directly converting waste heat from environment or human body into electricity without any moving parts is crucial in low-grade waste heat harvesting and wearable electronic applications. In this work, a sunlight self-healing thermoelectric generator that harvests energy from the human body is reported. Self-healing polyurethane gives the thermoelectric generators self-healing capacity, and the p/n-type thermoelectric component is composed of an organic-inorganic composite including carbon nanotubes and semiconductor nanoparticles. The ternary thermoelectric composite film exhibits a largely improved thermoelectric performance compared to the single component due to the energy-level configuration and interfacial energy filtering effect, and the power factor of self-healing p-type composite film is up to 355.6 ± 4.8 μW/(m·K2). Moreover, the healing efficiencies of the thermoelectric performance are both higher than 85% for the self-healing p-type and n-type composite films. The film-shaped thermoelectric generator, which is made up of 5 pairs of p/n-type counterparts, finally produces a voltage of 19.1 mV and power of 0.6 μW at a temperature difference of 60 K. Furthermore, a fibrous thermoelectric generator is also created and it produces a 2.1 mV open-circuit voltage and 1.39 nW power at a temperature difference between a human palm and the ambient environment.

Effects of selenium addition in nanostructured tellurium/PEDOT:PSS thermoelectric composite materials on the improvement of oxidation stability

Recently, the development of a composite thermoelectric material including conducting polymer (PEDOT:PSS) and nanostructured tellurium (Te) offers both high thermoelectric performance and mechanical flexibility. But they are usually vulnerable to oxidation, which limits the material's ability to continuously harvest energy in any environment. To address this issue, this report presents a Se doping strategy to improve the oxidation stability of the composite material, and evaluates the material characteristics and thermoelectric properties of synthesized composites. Se-doped nanostructured Te/PEDOT:PSS composite materials have improved oxidation stability and thermoelectric properties, making them a promising candidate for the next-generation thermoelectric device application.

Recent Advances in Multicomponent Organic Composite Thermoelectric Materials

AbstractOrganic thermoelectric materials have the potential to be used as power supplies for wearable electronics, implantable medical devices, and sensors in Internet of Things. The past 10 years has witnessed the rapid development of the research on organic thermoelectric materials, different material systems and optimizing strategies are developed, and the ZT values of some organic materials have approached that of many inorganic thermoelectric material systems in the low‐temperature region. Among different material systems, organic composite materials, especially multicomponent organic composite materials show very promising thermoelectric properties and offer more tunability compared to single component thermoelectric materials. Multicomponent organic composite thermoelectric materials can not only further improve the ZT values, but also have unique advantages of combining the merits of different materials, thus rendering the composites with better processing, mechanical, or other properties on demand. This review summarizes the concepts, the design criteria, the research progress of organic–inorganic and all‐organic multicomponent thermoelectric materials which contain three or more different ingredients, as well as their applications. Furthermore, the challenges and prospects are also analyzed to provide guidelines for the development of multicomponent organic composite thermoelectric materials.

Flexible pressure/temperature sensing system based on Te-PEDOT:PSS composite thermoelectric material

<p indent="0mm">With the rapid development of artificial intelligence, the demand for new flexible tactile sensors for human-machine interaction technology is increasing sharply. As an essential medium for intelligent bionic systems to obtain external information, such as intelligent manipulators and bionic prosthetic hands, flexible tactile sensors are significant for realizing bionic tactile perception and improving system intelligence. Recently, fabricating multimodal tactile sensors through theoptimal design of functional material and structure has become a key challenge in the field of flexible electronics. Herein, a thermoelectric sensing material composited of Te-poly (3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid) (Te-PEDOT:PSS) was prepared via a hydrothermal method, which was compounded within a three-dimensional porous dense amine foam framework and subsequently coated by a thin polyvinyl alcohol layer for encapsulation. The controllable preparation of sensitive composite materials with high interfacial stability was realized. Thus, the assembled flexible tactile sensor with a thermoelectric effect and capacitance performance can achieve the perception ability of pressure/temperature in contact/noncontact mode, respectively. Further, an intelligent manipulator sensory feedback system is constructed, and its performance in tactile perception is explored.

N-type silver ammonia-polyethyleneimine/single-walled carbon nanotube composite films with enhanced thermoelectric properties.

Carbon nanotubes and their composite thermoelectric (TE) materials have significant advantages in supplying power to flexible electronics due to their high electrical conductivity, excellent flexibility, and facile preparation technology. In this work, stable n-type silver ammonia-polyethyleneimine/single-walled carbon nanotube ([Ag(NH3)2]+-PEI/SWCNT) composite films were facilely prepared by solution blending and vacuum-filtration methods. The results demonstrate that light silver ammonia doping optimizes the carrier concentration and carrier mobility of the composite film, and a maximum power factor (PF) of [Ag(NH3)2]+-PEI/SWCNT of 91.9 μW m-1 K-2 was obtained, which is higher than that of PEI/SWCNT (70.0 μW m-1 K-2). Furthermore, when the composite films were reduced by the NaBH4 solution, the Seebeck coefficient and the PF value were further increased to -45.5 μV K-1 and 115.8 μW m-1 K-2, respectively. For demonstration, a maximum output voltage of 13.8 mV and output power of 492 nW were achieved using a three p-n junction-based TE device constructed by [Ag(NH3)2]+-PEI/SWCNT at a temperature difference of 50 K. Thus, this study provides a metal complex ion doping strategy to improve thermoelectrical properties and air stability of the PEI/SWCNT composite films, which have potential applications in flexible electronics.

Enhanced thermoelectric power factor in the Cu2Se system by the incorporation of GO/MWCNT

The current study examines the transport capabilities of the thermoelectric material of copper selenide (Cu2Se), and its GO (Graphene oxide)/MWCNT (Multi-Walled Carbon Nano Tubes) nanocomposites synthesized using a cost-effective and straightforward chemical reduction method followed by a simple mechanical grinding process. Raman spectra, Field Emission Scanning Electron Microscopymicrographs, High-Resolution Transmission Electron Microscopy images, and the X- Ray Diffraction peak intensity of the all composites showed the existence of GO/MWCNT in the as-prepared samples. The power factor rose with the addition of GO/MWCNT, reaching maximum values of 881μ W/mK2 and 1120μ W/mK2 at 450 °C for Cu2Se-GO and Cu2Se-MWCNT, respectively. According to the findings, the highest thermopower of the Cu2Se-MWCNT composite was around 90 % greater (almost double) than that of bare Cu2Se. This article outlines an efficient and inexpensive process for producing carbon-related thermoelectric composite materials and a viable technique for increasing the power factor to enhance synergistic thermoelectric performance.

Study on Thermoelectric Property of Te Wire-Based Organic-Inorganic Hybrid Thermoelectric Composites through Electrochemical Process

Energy demand and importance are increasing with the industrial development and the development of high technology in modern society. However, the global supply of energy is facing problems such as fossil energy depletion and environmental pollution, and research and interest in alternative energy are increasing. Among them, research on thermoelectricity is being actively conducted. The thermoelectric characteristics are represented by the Seebeck coefficient, electrical conductivity, and thermal conductivity at the operating temperature. This is expressed as a thermoelectric performance index (ZT). ZT appears in proportion to the electrical conductivity and Seebeck coefficient, and inversely proportional to the thermal conductivity. Thermoelectric materials are divided into inorganic thermoelectric materials and organic thermoelectric materials, both of which have advantages and disadvantages. The inorganic thermoelectric material has high thermoelectric performance, but it is highly toxic and has low electrical conductivity. On the other hand, organic thermoelectric materials have lower performance than inorganic materials they are easy to obtain and have high electrical conductivity. In this study, organic-inorganic hybrid thermoelectric material was studied by combining the advantages of each material.In this study, Te nanowires (NWs) were synthesized at 50 Co by galvanic replacement reaction. We used Si (1 0 0) wafer as substrate of NWs. The substrate was degreased with acetone and ethanol. The solution of cadmium(1M), hydrofluoric acid (HF 51.0%, 4.5M) and tellurium dioxide (TeO2, 2mM). After the reaction, the synthesized Te NWs were washed with deionized water and IPA. The prepared Te NWs reacted with solution (silver nitrate in ethylene glycol) for topotactic reaction. After the reaction, the wires are washed several times with ethanol. The hybrid TE was fabricated by coating PEDOT:PSS on Ag-Te NWs with different ethylene glycol (EG) doping.A composite thermoelectric material was manufactured using Te (inorganic thermoelectric material) and PEDOT:PSS (organic thermoelectric material). Ag-topotactic reaction was conducted to increase the electrical conductivity of NWs. As the EG doping concentration of PEDOT increased, the electrical conductivity because the layer of PEDOT:PSS became thinner and didn’t fill the gap of NWS sufficiently. In conclusion, the Te NWs coated with PEDOT:PSS with 10% EG doping showed the best electrical conductivity and power factor. The more details will be presented. Figure 1

High thermoelectric properties of P-SiGe/Sr0.9La0.1Ti0.9−xZrxNb0.1O3 composite

SrTiO3 is a high temperature thermoelectric material with calcium titanite structure that is environmentally friendly and affordable, but the high thermal conductivity at high temperatures limits its development, so how to maintain high electrical properties while reducing thermal conductivity is the most important problem facing SrTiO3. SiGe and SrTiO3 are both thermoelectric materials in the intermediate and high temperature region and have a lot of commonalities, and it is likely to obtain high thermoelectric properties through the interfacial effect of both, however, there is not any study on the compound regulation of the two. Therefore, in this study, phosphorus (P)-doped SiGe was compounded with Zr, La and Nb co-doped SrTiO3. 3 mol.%SiGe(C)/97 mol.% Sr[Formula: see text]La[Formula: see text]Ti[Formula: see text]Zr[Formula: see text]Nb[Formula: see text]O3(Zr1Si3(C)) obtained by sintering under carbon reducing atmosphere shows a relatively large power factor of and low thermal conductivity of 2.88 Wm[Formula: see text]K[Formula: see text] at 1000 K, achieve a ZT value to 0.42 at 1000 K. This is at a high level in this study of SrTiO3 composite thermoelectric materials and provides a new idea for the subsequent study of composite modulation.

Facile synthesis of hetero-structured Bi2S3/SnS2 composite and its improved thermoelectric properties

In this study, bismuth sulfide/tin (IV) sulfide (Bi2S3/SnS2) heterostructure nanocomposites were fabricated to obtain high-performance thermoelectric composite materials. The Bi2S3/SnS2 composites were prepared via solution mixing using a two-step hydrothermal reactor. First, flower-like-shaped Bi2S3 was prepared, after which the as-synthesized Bi2S3 was decorated with SnS2 nanocomposites. The formation of a unique Bi2S3/SnS2 heterostructure was achieved through a thioacetamide-induced surfactant-assisted reaction process. The thermoelectric power factor of the Bi2S3/SnS2 composites was optimized by controlling their Bi:Sn ratios, and changes in the thermoelectric properties of the composites were investigated by examining the change in their carrier transport properties. The composite achieved a maximum thermoelectric power factor of ~99.7 μW/m·K2 at a Bi:Sn ratio of 1:0.2, which is ~5.1 times larger than that of pristine Bi2S3. This increase in the power factor was ascribed to the fact that the enhanced electrical conductivity outweighs the reduction effect of the Seebeck coefficient. The hetero-structured Bi2S3/SnS2 composite is a promising strategy for realizing high-performance sulfur-based thermoelectric composite materials.

Processing of hybrid shape memory alloy coupled with P(VDF-TrFE) piezoelectric polymer composite for energy harvesting application

Small-scale energy harvesting to power self-powered electronic devices is tremendously increasing. In this context, the ability to combine thermal and mechanical energy harvesting using smart materials deserves more attention for further study. We have presented the feasibility of using P(VDF-TrFE) piezoelectric polymer coupled with NiTi shape memory alloy (SMA) to harvest both mechanical and thermal energy in simple scalable devices. A novel hybrid composite consisting of SMA, and P(VDF-TrFE) has been developed without any complex composites or patterned structures, which couples the piezoelectric effect of the poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) and the shape memory effects of NiTi SMA. We have also fabricated a multi-layer SMA/PEN/P(VDF-TrFE) device using epoxy as an interface and bonding layer. During bending, the P(VDF-TrFE) device with an active area of 3.68 cm2 generated an output voltage of 8 V and an output power of 6.25 µW. When coupled with NiTi SMA to create a hybrid composite thermoelectric material, the device can convert the phase change associated with SMA, and thus thermal energy is converted to mechanical energy and finally into electrical energy. The SMA/P(VDF-TrFE) hybrid composite produced an output voltage of ∼2 V for one cyclic heating and cooling of the device. This is a promising approach for the further development of coupled hybrid energy harvester devices for the powering of small-scale electronic devices such as sensors, MEMS, or biomedical devices.

Recent Advances in 2D Material/Conducting Polymer Composites for Thermoelectric Energy Conversion

AbstractTwo‐dimensional material (2DM)/conducting polymer (CP) composites with excellent electrical transport behavior, functional multidimensional structure, and good flexibility have attracted widespread attention as potential composite thermoelectric (TE) materials in the field of energy conversion. Appropriate preparation strategies determine the interface microstructure of 2DM/CP composites, which would influence the optimization degree of TE performance and practical applications. This review describes the recent progress in preparing advanced 2DM/CP composites by different design strategies for improving TE performance. In addition, some typical 2DM/CP composites applied to TE generators are also presented. Finally, other challenges and opportunities toward high‐performance 2DM/CP composites are discussed, including precise structural regulation, an in‐depth understanding of the interfacial transport mechanism, and the development of practical 2DM/CP‐based flexible TE devices.

In-situ pulse electropolymerization of pyrrole on single-walled carbon nanotubes for thermoelectric composite materials

Electrochemical polymerization has become a powerful tool for constructing high-performance thermoelectric (TE) composite films, and attracted great attention from researchers. To date, however, there has been no report on the in-situ electrochemical polymerization of pyrrole (Py) on single-walled carbon nanotubes (SWCNTs). In this work, we developed a series of high-performance polypyrrole (PPy)/SWCNT composites by the in-situ pyrrole electropolymerization on the pre-fabricated SWCNT membrane electrode, where a pulse galvanostatic electropolymerization (PGEP) technology was adopted to perfect TE performance of the PPy/SWCNT composites via the interface engineering. As a result, the optimized PPy/SWCNT composite film achieved an excellent TE performance, with the largest power factor (PF) of 365.2 ± 9.6 μW m−1 K−2 and the maximum figure of merit (ZT) of 0.203 ± 0.005 at room temperature, which is well beyond the reach of the PPy-based binary TE composite materials reported previously. This work suggested that in-situ pulse electropolymerization would be an effective and feasible strategy for constructing high-performance TE materials, and also opened a new, promising avenue for improving TE materials in the future.

Effect of the Addition of Copper Particles on the Thermoelectric Properties of the Ca3Co4O9 + \u03b4 Ceramics Produced by Two-Step Sintering

Composite thermoelectric materials based on layered calcium cobaltite Ca3Co4O9 + δ doped with copper particles were synthesized by two-step sintering, and their microstructure, and electrotransport and thermoelectric properties were studied. It was determined that the introduction of copper particles into the ceramics improves their sinterability at moderate sintering temperatures (Tsint ≤ 1273 K), leading to a decrease in the porosity of the samples and an increase in their electrical conductivity and power factor, whereas the oxidation of copper to less conductive copper(II) oxide significantly decreases the electrical conductivity and power factor of the ceramics sintered at elevated temperatures (Tsint ≥ 1373 K). The power factor is maximum for the Ca3Co4O9 + δ + 3 wt % Cu ceramic sintered at 1273 K (335 μW/(m K2) at a temperature of 1100 K), which is by a factor of 2.3 higher than the power factor of the base material Ca3Co4O9 + δ with the same thermal history (145 μW/(m K2) at 1100 K) and more than 3 times higher than the power factor of the Ca3Co4O9+δ ceramic synthesized by the conventional solid-phase method.

Investigation for performance enhancement of Ni/TiO&lt;sub&gt;2-x&lt;/sub&gt; composite thermoelectric material by Monte-Carlo finite element method

In this study, we built three-dimensional models for the series, parallel composite, and random, off-diagonal and gradient distribution composite. We investigated the thermoelectric characteristics of Ni/TiO2-x composite thermoelectric materials using Monte-Carlo finite elemental method with the three-dimensional models. In addition, Ni/TiO2-x composite thermoelectric compacts were prepared and the thermoelectric properties were measured. We also discussed the influence of the composite structure type on thermoelectric properties for enhancing thermoelectric performance.

Facile fabrication of highly flexible, porous PEDOT:PSS/SWCNTs films for thermoelectric applications

High-performance organic composite thermoelectric (TE) materials are considered as a promising alternative for harvesting heat energy. Herein, composite films of poly (3,4-ethyienedioxythiophene):poly(styrene sulfonate)/single-walled carbon nanotubes (PEDOT:PSS/SWCNTs) were fabricated by utilizing a convenient solution mixing method. Thereafter, the as-prepared hybrid films were treated using sulfuric acid (H2SO4) to further optimize the TE performance. Film morphological studies revealed that the sulfuric acid treated PEDOT:PSS/SWCNTs composite samples all possessed porous structures. Due to the successful fabrication of highly conductive networks, the porous nano-architecture also exhibited much more excellent TE properties when compared with the dense structure of the pristine samples. For the post-treated sample, a high power factor of 156.43 μW⋅m−1⋅K–2 can be achieved by adjusting the content of CNTs, which is approximately 3 orders of magnitude higher than that of the corresponding untreated samples (0.23 μW⋅m−1⋅K–2). Besides, the obtained films also showed excellent mechanical flexibility, owing to the porous nanostructure and the strong π–π interactions between the two components. This work indicates that the H2SO4 treatment could be a promising strategy for fabricating highly-flexible and porous PEDOT:PSS/SWCNTs films with high TE performances.

Synthesis and characterization of G/TiO1.80 bulk composite thermoelectric material under high temperature and high pressure

The primary purpose of this work is to introduce the second phase of graphene (G) into non-stoichiometric TiO1.80 successfully and optimize the thermoelectric properties of this composite material through high pressure and high temperature (HPHT) technology. The purpose of doping Ti powder under high pressure is to create a closed reducing atmosphere to change the ratio of titanium to oxygen in the titanium oxide base. The addition of graphene can considerably improve the electrical properties of the material and reduce its resistivity. An X-ray diffractometer, X-ray photoelectron spectrometer, scanning electron microscope, and transmission electron microscope were used to analyze and characterize the phase structure, chemical bond, micro morphology and crystal morphology of the samples. An abundance of grain boundaries and lattice dislocation defects can inhibit the lattice thermal conductivity. We also tested and analyzed the thermoelectric performance of the high-temperature and high-pressure synthetic samples through a variable temperature system. The variation of the absorption intensity of the ultraviolet UV spectrum with wavelength shows that high pressure can reduce the band gap, which is beneficial to the carrier transition and improves the conductivity of semiconductors. HPHT optimizes both the electrical and the thermal parameters of the sample. At a final sintering pressure of 5.0 GPa, the dimensionless figure of merit (zT) of the bulk composite material G/TiO1.80 was found to be 0.23 at 700 °C.