Nanocomposite Thermoelectric Materials Research Articles

Concentration polarization and ionic conductivity of nanocomposite thermoelectric materials K0.01Cu1.94S, K0.02Cu1.94S, K0.03Cu1.94S

Concentration polarization and ionic conductivity of nanocomposite thermoelectric materials K0.01Cu1.94S, K0.02Cu1.94S, K0.03Cu1.94S

Boosting the thermoelectric performance of n-type Bi2S3 by compositing rGO

The construction of nanocomposite structures can effectively reduce the lattice thermal conductivity of thermoelectric materials, which are considered an essential technique to improve the thermoelectric figure of merit of thermoelectric materials. Herein, we prepared a series of Bi2S3 +xml reduced graphene oxide (rGO)(x = 5 ml, 10 ml, 15 ml, 20 ml) nanocomposite thermoelectric materials by combining simple hydrothermal synthesis techniques and tubular sintering techniques. The rGO is uniformly dispersed in the precursor solution and tightly bound in the Bi2S3 matrix, which significantly reduces the thermal conductivity of the matrix material. The total thermal conductivity(κ) of the Bi2S3/rGO (20 ml) nanocomposite is as low as 0.12 W·K−1·m−1 at 578 K, which is nearly 69% lower than that of the pure Bi2S3. In addition, the conductivity of Bi2S3/rGO (10 ml) nanocomposites above 450 K is better than that of the pure Bi2S3, which indicates that adjusting the content of rGO can optimize the conductivity of Bi2S3 to a certain extent. At 577 K, the ZT of Bi2S3/rGO (10 ml) nanocomposite can reach 0.22, which is 46% higher than that of pure Bi2S3. This study utilizes hydrothermal synthesis techniques and tubular sintering techniques to tune the structure of composites at the nanoscale, providing a new approach for optimizing the thermoelectric properties of Bi2S3.

(Bi2Te3)1−x(PANI)x compositions- synthesis, structural, spectroscopic characterization with enhanced thermoelectric performance

The coupling between semiconductor/ polymer compositions is one of the unique trials to attain outstanding nanocomposite thermoelectric materials. Herein, Bi2Te3/PANI composites prove their ability to achieve the physical properties of the thermoelectrics by the variation of stoichiometric concentrations. The in-situ polymerization method was utilized to obtain Bi2Te3/PANI compositions. The structural characteristics of the materials were investigated by X-ray diffraction (XRD). XRD, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) confirm the homogeneous growth of PANI over the surface of Bi2Te3 nanoparticles, affect on the order structure with low crystallinity during the polymerization. Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) analyses illustrate the π-π interactions of uniform PANI on Bi2Te3 nanoparticles. The other strong interactions, including electrostatic and hydrogen bonding between Bi2Te3 and PANI may construct a route to enhance the order of the structure of the chains and improve the thermoelectric performance. Distinctive revolutionize the electrical resistivity, Seebeck Coefficient, and the power factor with increased PANI concentrations, which improves thermoelectric performance. The spin concentration charge carriers were determined from Electron Spin Resonance (ESR) dependent on the PANI doping levels. The formation of polarons and bi-polarons were produced during the doping process represent the carriers in these systems.

Paper-based thermoelectric generator based on multi-walled carbon nanotube/carboxylated nanocellulose

Cellulose is the most abundant polymer material in nature. After being produced on the nanometer scale, it is widely used in research on flexible energy storage equipment and power supply equipment. Therefore, this study has prepared a nanocomposite thermoelectric material based on multi-walled carbon nanotube (MWCNT) and carboxylated nanocellulose fiber (C-CNF) and obtained a free-standing paper-based thermoelectric generator (TEG) through a simple printing method. The equipment exhibits excellent mechanical flexibility. At the same time, the thermal conductivity is significantly reduced under the dual effects of paper and C-CNF (is reduced to 0.02–0.09 W/mK). The TEG prototype has four P-shaped feet. Under a temperature gradient of 70 K, the open circuit voltage is 3.3 mV, and the output power is up to 3.7 nW. This work not only confirms the improvement of MWCNT thermoelectric performance by C-CNF but also provides a new strategy for the preparation of low-cost and environmentally friendly thermoelectric generators.

Effects of Ni Magnetic Nanoparticles on Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 Materials

A series of n-type x%Ni/Bi2Te2.7Se0.3 (x = 0, 0.1, 0.4, 0.7, and 1.0) magnetic nanocomposite thermoelectric materials have been fabricated by the combination of ultrasonic dispersion, hydrothermal homogenization, and spark plasma sintering. X-ray diffraction analysis indicated that the Ni nanoparticles were unstable in the Bi2Te2.7Se0.3 matrix and prone to react with Te to form NiTe2 phase. Room-temperature charge transport measurements indicated that the conduction behavior of the x%Ni/Bi2Te2.7Se0.3 magnetic nanocomposite changed from n-type (electrons) to p-type (holes) with increasing Ni content, due to the formation of a p-type region in the Bi2Te2.7Se0.3 matrix by the reaction of Ni with Te during the sintering process. The reaction of Ni nanoparticles with Te seriously degraded the electrical and thermal transport properties of the Bi2Te2.7Se0.3 matrix, suggesting that much higher thermoelectric properties could be obtained if an appropriate sintering method which can suppress this reaction were adopted.

Preparation and Thermoelectric Performance of BaTiO3/Bi0.5Sb1.5Te3 Composite Materials

A series of xBaTiO3/Bi0.5Sb1.5Te3 (xBTO/BST) nanocomposite thermoelectric materials were prepared by the method of ultrasonic dispersion combined spark plasma sintering. The thermoelectric performance was systematically investigated in the temperature range from 300 K to 500 K. Combined with the analysis of phase composition and microstructure, the results indicated that the BTO nanoparticles were uniformly dispersed in the grain boundaries of the BST matrix, which can optimize carrier concentration and produce an energy filtering effect to a certain extent to improve the Seebeck coefficient, and also reduced the thermal conductivity. The highest ZT value of the sample with x = 0.2% was achieved 1.2 at 340 K, which was 20% larger than that of the matrix. This work is helpful for exploring new composite systems to improve the thermoelectric performance of composites.

Candidate for Magnetic Doping Agent and High-Temperature Thermoelectric Performance Enhancer: Hard Magnetic M-type BaFe12O19 Nanometer Suspension.

How to prevent the agglomeration of nanoparticles in nanocomposites remains a key challenge. Using nanometer suspension as a doping agent provides an effective approach to solve this challenge. A new technique that consists of chemical coprecipitation, ball milling and sedimentation separation metheds was developed for preparing hard magnetic M-type BaFe12O19 nanometer suspension. The single-phase BaFe12O19 nanoparticles dispersed uniformly in alcohol have been prepared by this new technique. Magnetic nanocomposite thermoelectric materials with a homogeneous dispersion of BaFe12O19 nanoparticles were prepared through a combination process of an ultrasonic mixing of BaFe12O19 nanometer suspension and In-filled CoSb3 thermoelectric matrix material and spark plasma sintering. The microstructure analysis of magnetic nanocomposite thermoelectric materials confirmed that using the nanometer suspension as a doping agent is an effective way to solve the agglomeration phenomenon of nanoparticles in nanocomposites. In addition, the decline of thermoelectric performance in the high-temperature intrinsic excitation region of In-filled CoSb3 can be effectively suppressed by the magnetic phase transition of BaFe12O19 nanoparticles dried by nanometer suspension from ferromagnetism to paramagnetism. It is also confirmed that using the BaFe12O19 nanometer suspension as a thermoelectric performance enhancer is an effective way to solve the challenging problem of performance deterioration of thermoelectric materials at high temperature.

Thermoelectric generators for wearable body heat harvesting: Material and device concurrent optimization

Body heat harvesting systems based on thermoelectric generators (TEGs) can play a significant role in wearable electronics intended for continuous, long-term health monitoring. However, to date, the harvested power density from the body using TEGs is limited to a few micro-watts per square centimeter, which is not sufficient to turn on many wearables. The thermoelectric materials research has been mainly focused on enhancing the single parameter zT, which is insufficient to meet the requirements for wearable applications. To develop TEGs that work effectively in wearable devices, one has to consider the material, device, and system requirements concurrently. Due to the lack of an efficient heatsink and the skin thermal resistance, a key challenge to achieving this goal is to design systems that maximize the temperature differential across the TEG while not compromising the body comfort. This requires favoring approaches that deliver the largest possible device thermal resistance relative to the external parasitic resistances. Therefore, materials with low thermal conductivity are critically important to maximize the temperature gradient. Also, to achieve a high boost converter efficiency, wearable TEGs need to have the highest possible output voltage, which calls for a high Seebeck coefficient. At the device level, dimensions of the legs (length versus the base area) and fill factor are both critical parameters to ensure that the parasitic thermal resistances are again negligible compared to the resistance of the module itself. In this study, the concurrent impact of material and device parameters on the efficiency of wearable TEGs is considered. Nanocomposite thermoelectric materials based on bismuth telluride alloys were synthesized using microwave processing and optimized to meet the requirements of wearable TEGs. Microwave energy decrystallized the material leading to a strong reduction of the thermal conductivity while maintaining a high zT at the body temperature. A comprehensive quasi-3D analytical model was developed and used to optimize the material and device parameters. The nanocomposite TEG produced 44 μW/cm2 under no air flow condition, and 156.5 μW/cm2 under airflow. In comparison to commercial TEGs tested under similar conditions, the nanocomposite based TEGs exhibited 4–7 times higher power density on the human body depending on the convective cooling conditions.

New free-standing and flexible PVA/Carbon quantum dots (CQDs) nanocomposite films with promising power factor and thermoelectric power applications

Recently, flexible nanocomposite thermoelectric materials, especially inorganic polymers, have attracted increasing attention. In this paper, we successfully fabricated novel P-type thermoelectric PVA/CQDs nanocomposite films through the solution casting technique. Zero-dimension CQDs nanoparticles were first prepared by the microwave heating method and then injected into the PVA matrix to achieve free-standing films. PVA/CQDs nanocomposite films were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermoelectric properties such as electrical conductivity, Seebeck coefficient, and thermal conductivity of the prepared films were studied. XRD patterns showed the effect of CQDs nanoparticles on the crystallinity of the nanocomposite. The average size of CQDs nanoparticles was found to be 4.5 nm. The PVA/CQDs nanocomposite has a high conductivity (30.3 S/cm), an excellent power factor (15.2 μW/m K2), and a high figure of merit (0.005) with CQDs content of 2 wt%. Finally, these nanocomposites have a promising potential application in thermoelectric devices because they are economical and easy to scale up.

Progress on PEDOT:PSS/Nanocrystal Thermoelectric Composites

AbstractIn recent years, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐based nanocomposite thermoelectric (TE) materials are extensively investigated since they can take the advantages of both PEDOT:PSS (e.g., low thermal conductivity, high electrical conductivity, solution processability, and flexibility) and inorganic nanocrystals (e.g., high Seebeck Coefficient) to yield TE performance comparable to that of traditional inorganic TE materials. Besides, various preparation processes allow the mass fabrication of PEDOT:PSS‐based TE materials using some time‐saving and cost‐effective technologies, such as roll‐to‐roll and screen printing methods. This review focuses on the recent progress of PEDOT:PSS/inorganic nanocrystal composites for TE application. The relevant preparation strategies and TE properties are discussed intensively. In addition, the fabrication method, synergistic effect, and energy filtering effect involved in the composites, and flexible devices assembled from the composites are also discussed. Finally, challenges and prospects for future studies are summarized.

Effects of Fe3O4 Magnetic Nanoparticles on the Thermoelectric Properties of Heavy-Fermion YbAl3 Materials

The magnetic nanocomposite thermoelectric materials xFe3O4/YbAl3 (x = 0%, 0.3%, 0.6%, 1.0%, and 1.5%) have been prepared by the combination of ultrasonic dispersion and spark plasma sintering process. The nanocomposites retain good chemical stability in the presence of the second-phase Fe3O4. The second-phase Fe3O4 magnetic nanoparticles are distributed on the interfaces and boundaries of the matrix. The x dependences of thermoelectric properties indicate that Fe3O4 magnetic nanoparticles can significantly decrease the thermal conductivity and electrical conductivity. The magnetic nanoparticles embedded in YbAl3 matrix are not only the phonon scattering centers of nanostructures, but also the electron scattering centers due to the Kondo-like effect between the magnetic moment of Fe3O4 nanoparticles and the spin of electrons. The ZT values of the composites are first increased in the x range 0%–1.0% and then decreased when x > 1.0%. The highest ZT value reaches 0.3 at 300 K for the nanocomposite with x = 1.0%. Our work demonstrates that the Fe3O4 magnetic nanoparticles can greatly increase the thermoelectric performance of heavy-fermion YbAl3 thermoelectric materials through simultaneously scattering electrons and phonons.

Thermoelectric Transport in Nanocomposites.

Thermoelectric materials which can convert energies directly between heat and electricity are used for solid state cooling and power generation. There is a big challenge to improve the efficiency of energy conversion which can be characterized by the figure of merit (ZT). In the past two decades, the introduction of nanostructures into bulk materials was believed to possibly enhance ZT. Nanocomposites is one kind of nanostructured material system which includes nanoconstituents in a matrix material or is a mixture of different nanoconstituents. Recently, nanocomposites have been theoretically proposed and experimentally synthesized to be high efficiency thermoelectric materials by reducing the lattice thermal conductivity due to phonon-interface scattering and enhancing the electronic performance due to manipulation of electron scattering and band structures. In this review, we summarize the latest progress in both theoretical and experimental works in the field of nanocomposite thermoelectric materials. In particular, we present various models of both phonon transport and electron transport in various nanocomposites established in the last few years. The phonon-interface scattering, low-energy electrical carrier filtering effect, and miniband formation, etc., in nanocomposites are discussed.

Increased power factors of organic–inorganic nanocomposite thermoelectric materials and the role of energy filtering

Enhancements in the performance of organic–inorganic nanocomposite thermoelectrics may be obtained with both small and large energy barriers at the organic–inorganic interfaces.

Magnetoelectric interaction and transport behaviours in magnetic nanocomposite thermoelectric materials.

How to suppress the performance deterioration of thermoelectric materials in the intrinsic excitation region remains a key challenge. The magnetic transition of permanent magnet nanoparticles from ferromagnetism to paramagnetism provides an effective approach to finding the solution to this challenge. Here, we have designed and prepared magnetic nanocomposite thermoelectric materials consisting of BaFe12O19 nanoparticles and Ba0.3In0.3Co4Sb12 matrix. It was found that the electrical transport behaviours of the nanocomposites are controlled by the magnetic transition of BaFe12O19 nanoparticles from ferromagnetism to paramagnetism. BaFe12O19 nanoparticles trap electrons below the Curie temperature (TC) and release the trapped electrons above the TC, playing an 'electron repository' role in maintaining high figure of merit ZT. BaFe12O19 nanoparticles produce two types of magnetoelectric effect-electron spiral motion and magnon-drag thermopower-as well as enhancing phonon scattering. Our work demonstrates that the performance deterioration of thermoelectric materials in the intrinsic excitation region can be suppressed through the magnetic transition of permanent magnet nanoparticles.

Prospects of creating efficient thermoelectric materials based on the achievements of nanotechnology

The elaboration of low-dimensional thermoelectric structures has been shown to allow an increase in the efficiency of thermoelectric materials by the end of the 20th century. The achievements in nanotechnology open up new opportunities in searching for prospective thermoelectric materials and structures. The physical aspects in the creation of low-dimensional thermoelectric structures have been reviewed. The capabilities of developing technologies for the synthesis of thermoelectric structures on the basis of superlattices, quantum wires, and quantum dots have been analyzed. The methods of fabrication and advances in the elaboration of nanocomposite thermoelectric materials have been discussed. The problems in the production of second-generation nanocomposites and their possible solutions have been considered. The methods for diagnosing low-dimensional thermoelectric structures are presented, as well.

Analytical and Numerical Studies of Heat Transfer in Nanocomposite Thermoelectric Coolers

Thermoelectric coolers (TEC) can produce a cooling effect (in refrigerator mode) or a heating effect (in heat pump mode) using electrical energy input. Performance characteristics of typical TECs are poor when compared to the traditional cooling system (e.g., a vapor compression system). However, nanostructuring of thermoelectric (TE) materials can generate high-performance TE materials (e.g., high Seebeck coefficient, low thermal conductivity, and high electrical conductivity), and such materials show the promise to improve the performance of TEC. The main objective of this paper is to investigate the effect of nanocomposite TE materials and surface to surrounding convection heat transfer on the thermal performance of TEC. The mathematical model developed in this paper includes Fourier heat conduction, Joule heat, Seebeck effect, Peltier effect, and Thomson effect. This model also includes temperature-dependent transport properties. Governing transport equations are solved numerically using the finite element method to identify temperature and electrical potential distributions and to calculate heat absorbed and the coefficient of performance (COP). Heat absorbed and COP are also calculated using a simplified 1D analytical solution and compared with numerically obtained results. An optimum electric current is also calculated for maximum heat absorption rate and maximum COP for fixed geometric dimensions and variable convection heat transfer coefficients. An Increase in the convection heat transfer coefficient increases the optimum electric current required for maximum heat absorption rate and maximum COP. For the materials considered, the results show that COP of TEC can be increased by approximately 13 ± 1% if nanostructured TE materials are used instead of the conventional TE materials.

Enhanced power factor and reduced thermal conductivity of a half-Heusler derivative Ti9Ni7Sn8: A bulk nanocomposite thermoelectric material

We report a half-Heusler (HH) derivative Ti9Ni7Sn8 with VEC = 17.25 to investigate the structural changes for the optimization of high thermoelectric performance. The structural analysis reveals that the resulting material is a nanocomposite of HH and full-Heusler with traces of Ti6Sn5 type-phase. Interestingly, present nanocomposite exhibits a significant decrease in thermal conductivity due to phonon scattering and improvement in the power factor due to combined effect of nanoinclusion-induced electron injection and electron scattering at interfaces, leading to a boost in the ZT value to 0.32 at 773 K, which is 60% higher than its bulk counterpart HH TiNiSn.

Transport properties of nanocomposite thermoelectric materials based on Si and Ge

The modification of transport properties (thermal conductivity, electrical conductivity, and See-beck coefficient) of nanostructured thermoelectrics based on Ge and Si-Ge with inclusions of the second phase has been investigated experimentally. In the Ge-C60 nanocomposite, modifying inclusions are the fullerene C60 located along the germanium grain boundaries and 1- to 5-nm SiC nanocrystals in the Si-Ge-SiC nanocomposite. In particular, the presence of these inclusions in the nanocomposite leads to an increase of the Seebeck coefficient in the temperature range above 600 K and, in general, to an increase in the thermoelectric figure of merit ZT by a factor of 1.5–2 as compared to the corresponding characteristics of nanostructured thermoelectrics based on Si-Ge without modifying inclusions of the second phase.

Characterization of nanoembedded alloyed thermoelectrics

Nano-structured alloyed materials have been demonstrated with a large improvement of their thermoelectric properties. These improvements have been obtained by tailoring a reduction in the material thermal conductivity. However, such improvements have not yet been demonstrated for bulk materials. Recently, a new approach based on phonon scattering theory has been successfully applied to bulk materials. In this approach, nanoparticles are embedded in a hosting matrix and act as multi-scale phonon scattering centres providing a reduction in the material thermal conductivity. In this work, {CoSi2 (nanoparticle): SiGe (host)} nanocomposite thermoelectric materials and their precursors for the synthesis were investigated. The purpose of the investigation is to understand the inherent interactions of the nanoparticles with the support material.

Low Thermal Conductivity in High-Z Thermoelectric Materials with Controlled Nanodispersions

We report wet chemical synthesis of a hierarchical nanocomposite thermoelectric material, (Bi,Sb)2Te3 + 2 vol.% Sb2O3, which exhibits a very high ZT value of 1.5 at 333 K. The key to such a high ZT value is to design the interfacial density (ID) of the nanodispersion and the mean diameter of the matrix (d) in the nanocomposite. To this end, (Bi,Sb)2Te3 with Sb2O3 nanodispersion was developed using in situ precipitation during solvothermal treatment. Nanocomposite structure was observed in sintered specimens. By evaluation of thermoelectric properties, it was confirmed that phonon scattering on the surface of Sb2O3 dispersion and κph correspondingly decreased with ID. The formation of a well-controlled Sb2O3 dispersion (mean diameter of dispersion: D = 1.5 nm, ID = 0.06 nm−1) and fine grains (d = 38 nm) led to an extremely low lattice thermal conductivity of 0.28 W m−1 K−1, while reducing the electrical conductivity moderately according to the conventional mixture rule.