Materials For Thermoelectric Generators Research Articles

Production and development of ZnAlGeO semiconducting materials for thermoelectric generators in potential aerospace applications

Production and development of ZnAlGeO semiconducting materials for thermoelectric generators in potential aerospace applications

Production of ZnAlO semiconducting materials for thermoelectric generators in potential aerospace applications

Production of ZnAlO semiconducting materials for thermoelectric generators in potential aerospace applications

A Review of Thermoelectric Generators in Automobile Waste Heat Recovery Systems for Improving Energy Utilization

With the progress of modern times, automobile technology has become integral to human society. At the same time, the need for energy has also grown. In parallel, the total amount of waste energy that is liberated from different parts of the automobile has also increased. In this ever-increasing energy demand pool, future energy shortages and environmental pollution are the primary concerns. A thermoelectric generator (TEG) is a promising technology that utilizes waste heat and converts it into useful electrical power, which can reduce fuel consumption to a significant extent. This paper comprehensively reviews automobile thermoelectric generators and their technological advancements. The review begins by classifying different waste heat technologies and discussing the superiority of TEGs over the other existing technologies. Then, we demonstrate the basic concept of and advancements in new high-performance TEG materials. Following that, improvements and associated challenges with various aspects, such as the heat exchanger design, including metal foam, extended body, intermediate fluid and heat pipe, leg geometry design, segmentation, and multi-staging, are discussed extensively. Finally, the present study highlights research guidelines for TEG design, research gaps, and future directions for innovative works in automobile TEG technologies.

Analysis of the problems of synthesis of new nanocrystalline chalcogenide materials for thermoelectric generators and sodium-ion batteries

The paper analyzes the problems of the synthesis of new nanocrystalline chalcogenide materials for thermoelectric generators and sodium-ion batteries. The objectives of the synthesis will determine the best method to use to create chalcogenide materials for electrodes in real-world applications. The method of direct solid-phase reaction in a vacuum or in an environment of pure inert gas is the most effective way to generate novel chalcogenide materials in tiny amounts for the investigation of physicochemical and other features.With this approach, which is more dependable, it is feasible to produce a pure result free of contaminants that are inescapable when working with other solvents and precursors. Additionally, in a consistent synthesis regime, it is differentiated by the stability of the acquired attributes of the compounds. Synthesis modes, reagents, and post-processing depend on the specific material. The method of synthesizing alloys in a melt media made up of a combination of potassium and sodium hydroxides is one of the key techniques employed in the present research. The melting point drops to 165 °C at a certain ratio of the concentrations of these hydroxides, allowing for the execution of salt exchange processes in the melt. The size of the resultant chalcogenide particles can be reduced to a few nanometers by lowering the synthesis temperature, adding water, and shortening the annealing period.

Study of spin control on half metallic ferromagnetism and thermoelectric properties of MgEu2(S/Se)4 for spintronic and energy harvesting devices

Spintronic is the emerging technology for next generation electronic devices that can improve memory and computing capability by use of electrons spin degree of freedom. The electronic, magnetic, and transport properties of MgEu2(S/Se)4 spinels are explored systematically. These spinels are stable in ferromagnetic state (FM) confirmed by energy release in optimization, phonons band structures, and enthalpy of formation (ΔHf). The Curie temperature and spin polarization signify spin polarization at high temperature. The hybridization of p-S/Se and f-Eu states have been discussed from Band structure, and density of states which explain the nature of ferromagnetism. The crystal field and exchange energies are also reported for the verification of control of electrons spin. Furthermore, the exchange constants, and double exchange mechanism also premeditated. The double exchange model is satisfied by the negative Δx (pf) and constant Noβ. Moreover, the Seebeck coefficient, conductivities, and power factor (PF) for spin (↑) and spin (↓) are investigated separately and collectively by BoltzTraP code. The high values of PF and ultralow values of thermal conductivity make the potential materials for thermoelectric generators.

Recent Developments in Thermoelectric Generation: A Review

The world’s growing energy demand poses several concerns regarding the rational and efficient use of energy resources. This is also the case for many industrial processes, where energy losses and particularly thermal losses are common. Thermoelectric generators offer an alternative to address some of these challenges by recovering wasted heat and thereby increasing the overall efficiency of these processes. However, the successful operation of the thermoelectrical modules meant to carry this process is only possible when pairing these to an external control system; such a system plays an important role in predicting and operating such modules at its maximum power point. In this review paper, recent developments in the field of thermoelectric technology are discussed along with their mathematical models, applications, materials, and auxiliary devices to harvest thermal energy. Moreover, new advancements in phenomenological models are also discussed and summarized. The compiled evidence shows that the thermal dependence properties on the thermoelectric generator material’s modules and the mismatching thermal conditions play an important role in predicting power output in those systems, which prove the importance of including those parameters to enhance the accuracy of the energy production prediction. In addition, based on the evaluation of the mathematical models, it is shown that more studies are required to fill the gap between the current state-of-the-art of the technology and adjacent modeling techniques for the design and evaluation of thermal energy harvesting systems employing thermoelectric arrays under mismatching thermal conditions.

Comparison of thermoelectric properties of sorted and unsorted semiconducting single-walled carbon nanotube free-standing sheets

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are promising materials for thermoelectric generation (TEG) because of their large theoretical Seebeck coefficient (S). In this study, to discuss superiority of s-SWCNTs for TEG devices, thermoelectric properties of free-standing s-SWCNT sheets were compared with unsorted SWCNT sheets. To obtain the highest power density, the films were doped with triethyloxonium hexachloroantimonate and 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole as the hole and electron dopants, respectively. The doped s-SWCNT sheets exhibited higher S but lower electrical conductivity than those of the unsorted SWCNT sheets. Consequently, the power factor of the s-SWCNT sheets was lower than that of the unsorted SWCNT sheets.

The role of phonon anharmonicity on the structural stability and phonon heat transport of CrFeCoNiCux high-entropy alloys at finite temperatures

Chemical disorder and lattice distortion make high-entropy alloys (HEAs) promising to become a new generation of thermoelectric materials. However, the large parameter space of HEAs makes it still a great challenge to study their anharmonic unfolded phonon properties, and the role of anharmonicity in their structural stability and phonon heat transport is still unclear. Here we provide a new scheme to achieve a breakthrough in obtaining the unfolded anharmonic phonon properties from the dynamic trajectories. Through careful analysis of the unfolded phonon dispersions, we found that CrFeCoNiCu HEA has a special anharmonic phonon scattering distribution, which makes the contribution of short-wavelength and long-wavelength phonons to lattice thermal conductivity significantly different. In addition, we have developed a model for estimating the formation energy of HEAs based on the formation energy of binary alloy from first-principles calculation. Our results also show that anharmonic phonon scattering plays an important role in the stability of CrFeCoNiCux HEAs solid-solution phase, which also complements the dynamic mechanism of the formation and stability of dual-FCC phase. CrFeCoNiCu HEA has very low lattice thermal conductivity even at extremely low temperatures. The contribution of long-wavelength phonons to lattice thermal conductivity is more than ten times that of short-wavelength phonons, and they are the main contributors of phonon heat transport of CrFeCoNiCu HEA. This study makes it possible to study the unfolded phonon properties of HEAs at finite temperature and provides important theoretical support and information for the stability of solid-solution structure and phonon engineering for HEAs.

The investigation of natural-rubber for improving self-powered heat detector based on thermoelectric generators

Fire hazard has destroyed humanity creations. Fire detectors have been developed by using different techniques. Thermoelectric generator (TEG) is a part of energy harvesting which is able to convert heat into electricity because of temperature difference between hot and cold side of thermoelectric device (TE). Different materials are used for thermoelectric generators which depend on the characteristics of the heat source, heat sink and the design of the thermoelectric generator. Many thermoelectric generator materials are currently undergoing research. This paper presented an investigation of seeking an alternative way of detecting fire hazard by developing architecture prototype of a fire detection technique using natural rubber. The thermoelectric prototype used self-powered device which improved the temperature difference gap and stabilized the cold side of TE alongside natural rubber as the cooling material. The technique is relatively simple system realization based on three viable components, i.e. a heat sensor, a low-power RF-transmitter and a RF-receiver. The heat sensor is designed and fabricated by thermoelectric and heat sink with natural rubber (NR) coating. The NR coating is heat absorption reduction. Therefore, the temperature difference is wildly resulting in the higher TE output voltage. The voltage is also supplied to the low-power RF transmitter module. In case of fire hazard, the temperature increases from 26 to 100 °C , the prototype can operate successfully. This technique will solve potentially the power supply issue in fluctuated situations. The rubber coating from rubber trees in Thailand would be a value chain added for bio-economy, supporting a sustainable development goal of the country

(Invited) Thermoelectric Properties of Tin-Incorporated Group-IV Thin Films

Integration of a thin-film energy-harvesting device in a silicon (Si) chip strongly desires to realize a standalone sensing network system called the internet-of-things (IoT) society. The thermoelectric generator (TEG), which could convert waste heat into electricity, is one option. Considering many IoT sensors will be distributed worldwide, it is desirable to manufacture them using the same technology as next-generation Si-based integrated circuits, including the material. Tin-incorporated group-IV materials, such as germanium tin (Ge1−x Sn x ) and silicon tin (Si1−x Sn x ), theoretically possess a lower thermal conductivity [1] than those of Ge and Si, respectively, owing to the mass-difference scattering of phonons. Thermoelectric efficiency is inversely proportional to thermal conductivity; hence, the tin-incorporated group-IV thin films are one of the attractive TEG materials. The low thermal conductivity also helps ensure temperature differences within small TEG devices.Against the background, this paper will discuss the thermoelectric properties of the tin-incorporated group-IV thin films grown by low-temperature molecular beam epitaxy. The thermal conductivity of Ge0.95Sn0.05 was reduced down to 2.5 Wm−1K−1 [2] by introducing the stacking faults due to microscopic tilt in the crystals, which value is 4% of bulk-Ge (60 Wm−1K−1 [3]). The stacking faults did not have much adverse effect on carrier conduction, especially for electron conduction. Additionally, relatively high-power factors of ~10 and ~30 μWcm−1K−2 at room temperature (RT) were realized for the p- and n-type Ge1−x Sn x layers, respectively. The power factor for the n-type layers is comparable with the counterpart of the n-type BiTe-based layers (~25 μWcm−1K−2 at RT) [4]. Combined with the recent progress in the polycrystalline layers [5], we will present a guideline for enhancing the power factor in Sn-incorporated group-IV materials. Acknowledgments This work as partly supported by PRESTO (No. JPMJPR15R2) and CREST (No. JPMJCR19Q5) from the JST in Japan, JSPS KAKENHI (Nos. 19K21971, 19H00853, 20H05188, 21H01366), and a research grant (Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development) from the MEXT in Japan.

Electrochemical Approach to Fabricate Semiconducting 2-D Metal-Organic Frameworks Based Thermoelectric Devices

In recent years, there has been special interest in developing devices capable to harvest and store energy from natural resources without the generation of pollution. Thermoelectric generator (TEG) is an emergent technology to harvest energy, especially in those environments in which heat waste is involved. These solid-state devices are capable of generating an output voltage as a function of a temperature difference. The conversion of thermal energy into electrical energy in these devices is attributed to the Seebeck effect. The efficiency of a TEG is evaluated through the dimensionless figure of merit, Z. In order to achieve a competitive the figure of merit, a material with a high Seebeck coefficient, electrical conductivity and low thermal conductivity is desirable.Conductive metal organic frameworks (c-MOFs) are hybrid materials composed of inorganic and organic building blocks, in which metal nodes are coordinated to highly conjugated organic linkers.1,2 The overlap between the metal and ligand frontier orbitals facilitates the charge transport in these materials. Porosity and heterogeneity in atomic species and linkers are features that have led to a predictably low thermal conductivity3, a key aspect to optimize Z, making MOFs potential candidates for TEG. To implement their practical use, the synthesis and study of ultrathin c-MOFs nanosheets have recently been reported4; however, the processing at large scale of these materials is still a challenge.In this work we present an electrochemical approach to the growth of conducting thin films of the 2D c-MOF Cu3(HHTP)2 (where HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene). Bulk Cu3(HHTP)2 was synthesized solvothermally according to the literature5 and we have subsequently fabricated thin films of this important framework by anodic electrochemical synthesis.6 We report the first thermoelectric measurements of this framework both in bulk and thin film form which resulted in Seebeck coefficients of -7.24 μV K-1 and -121.4 μV K-1 with a power factor of 3.15x10-3 μW m-1 for the film respectively. The study of conducting MOFs and their performance as TEG is expected to expand and offer alternatives to non-toxic, scalable and high-efficiency novel TEG materials.[1] P. Q. Liao, J. Q. Shen, J. P. Zhang, Coord. Chem. Rev. 373, 22, 2018[2] L. Sun, M. G. Campbell, M. Dincă, Angew. Chem. Int. 55, 3566, 2016[3] Huang , A. McGaughey , M. Kaviany , Int. J. Heat Mass Transf. 50, 393, 2007[4] W. Zhaoa, et al., Coord. Chem. Rev. 377, 44, 2018[5] M. Hmadeh, et al., Chem. Mater. 24, 3511, 2012[6] Ameloot, R. et al., Chem. Mater. 21, 2580–2582, 2009

Porous Metal-Organic-Framework (MOF) Based Hybrid Materials for Thermoelectric Applications

Thermoelectric materials based on porous hybrid and MOFs constitute a very recent development, with many new and undiscovered phenomena for the research field. These porous Hybrid materials and MOF (Metal-Organic-Framework) films represent modern designer materials that exhibit many requirements of a near ideal and tunable future thermoelectric (TE) material. It is anticipated that especially the inherent porosity can be used advantageously in the design and simulation predictions of future thermoelectric materials. In principle, porous Hybrid and MOFs materials can comply with most of the requirements of an ideal and tunable future thermoelectric (TE) material. In contrast to traditional semiconducting bulk thermoelectric materials, porous hybrid MOF templates can be used to overcome some of the constraints of physics in bulk thermoelectric materials. These porous hybrid systems are amenable for simulation and modeling to design novel optimized electron-crystal phonon-glass materials with potentially very high Figure of Merit (ZT) numbers. Porous MOF and Hybrid materials possess an ultra-low thermal conductivity, which can be further modulated by phonon engineering within their complex porous and hierarchical architecture to advance the thermoelectric figure of merit ZT. This class of novel materials offers new approaches to the design of complex and hierarchical porous structures, possessing ultra-low thermal conductivity, which are able to trap, and localize phonons, thus resulting in a new generation of thermoelectric materials with a high ZT number. This work is demonstrating recent results of MOF thermoelectric Materials and provides a future outlook to the search for the next generation thermoelectric porous Hybrid and MOF materials, which could be part of a green renewable energy revolution with novel materials of sustainable high ZT values.

Electronic origin of the enhanced thermoelectric efficiency of Cu2Se

Thermoelectric materials (TMs) can uniquely convert waste heat into electricity, which provides a potential solution for the global energy crisis that is increasingly severe. Bulk Cu2Se, with ionic conductivity of Cu ions, exhibits a significant enhancement of its thermoelectric figure of merit zT by a factor of ~3 near its structural transition around 400 K. Here, we show a systematic study of the electronic structure of Cu2Se and its temperature evolution using high-resolution angle-resolved photoemission spectroscopy. Upon heating across the structural transition, the electronic states near the corner of the Brillouin zone gradually disappear, while the bands near the centre of Brillouin zone shift abruptly towards high binding energies and develop an energy gap. Interestingly, the observed band reconstruction well reproduces the temperature evolution of the Seebeck coefficient of Cu2Se, providing an electronic origin for the drastic enhancement of the thermoelectric performance near 400 K. The current results not only bridge among structural phase transition, electronic structures and thermoelectric properties in a condensed matter system, but also provide valuable insights into the search and design of new generation of thermoelectric materials.

Non-Rigid Band Structure in Mg2Ge for Improved Thermoelectric Performance.

Magnesium silicide and its solid solutions are among the most attractive materials for thermoelectric generators in the temperature range of 500–800 K. However, while n‐type Mg2(Si,Ge,Sn) materials show excellent thermoelectric performance, the corresponding p‐type solid solutions are still inferior, mainly due to less favorable properties of the valence bands compared to the conduction bands. Here, Li doped Mg2Ge with a thermoelectric figure of merit zT of 0.5 at 700 K is reported, which is four times higher than that of p‐type Mg2Si and double than that of p‐type Mg2Sn. The reason for the excellent properties is an unusual temperature dependence of Seebeck coefficient and electrical conductivity compared to a standard highly doped semiconductor. The properties cannot be captured assuming a rigid band structure but well reproduced assuming two parabolic valence bands with a strong temperature dependent interband separation. According to the analysis, the difference in energy between the two bands decrease with temperature, leading to a band convergence at around 650 K and finally to an inversion of the band positions. The finding of a combination of a light and a heavy band that are non‐rigid with temperature can pave the way for further optimization of p‐type Mg2(Si,Ge,Sn).

Numerical analysis of a variety of thermoelectric generator materials

The generation of electrical energy from thermal energy is often carried out by a large range of capacities of thermal equipments. At present, necessary input for low power device systems particularly sensors, Global Positioning Systems (GPS), Bluetooth receivers is mostly from high power rated device sources. In this scenario, power loss is significant, while converting power from the high power ranges into low power ranges (<1 W). This problem can be mitigated using thermoelectric generators to generate electrical energy from the temperature difference at low power ranges. The thermoelectric generators have compensated by the low-temperature differences for the most important applications of low-power electrical energy. Before generating electrical energy, most existing thermal devices are coupled with mechanical devices (such as shaft). The thermoelectric generator has a lot of advantages including compactness, quietness and, the efficiency with no moving parts. In this article, different types of thermocouples (Type E, K, J, T, and Bi2Te3) are studied to better analyze their parameters of performances. In this study, we have used thermoelectric generator units each consisting of a total of 96 thermocouples. The temperature difference between the hot and cold side area is preserved in the range of 23 K and 191 K. The power generation in different types of thermocouples depends on the Seebeck coefficient and thermal conductivity of each product of the thermoelectric generator. The performances of maximum up to 2072 W and minimum from 243.2 W were observed by both the J-type and Bi2Te3 materials.

An Integrated SiGe Based Thermoelectric Generator with Parabolic Trough Collector Using Nano HTF for Effective Harvesting of Solar Radiant Energy

An integrated thermoelectric generator (TEG) with the parabolic trough collector (PTC) for renewable power generation system has been investigated under different solar irradiations, heat transfer fluids (HTF) and TEG materials. In this research work, the idea of using a TEG for effective heat recovery from a solar collector is implemented in an innovative approach. The heat absorbed from PTC is supplied with the hot junction of the TEG and the cold junction being maintained less than surrounding temperature with cold water using an earthen pot surrounded by a thermocole. The temperature gradient between the hot and cold junction of TEG establishes the amount of power extraction. The high temperature absorption is enhanced by the use of synthetic HTF and nanofluids with nano particles (Alumina, Silica, TiO2 and CuO), which increases the effective harvesting of solar radiant energy. Moreover, the research work focuses to find the most efficient material for the hot and cold part of TEG. Silicon Germanium (SiGe) material for fabrication of TEG is suggested which has good ZT (figure of merit) values and electrical profile as compared to conventional Bismuth Telluride (Bi2Te3) under different solar irradiation conditions has been evaluated. The mathematical modelling of this proposed integrated energy harvesting system has been developed. The modelling and array configuration of TEG has been analysed with conventional Bi2Te3 and proposed SiGe materials. The performance of TEG with a PTC integrated system has been experimentally tested and the obtained results illustrate the better effective harvesting of solar energy for electrical power generation.

Doubling the thermoelectric power factor of earth abundant tin nitride thin films through tuned (311) orientation by magnetron sputtering

Thermoelectricity has been considered a promising green energy source for mankind. This method of energy generation poses challenges due to scarcity of the constituent elements of the efficient thermoelectric materials. The development of high performance materials for thermoelectric generation is limited with the co-responsive nature of transport parameters. In this work, earth abundant tin nitride (Sn3N4) thin films were deposited by reactive radio frequency magnetron sputtering and investigated its thermoelectric response. The electron bands of the prepared thin films were actively aligned to optimize the trade-off between the Seebeck coefficient and electrical conductivity for the enhancement of power factor (S2σ). The reduction in nitrogen gas pressure of reactive sputtering reduced both working pressure and the amount of reactive nitrogen. This experimental approach of combined effect introduced preferred orientation (PO) and stoichiometric variations simultaneously in the fabricated thin films. The increased scattering associated with preferred orientation and increased carrier concentration associated with stoichiometric variations converged the conduction band along with shifting of Fermi energy toward the conduction band minimum. The engineered band structure of tin nitride thin film realized over 2-fold hike in power factor up to 390 μW/m-K2 at 250 °C with a Seebeck coefficient of −144 μV/K and resistivity of 53.11 μΩ-m. This study reveals the potential nature of the earth abundant nitrides in the field of renewable energy generation. The experimental strategy adopted in this study provides an alternative approach to engineer the band structure of a thin film for optimized transport parameters.

Optimizing on thermoelectric elements footprint of the photovoltaic-thermoelectric for maximum power generation

A finite element method (FEM) model for the hybrid PV-TE uni-couple is presented to determine the optimal geometry of the thermoelectric generator (TEG) element for the maximum efficiency. The three-dimensional (3D) governing equations of the thermoelectric for the heat transfer are solved using the FEM based on the temperature dependent properties of TEG materials. The geometric parameters of the TEG were anlyzed in the simulation include the ratio of the area of n- and p-type (An/Ap), the length and the area of the TEG. The result shows that for different areas and different lengths of TEG, the maximum power outputs of the PV-TE all occur with An/Ap = 1 which is different from the TEG solely optimization. This study will provide the valuable reference for PV-TE design.

Thermoelectric power factor of nanocomposite materials from two-dimensional quantum transport simulations

Nanocomposites are promising candidates for the next generation of thermoelectric materials since they exhibit extremely low thermal conductivities as a result of phonon scattering on the boundaries of the various material phases. The nanoinclusions, however, should not degrade the thermoelectric power factor, and ideally should increase it, so that benefits to the ZT figure of merit can be achieved. In this work we employ the nonequilibrium Green's function quantum transport method to calculate the electronic and thermoelectric coefficients of materials embedded with nanoinclusions. For computational effectiveness we consider two-dimensional nanoribbon geometries, however, the method includes the details of geometry, electron-phonon interactions, quantization, tunneling, and the ballistic to diffusive nature of transport, all combined in a unified approach. This makes it a convenient and accurate way to understand electronic and thermoelectric transport in nanomaterials, beyond semiclassical approximations, and beyond approximations that deal with the complexities of the geometry. We show that the presence of nanoinclusions within a matrix material offers opportunities for only weak energy filtering, significantly lower in comparison to superlattices, and thus only moderate power factor improvements. However, we describe how such nanocomposites can be optimized to limit degradation in the thermoelectric power factor and elaborate on the conditions that achieve the aforementioned mild improvements. Importantly, we show that under certain conditions, the power factor is independent of the density of nanoinclusions, meaning that materials with large nanoinclusion densities which provide very low thermal conductivities can also retain large power factors and result in large ZT figures of merit.

Polyaniline − carbon nanohorn composites as thermoelectric materials

Thermoelectric materials can convert heat into electricity when a temperature gradient is present. The investigation of conductive polymers such as polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) as active materials for thermoelectric generators in the room temperature range is gaining interest because of several key advantages offered by these materials. The relative ease of solution processing, their mechanical stability and flexibility together with low density and low thermal conductivity make conductive polymers suitable for integration in a thermoelectric generator. Polymers offer remarkably low thermal conductivity values but modest Seebeck coefficient and electrical conductivity. In this work, polymer/inorganic nanocomposites of PANI with carbon particles such as single wall carbon nanohorns (SWCNHs) were prepared via solution mixing of the precursors in order to increase the electrical conductivity by means of polymer matrix/nanohorn electronic junctions. The electrical conductivity and Seebeck coefficient were estimated on PANI/SWCNH films and pressed pellets and through-plane thermal conductivity was determined on films. The thermal stability of PANI/SWCNH composites was evaluated by means of TGA/DSC coupled with residual gas analysis. It was found that a proper concentration of SWCNHs in PANI−(+/−)-camphor-10-sulfonic acid (CSA) film was effective in increasing the electrical conductivity without decreasing the Seebeck coefficient. © 2017 Society of Chemical Industry