Thermoelectric Energy Conversion Research Articles

High performance solid-state thermoelectric energy conversion via inorganic metal halide perovskites under tailored mechanical deformation

High performance solid-state thermoelectric energy conversion via inorganic metal halide perovskites under tailored mechanical deformation

Linear and nonlinear thermoelectric transport in a quantum spin Hall insulators coupled with a nanomagnet

Thermoelectric effects in quantum systems have been focused in recent years. Thermoelectric energy conversion study of systems with edge states, such as quantum Hall insulators and quantum spin Hall insulators, is one of the most important frontier topics in material science and condensed-matter physics. Based on the previous paper (Gresta in Phys Rev Lett 123:186801, 2019), we further investigated the linear and nonlinear thermoelectric transport properties of helical edge states of the quantum spin Hall insulators coupled with double nanomagnet, calculated the Seebeck coefficients S_c and the thermoelectrical figure of merit ZT, discussed the influence of the length of the nanomagnet and the relative tilt angle of component of the magnetization perpendicular on the thermoelectric coefficients (S_c and ZT), and summarized some meaningful conclusions in the linear response regime. In the nonlinear regime, we calculated the equivalent figure of merit ZT_M and the power-generation efficiency eta in different length of the nanomagnet, obtain the temperature difference of achieving optimal thermoelectricity. The results of this paper further confirm that the setup can indeed be used as a device for achieving high performance thermoelectric.

New and Recent Results for Thermoelectric Energy Conversion in Graded Alloys at Nanoscale.

In this article, we review the main features of nonlocal and nonlinear heat transport in nanosystems and analyze some celebrated differential equations which describe this phenomenon. Then, we present a new heat-transport equation arising within the so-called thermomass theory of heat conduction. We illustrate how such a theory can be applied to the analysis of the efficiency of a thermoelectric energy generator constituted by a Silicon–Germanium alloy, as the application and new results for a nanowire of length nm, are presented as well. The thermal conductivity of the nanowire as a function of composition and temperature is determined in light of the experimental data. Additionally, the best-fit curve is obtained. The dependency of the thermoelectric efficiency of the system on both the composition and the difference of temperature applied to its ends is investigated. For the temperatures K, K, and K, we calculate the values of the composition corresponding to the optimal efficiency, as well as the optimal values of the thermal conductivity. Finally, these new results are compared with recent ones obtained for a system of length mm, in order to point out the benefits due to the miniaturization in thermoelectric energy conversion.

Ba1/3CoO2: A Thermoelectric Oxide Showing a Reliable ZT of ∼0.55 at 600 °C in Air.

Thermoelectric energy conversion technology has attracted attention as an energy harvesting technology that converts waste heat into electricity by means of the Seebeck effect. Oxide-based thermoelectric materials that show a high figure of merit are promising because of their good chemical and thermal stability as well as their harmless nature compared to chalcogenide-based state-of-the-art thermoelectric materials. Although several high-ZT thermoelectric oxides (ZT > 1) have been reported thus far, the reliability is low due to a lack of careful observation of their stability at elevated temperatures. Here, we show a reliable high-ZT thermoelectric oxide, Ba1/3CoO2. We fabricated Ba1/3CoO2 epitaxial films by the reactive solid-phase epitaxy method (Na3/4CoO2) followed by ion exchange (Na+ → Ba2+) treatment and performed thermal annealing of the film at high temperatures and structural and electrical measurements. The crystal structure and electrical resistivity of the Ba1/3CoO2 epitaxial films were found to be maintained up to 600 °C. The power factor gradually increased to ∼1.2 mW m–1 K–2 and the thermal conductivity gradually decreased to ∼1.9 W m–1 K–1 with increasing temperature up to 600 °C. Consequently, the ZT reached ∼0.55 at 600 °C in air.

Thermoelectric power generation in the core of a nuclear reactor

Thermoelectric energy converters offer a promising solution to generate electrical power using heat in the nuclear reactor core. Despite significant improvements in thermoelectric efficiency of nanostructured materials, the performance of these advanced materials has yet to be demonstrated in the harsh radiation environment of a reactor core. Herein, we demonstrate a thermoelectric generator (TEG) made from nanostructured bulk half-Heusler (HH) materials generating stable electrical power density > 1140 W/m2 after 30 days in the MIT Nuclear Research Reactor under an unprecedented fast-neutron (>1 MeV) fluence of 1.5 × 1020 n/cm2. Despite an initial degradation due to irradiation damage when operating under relatively low temperatures, our TEG showed a 20-fold increase in power output when operating under high temperature due to in-situ annealing and resulting thermoelectric property recovery. First-principles modeling indicates that a chemically disordered metallic phase was formed under irradiation at lower temperatures, resulting in a drastic degradation in thermoelectric properties, while at sufficiently high temperatures the system returned to the initial chemically ordered HH phase and the thermoelectric properties recovered. Transmission electron microscopy and electron diffraction demonstrated that the chemically disordered phase was formed upon ion irradiation, confirming the prediction from first-principles simulations. The results suggest that with proper control over the TEG operating temperatures, the nanostructured bulk TEGs could produce stable electrical power and operate indefinitely in the core of a nuclear reactor.

Dynamic doping and Cottrell atmosphere optimize the thermoelectric performance of n-type PbTe over a broad temperature interval

High thermoelectric energy conversion efficiency requires a large figure-of-merit, zT, over a broad temperature range. To achieve this, we optimize the carrier concentrations of n-type PbTe from room up to hot-end temperatures by co-doping Bi and Ag. Bi is an efficient n-type dopant in PbTe, often leading to excessive carrier concentration at room temperature. As revealed by density functional theory calculations, the formation of Bi and Ag defect complexes is exploited to optimize the room temperature carrier concentration. At elevated temperatures, we demonstrate the dynamic dissolution of Ag2Te precipitates in PbTe in situ by heating in a scanning transmission electron microscope. The release of n-type Ag interstitials with increasing temperature fulfills the requirement of higher carrier concentrations at the hot end. Moreover, as characterized by atom probe tomography, Ag atoms aggregate along parallel dislocation arrays to form Cottrell atmospheres. This results in enhanced phonon scattering and leads to a low lattice thermal conductivity. As a result of the synergy of dynamic doping and phonon scattering at decorated dislocations, an average zT of 1.0 is achieved in n-type Bi/Ag-codoped PbTe between 400 and 825 K. Introducing dopants with temperature-dependent solubility and strong interaction with dislocation cores enables simultaneous optimization of the average power factor and thermal conductivity, providing a new concept to exploit in the field of thermoelectrics.

Bacterial cellulose-based dual chemical reaction coupled hydrogel thermocells for efficient heat harvesting

Reasonable and efficient utilization of low-grade thermal energy in nature is the choice for sustainable energy development. We demonstrate a bacterial cellulose (BC) hydrogel thermocell (TEC) based on BC electrolyte combined with carbon fiber paper and copper composite electrode sheets. The large specific surface area of carbon fiber paper provides a large number of active sites for thermoelectric ions, which drives the redox reaction inside the electrolyte and stimulates the chemical reaction between the electrolyte and the electrode. The combination of the two chemical reactions significantly improves the thermoelectric performance of the thermocell. The thermopower of the BC-TEC reaches 5.9 mV·K−1 at a temperature difference of 50 K. The TEC consisting of 6-units in series produces an open-circuit voltage of about 2 V and a peak power of 535 μW. The TEC shows new potential and prospects in ambient thermoelectric energy conversion by rationally designing the power generation principle.

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.

Insights into Low Thermal Conductivity in Inorganic Materials for Thermoelectrics.

Efficient manipulation of thermal conductivity and fundamental understanding of the microscopic mechanisms of phonon scattering in crystalline solids are crucial to achieve high thermoelectric performance. Thermoelectric energy conversion directly and reversibly converts between heat and electricity and is a promising renewable technology to generate electricity by recovering waste heat and improve solid-state refrigeration. However, a unique challenge in thermal transport needs to be addressed to achieve high thermoelectric performance: the requirement of crystalline materials with ultralow lattice thermal conductivity (κL). A plethora of strategies have been developed to lower κL in crystalline solids by means of nanostructural modifications, introduction of intrinsic or extrinsic phonon scattering centers with tailored shape and dimension, and manipulation of defects and disorder. Recently, intrinsic local lattice distortion and lattice anharmonicity originating from various mechanisms such as rattling, bonding heterogeneity, and ferroelectric instability have found popularity. In this Perspective, we outline the role of manipulation of chemical bonding and structural chemistry on thermal transport in various high-performance thermoelectric materials. We first briefly outline the fundamental aspects of κL and discuss the current status of the popular phonon scattering mechanisms in brief. Then we discuss emerging new ideas with examples of crystal structure and lattice dynamics in exemplary materials. Finally, we present an outlook for focus areas of experimental and theoretical challenges, possible new directions, and integrations of novel techniques to achieve low κL in order to realize high-performance thermoelectric materials.

Extensive Analysis on the Thermoelectric Properties of Aqueous Zn-Doped Nickel Ferrite Nanofluids for Magnetically Tuned Thermoelectric Applications.

Because of the ever-increasing consumption of energy, higher-efficiency thermoelectric materials are in more demand. In this regard, initially, ZnxNi(1-x)Fe2O4 nanoparticles were synthesized using a co-precipitation technique and investigated using Rietveld refinement and Brunauer-Emmett-Teller (BET) analyses. Then, they were dispersed in water to obtain stable 1 vol % of aqueous ZnxNi(1-x)Fe2O4 nanofluids and their viscous, electrical, thermal, and thermoelectric properties were analyzed in the absence and presence of a magnetic field. The Rietveld refinement revealed the formation of single phase spinel ferrite structures and cationic distribution of ZnxNi(1-x)Fe2O4 nanoparticles, whereas BET analysis revealed the surface area of the nanoparticles. The viscosity studies proved the pseudo-plastic shear thinning behavior and dipole-dipole interactions of ZnxNi(1-x)Fe2O4 nanofluids. The electrical conductivity, thermal conductivity, and Seebeck coefficient studies revealed that the maximum enhancement was observed for the Zn0.2Ni0.8Fe2O4 nanofluid, which was attributed to the enhanced electrical double layer formation and Brownian motion of nanoparticles in the nanofluid. The enhancement in the properties of synthesized nanofluids in the presence of a magnetic field was attributed to the formation of chain-like structures, which was substantiated through the magneto-viscosity studies. The thermoelectric energy conversion efficiency of ZnxNi(1-x)Fe2O4 nanofluids was calculated which showed that the maximum enhancement of 27% was observed in the Zn0.2Ni0.8Fe2O4 nanofluid at 770 G. The observed results proved that the synthesized nanofluids are magnetically tunable thermoelectric materials which are suitable for waste heat energy harvesting applications.

Optimization assisted CFD for using double porous cylinders on the performance improvement of TEG mounted 3D channels

Performance of a thermoelectric generator (TEG) mounted into a channel is analyzed by using double porous cylinders in channel flow with finite element method. COBYLA (Constrained Optimization BY Linear Approximations) algorithm is used to obtain the optimum size and permeability of the porous objects to achieve the highest power. As compared to a non-object channel configuration, the installation of the porous object results in higher power generation. A lower permeability of the double cylinders increases the TEG power while 10.5% increment is obtained when lowest and highest permeability configurations are compared. When sizes of the porous objects are varying up to 19% rise in the TEG power is attained as compared to no-object channel case. The optimum set of parameter to achieve the highest power is obtained as ap1=0.232hz,ap2=0.75hz and Da=10-6. At the optimum conditions, there is 22.5% rise of TEG power when hot side Reynolds number is increased from 200 to 600 while this value is 18% for the no-object case. At the highest nanoparticle loading, 20.5% higher power is obtained at the optimum case when compared to no-object channel case. The optimization assisted computational fluid dynamics (CFD) study of TEG installed channel flow with passive methods is very effective in achieving the best performance as compared to computationally expensive high fidelity multi-parametric CFD. As thermoelectric energy conversion and related devices are used in diverse energy systems technologies including solar-thermal applications, thermal management in different thermal systems, refrigeration and many others, the outcomes and computational methods will be useful for efficient design and optimization studies.

Scanning tunneling microscopy of Bi2Te3 films prepared by pulsed laser deposition: from nanocrystalline structures to van der Waals epitaxy

Bi2Te3 is a material with high efficiency of thermoelectric energy conversion. Recently, it was also recognized as a topological insulator, and is often used as the basis for creation of other types of topological matter. Pulsed laser deposition (PLD) is widely considered as a simple method for growing of multicomponent films, but not as a tool for van der Waals epitaxy. We demonstrate here that the van der Waals epitaxy of Bi2Te3 is indeed impossible in vacuum PLD, but is possible in the presence of a background gas, which is confirmed by the results of scanning tunneling microscopy and spectroscopy studies. Results of ab initio calculations reproduce tunneling spectra of the first three terraces of epitaxial films of Bi2Te3. In addition, an unusual hexagonal superstructure resembling a charge-density wave is observed in overheated films.

Mobility enhancement in heavily doped semiconductors via electron cloaking.

Doping is central for solid-state devices from transistors to thermoelectric energy converters. The interaction between electrons and dopants plays a pivotal role in carrier transport. Conventional theory suggests that the Coulomb field of the ionized dopants limits the charge mobility at high carrier densities, and that either the atomic details of the dopants are unimportant or the mobility can only be further degraded, while experimental results often show that dopant choice affects mobility. In practice, the selection of dopants is still mostly a trial-and-error process. Here we demonstrate, via first-principles simulation and comparison with experiments, that a large short-range perturbation created by selected dopants can in fact counteract the long-range Coulomb field, leading to electron transport that is nearly immune to the presence of dopants. Such “cloaking” of dopants leads to enhanced mobilities at high carrier concentrations close to the intrinsic electron–phonon scattering limit. We show that the ionic radius can be used to guide dopant selection in order to achieve such an electron-cloaking effect. Our finding provides guidance to the selection of dopants for solid-state conductors to achieve high mobility for electronic, photonic, and energy conversion applications.

Electrical mapping of thermoelectric power factor in WO3 thin film

With growing environmental awareness and considerable research investment in energy saving, the concept of energy harvesting has become a central topic in the field of materials science. The thermoelectric energy conversion, which is a classic physical phenomenon, has emerged as an indispensable thermal management technology. In addition to conventional experimental investigations of thermoelectric materials, seeking promising materials or structures using computer-based approaches such as machine learning has been considered to accelerate research in recent years. However, the tremendous experimental efforts required to evaluate materials may hinder us from reaping the benefits of the fast-developing computer technology. In this study, an electrical mapping of the thermoelectric power factor is performed in a wide temperature-carrier density regime. An ionic gating technique is applied to an oxide semiconductor WO3, systematically controlling the carrier density to induce a transition from an insulating to a metallic state. Upon electrically scanning the thermoelectric properties, it is demonstrated that the thermoelectric performance of WO3 is optimized at a highly degenerate metallic state. This approach is convenient and applicable to a variety of materials, thus prompting the development of novel functional materials with desirable thermoelectric properties.

Enhanced Thermoelectric Power Factor in Carrier-Type-Controlled Platinum Diselenide Nanosheets by Molecular Charge-Transfer Doping.

2D transition metal dichalcogenides (TMDCs) have revealed great promise for realizing electronics at the nanoscale. Despite significant interests that have emerged for their thermoelectric applications due to their predicted high thermoelectric figure of merit, suitable doping methods to improve and optimize the thermoelectric power factor of TMDCs have not been studied extensively. In this respect, molecular charge-transfer doping is utilized effectively in TMDC-based nanoelectronic devices due to its facile and controllable nature owing to a diverse range of molecular designs available for modulating the degree of charge transfer. In this study, the power of molecular charge-transfer doping is demonstrated in controlling the carrier-type (n- and p-type) and thermoelectric power factor in platinum diselenide (PtSe2 ) nanosheets. This, combined with the tunability in the band overlap by changing the thickness of the nanosheets, allows a significant increase in the thermoelectric power factor of the n- and p-doped PtSe2 nanosheets to values as high as 160 and 250 µW mK-2 , respectively. The methodology employed in this study provides a simple and effective route for the molecular doping of TMDCs that can be used for the design and development of highly efficient thermoelectric energy conversion systems.

Mechanical, optical, and thermoelectric properties of semiconducting ZnIn2X4 (X=S, Se, Te) monolayers

Mechanical stability of the ZnIn2X4 monolayers. The ZnIn2S4 and ZnIn2Se4 are semiconductors with direct band gaps of 3.94 and 2.77 eV, respectively whereas the ZnIn2Te4 shows an indirect band gap of 1.84 eV at the G0W0 level. The optical properties achieved from the solution of the Bethe-Salpeter equation predict the exciton binding energy of the ZnIn2S4, ZnIn2Se4, and ZnIn2Te4 monolayers to be 0.51, 0.41, and 0.34 eV, respectively, suggesting the high stability of the excitonic states against thermal dissociation. Using the iterative solutions of the Boltzmann transport equation accelerated by machine learning interatomic potentials, the room-temperature lattice thermal conductivity of the ZnIn2S4, ZnIn2Se4, and ZnIn2Te4 monolayers is predicted to be remarkably low as 5.8, 2.0, and 0.4 W/mK, respectively. Due to the low lattice thermal conductivity, high thermopower, and large figure of merit, we propose the ZnIn2Se4 and ZnIn2Te4 monolayers as promising candidates for thermoelectric energy conversion systems. This study provides an extensive vision concerning the intrinsic physical properties of the ZnIn2X4 nanosheets and highlights their characteristics for energy conversion and optoelectronics applications.

Heat and Charge Carrier Flow through Single-Walled Carbon Nanotube Films in Vertical Electrolyte-Gated Transistors: Implications for Thermoelectric Energy Conversion

Heat and Charge Carrier Flow through Single-Walled Carbon Nanotube Films in Vertical Electrolyte-Gated Transistors: Implications for Thermoelectric Energy Conversion

Transport Properties of Novel LaCoTiIn Equiatomic Quaternary Heusler Alloy for Thermoelectric Energy Conversion

The emergence of new thermoelectric materials for energy generation is crucial to satisfying the world's energy demand. The electron charge density and thermoelectric transport properties of the LaCoTiIn quaternary Heusler alloy were investigated in this study. We used the Generalized Gradient Approximation (GGA – PBE) exchange correlation potential to illustrate the physical properties of a material. The electronic structure of the alloy shows half-metallic ferromagnetic behavior. The minority spin channel's small band gap enhances its thermoelectric characteristics. The high electrical conductivity, small thermal conductivity, and good figure of merit all indicate that this material could be a suitable material to employ in thermoelectric energy conversion.

Bacterial cellulose-based hydrogel thermocells for low-grade heat harvesting

• A BC-based hydrogel TEC via a simple impregnation process was prepared. • The feasibility of BC hydrogel as a thermoelectric matrix was confirmed. • TEC generated 0.82 V voltage and 4.5 μW power with 3 pairs of units, at ΔT = 50 K. The hydrogel thermoelectrochemical cells (thermocells, TECs) are a simple, efficient, and inexpensive technology for harvesting low-grade heat from the environment. For the current development, higher mechanical properties and relatively simple and mature production processes are highly desirable and challenging. Herein, readily available bacterial cellulose (BC)-based TECs with Fe(CN) 6 3−/4− redox couple and Fe 2+/3+ redox couple as n, p-type cellulose hydrogel electrolyte via a simple impregnation process are prepared. The Seebeck coefficient can reach 4.5 mV∙K −1 for n-type TEC and 0.72 mV∙K −1 for p-type TEC. The proof-of-concept thermoelectric device, connecting in series with 3 pairs of units, can generate 0.82 V voltage and 4.5 μW peak power. The bacterial cellulose matrix is commercially available and can be produced in a large area, demonstrating the hope of being an energy carrier of thermoelectric ions for thermoelectric energy conversion. The bacterial cellulose-based TECs have potential applications in wearable electronic devices, energy storage devices, temperature sensing devices and so on.

Controlling the electrical resistivity of porous silicon carbide ceramics and their applications: A review

AbstractPorous silicon carbide (SiC)‐based ceramics are widely used in numerous applications of technical importance owing to their exceptional structural (e.g., excellent chemical, mechanical, and thermal stability) and functional (e.g., controlled electrical resistivity) properties. Porous SiC with controlled electrical resistivity is required for various advanced applications, for example, power electronic devices, semiconductor processing parts, fusion reactors, thermoelectric energy conversion, electromagnetic shielding, and environmental applications such as heatable filters. The electrical properties of sintered porous SiC are significantly affected by its chemical composition, processing conditions, and microstructure. This article reviews the influence of certain critical factors, such as the polytype, doping conditions, porosity (%), additive composition (oxide additives, element additives, metal nitride/carbide additives, etc.), and processing conditions on the electrical resistivity of porous SiC. Novel applications of porous SiC with controlled electrical resistivity are also discussed in this review.