Thermoelectric Efficiency Research Articles

High Dimensionless Figure of Merit and Efficiency Thermoelectrics for Operation below Sub-250 °C─Origin of Colossal Seebeck Coefficient with Phonon Assisting, Coexistence with Electrical Conductivity, and Device Application for Their Multilayered Structure.

Thermoelectric (TE) devices recycle high-temperature waste-heat efficiently, but waste-heat below sub-250 °C remains uncaptured. As promoting full autonomy for the Internet of Things (IoT), we present a TE generator using multilayered pseudo-p-type GaN/TiN/GaN and n-type TiO2/TiN/TiO2 TE one-leg devices, where heterozygous of outer/inner layers demonstrates the functions of a colossal Seebeck coefficient (S = +15,000 μV K-1) with phonon-assist hopping, controlling by the porosity for reducing thermal conductivity (κ), a high electric conductivity (σ) with reducing κ by outer layers, and σ-S coexistence over singular curve by the asymmetric electrode configuration. S is elucidated hopping among inner grains and the space charge (SC) grain boundary (GB) of 100 μm regions within Debye length. By assisting phonon, SC capturing, hopping-up (recoiling, pseudo-p-type) or -down (n-type) over potential barriers at GBs are investigated. The devices showed high ZT (∼2.2), low κ (15.2 W m-1 K-1), and outputs at sub-250 °C, which is promising for waste heat recycling (predicted efficiency: 12.5%).

The Design of Intrinsically Conductive Metal‐Organic Frameworks for Thermoelectric Materials

Thermoelectric (TE) materials offer exciting promise in the development of sustainable, green energy alternatives. Ideal TE materials promote high electrical conductivity, whilst effectively scattering phonons for reduced thermal conductivity, thus giving the phonon‐glass electron‐crystal concept. Metal‐organic frameworks (MOFs) have emerged as a versatile class of materials that could meet these criteria. The high crystallinity of MOFs can offer effective pathways for charge transport whilst their intrinsic high porosity yields ultralow thermal conductivity. The high structural diversity of MOFs, owing to the versatile coordination of metal cation/cluster and linker offers the potential to systematically tune their properties for TE performance. This review examines the advancement in the design strategies that have thus far been implemented toward intrinsically conductive MOFs and how these should be tailored for application toward TE materials. By addressing the challenges and leveraging the unique properties of MOFs, future research can pave the way for innovative and efficient TE MOF materials.

Quadruple-band synglisis enables high thermoelectric efficiency in earth-abundant tin sulfide crystals.

Thermoelectrics have been limited by the scarcity of their constituent elements, especially telluride. The earth-abundant, wide-bandgap (Eg ≈ 46 kBT) tin sulfide (SnS) has shown promising performance in its crystal form. We improved the thermoelectric efficiency in SnS crystals by promoting the convergence of energy and momentum of four valance bands, termed quadruple-band synglisis. We introduced more Sn vacancies to activate quadruple-band synglisis and facilitate carrier transport by inducing SnS2 in selenium (Se)-alloyed SnS, leading to a high dimensionless figure of merit (ZT) of ~1.0 at 300 kelvin and an average ZT of ~1.3 at 300 to 773 kelvin in p-type SnS crystals. We further obtained an experimental efficiency of ~6.5%, and our fabricated cooler demonstrated a maximum cooling temperature difference of ~48.4 kelvin at 353 kelvin. Our observations should draw interest to earth-abundant SnS crystals for applications of waste-heat recovery and thermoelectric cooling.

Cu‐In Co‐Doping and Layered Directional Sintering for High Thermoelectric Efficiency and Mechanical Strength in Bi2(Te,Se)3

Cu‐In Co‐Doping and Layered Directional Sintering for High Thermoelectric Efficiency and Mechanical Strength in Bi₂(Te,Se)₃

Optical Phonon Decay and Improved Thermoelectric Efficiency in p-Type Mg3Sb2.

The Mg3Sb2-based layered compounds exhibit exceptional thermoelectric properties over a wide temperature range and possess the potential to supplant traditional Bi2Te3 modules with reliable and economical Mg3Sb2-based thermoelectric devices, contingent upon the availability of a complementary p-type Mg3Sb2 material with high thermoelectric efficiency comparable to that of n-type Mg3Sb2. We provide a simpler method involving the codoping of monovalent atoms (K and Na) at the Mg site of the Mg3Sb2 lattice to improve the thermoelectric performance of p-type Mg3Sb2. K-Na codoping results in a peak power factor of around 0.85 mW/mK2 at 675 K in Mg2.97K0.02Na0.01Sb2 by enhancing the carrier concentration at the Fermi level. Furthermore, the temperature-dependent development of the Raman modes substantiates the existence of significant lattice anharmonicity in Mg2.97K0.02Na0.01Sb2, ascribed to volumetric quasi-anharmonicity and three- and four-phonon interactions. As a result, decay of optical phonon happens at higher temperatures, yielding an exceptionally low lattice thermal conductivity of 0.38 W/mK at 675 K in Mg2.97K0.02Na0.01Sb2, the lowest recorded in p-type Mg3Sb2 materials. The thermoelectric figure of merit for Mg2.97K0.02Na0.01Sb2 attains 0.9 at 675 K, representing the highest documented value for double-doped p-type Mg3Sb2 materials thus far. Our extensive findings validate the optical phonon decay and improvement in thermoelectric efficiency of p-type Mg3Sb2 via codoping with monovalent atoms for midtemperature thermoelectric applications.

Achieving Superior Thermoelectric Performance in Methoxy-Functionalized MXenes: The Role of Organic Functionalization.

Thermoelectric technology enables the direct and reversible conversion of heat into electrical energy without air pollution. Herein, the stability, electronic structure, and thermoelectric properties of methoxy-functionalized M2C(OMe)2 (M = Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, and W) were systematically investigated using first-principles calculations and semiclassical Boltzmann transport theory. All MXenes, except those with M = Cr, Mo, and W, can be synthesized by substituting Cl- and Br-functionalized MXenes with deprotonated methanol, with stability governed by the M-O bond strength. Notably, semiconductors Sc2C(OMe)2 and Y2C(OMe)2 exhibit exceptionally high peak ZT values of 15.02 and 12.11 under n-type doping at 900 K, achieving a remarkable thermoelectric conversion efficiency of 53% at a temperature difference of 600 K, outperforming current high-performance thermoelectric materials. This superior performance is attributed to the weak electron-withdrawing nature of the methoxy group, which enhances nonbonding d electrons, combined with flat and degenerate band edges, and strong coupling between acoustic and optical phonons. Together, these features sustain a high Seebeck coefficient, improve electrical conductivity, and suppress lattice thermal conductivity. These findings present an effective organic functionalization strategy for designing high-performance MXenes for industrial applications and offer valuable insights for developing next-generation thermoelectric materials.

High density lath twins lead to high thermoelectric conversion efficiency in Bi2Te3 modules.

Thermoelectric (TE) generators based on bismuth telluride (Bi2Te3) are recognized as a credible solution for low-grade heat harvesting. In this study, an combinative doping strategy of both the donor (Ag) and the acceptor (Ga) in Ag9GaTe6 as dopants is developed to modulate the microstructure and improve the ZT value of p-type Bi0.4Sb1.6Te3. Specifically, the distribution of Ag and Ga in the matrix synergistically introduces multiple phonon scattering centers including lath twins, triple junction boundaries, and Sb-rich nanoprecipitates, leading to an obviously suppressed lattice thermal conductivity of 0.50 W m-1 K-1 at 300 K. At the same time, such unique microstructures of lath twins synergistically enhance the room-temperature power factor to 48.8 μW cm-1 K-2 and improve the Vickers hardness to 0.90 GPa. Consequently, a high ZT of 1.40 at 350 K and ZTave of 1.24 (300-500 K) are achieved in the Bi0.4Sb1.6Te3 + 0.03 wt% Ag9GaTe6 sample. Based on that, a competitive conversion efficiency of 6.5% at ΔT = 200 K is obtained in the constructed 17-couple TE module, which exhibits no significant change in the output property after 30 thermal cycle tests benefiting from the stable microstructure.

Effect of hot isostatic pressing treatment on the thermoelectric power factors of zinc oxides

The effect of hot isostatic pressing (HIP) on the thermoelectric power factor of zinc oxide (ZnO) has been examined. ZnO is expected to be a potential n-type oxide thermoelectric material that could enhance the thermoelectric conversion efficiency. The HIP treatment is useful for densifying the material and controlling crystal defects in the material by applying high temperatures and pressures simultaneously. Furthermore, the atmosphere during HIP treatment can be controlled to enable the application of this technique to both metallic and oxide materials. The thermoelectric power factor of ZnO increased due to a notable increase in electrical conductivity, although the Seebeck coefficient decreased by approximately 50% following HIP treatment under argon gas. The increase in the thermoelectric power factor is attributed to the oxygen vacancies introduced into ZnO subsequent to the HIP treatment. Consequently, HIP treatment represents a promising approach for enhancing the thermoelectric power factor of ZnO.

Improving Efficiency of AB-Class Audio Power Amplifier Using Thermoelectric Generators

Since circuit-based solutions for increasing the efficiency of Class AB audio amplifiers have reached their peak, this article presents a non-circuit-based approach for the same purpose. The output transistors of this class of amplifiers dissipate a significant amount of thermal energy, resulting in relatively low amplifier efficiency and requiring the transistors to be mounted on large heatsinks. This study was conducted with the aim of capturing the waste heat energy dissipated by the output transistors and converting it into electrical energy using thermoelectric generators (TEGs), which can then be used to increase the efficiency of the amplifier system. In addition to improving efficiency, this study aims to determine the extent to which heatsinks with smaller dimensions can be used in combination with the amplifier through the use of TEGs, potentially leading to a wider commercial application of Class AB audio amplifiers. The experimental results show that the thermoelectric conversion efficiency of TEGs reached 1.097% in the best case, indicating a potential increase of 0.275% in the overall efficiency of the amplifier system. These results show that the low thermoelectric efficiency of TEGs is a limiting factor that prevents a breakthrough in improving the efficiency of the power amplifier system with the proposed non-circuit-based approach.

DFT-based computational investigation of the structural, electronic, and thermoelectric properties oftransition-metal hydride VH2.

Vanadium hydride is of significant interest because of its potential applications in thermoelectric materials and hydrogen storage technologies. Understanding its structural, electronic, and thermoelectric properties is crucial for optimizing its performance in these applications. This study investigates these properties via density functional theory (DFT), revealing key insights into its stability and efficiency as a thermoelectric material. In this work, the structural, electronic, and thermoelectric properties of cubic VH2 were investigated using the GGA approach within the framework of DFT. The band structure and density of states demonstrate the metallic nature of these compounds. Using the semi-empirical Boltzmann's approach implemented in the BoltzTraP code, transport parameters, such as the Seebeck coefficient, electrical conductivity, thermal conductivity, and figure of merit as a function of the chemical potential, are computed at a temperature gradient of 500K. For the VH2 compound, the thermal and electrical conductivities and Seebeck coefficient are greater for p-type doping and n-type doping. The moderate values of the figure of merit obtained for these materials indicate that these materials have applicability where small values of thermoelectric efficiency are required, and higher values can harm the process. The maximum values of the Seebeck coefficient for VH2 against chemical potential values ranging between 0.095 and - 0.095eV in the p-type region and n-type region are 2.28µV/K and - 2.27µV/K, respectively. The highest value of electrical conductivity per relaxation time in the chemical potential range between - 0.07 and 0.07eV in the p-type region is 5.3 × 10201/Ωms, and that in the n-type region is 1.97 × 10201/Ωms. The maximum dimensionless figure of merit value for VH2 is 0.020.

Realizing a High Thermoelectric Conversion Efficiency in Zintl‐phase NaCdSb via Suppressing the Intrinsic Carrier Excitation

AbstractZintl‐phase NaCdSb compound exhibits exceptional intrinsic thermoelectric performance. However, the low‐temperature carrier concentration of NaCdSb significantly deviates from the ideal, which greatly limits its thermoelectric efficiency. Herein, a stepwise strategy is proposed to enhance the thermoelectric performance of the NaCdSb‐based Zintl phase. This approach effectively improves the power factor while maintaining low lattice thermal conductivity. Consequently, the Na0.99Cd0.995Ag0.005Sb achieves a zT value of 1.41 at 673 K, with an average zT of 0.81 over the temperature range of 300–673 K. Furthermore, the NaCdSb‐based single‐leg device demonstrates a respectable conversion efficiency of ≈7% at a temperature difference of 373 K. These findings highlight the potential of 1‐1‐1 type Zintl‐phase NaCdSb as a high‐performance thermoelectric material. This breakthrough encourages further research into Zintl‐phase thermoelectric materials.

Enhancing room temperature thermoelectric efficiency in zigzag phosphorene nanoribbon junctions through Quasi-Flat impurity bands

Abstract In this study, a novel approach has been utilized to Please specify the corresponding author.explore the room temperature thermoelectric properties of zigzag phosphorene nanoribbon-based monolayer-bilayer-monolayer junctions. To achieve thermoelectric properties at room temperature, a quasi-flat energy band with limited width is required. It has been demonstrated, for the first time, that such bands can be observed by considering a junction of the monolayer and bilayer phosphorene nanoribbons. By adjusting the ribbon widths, quasi-flat bands are produced. This geometrical problem is solved using analytical calculations for a general system and applied to phosphorene. We show that the edge states of phosphorene resemble a one-dimensional tight-binding system, with a close agreement between their results. Using the introduced approach, we calculate the electronic energy band structure of the specified system. Initially, we demonstrate that the formation of zigzag monolayer-bilayer-monolayer junctions can lead to the emergence of quasi-flat impurity bands within the energy bandgap. Furthermore, we show that utilizing these structures at room temperature, across a wide range of lead temperature differences, results in significant output electrical power and improved thermoelectric efficiency. The electrical power and thermoelectric efficiency are examined as functions of applied bias voltage and average chemical potential. Additionally, we explore how the output electrical power, thermoelectric efficiency, and efficiency at maximum power vary with the temperature difference between the leads at the ends of the structure.

On the structural, electronic, and thermoelectric properties of EuMg2X2 (X = P, As, Sb, Bi) zintl phase; A first principles investigations

Abstract The key solution to the now-a-days energy crisis is the conversion of waste heat into useful electrical energy. In this work, the structural, electronic, and thermoelectric characteristics of EuMg2X2 (X = P, As, Sb, Bi) zintl materials have been investigated comprehensively through first principles studies. Structural analysis shows that our measured values fit well with the previous available experimental data. Three potential functionals, PBE GGA, TB-mBJ, and hybrid functional (YS-PBE0), have been used to study the electronic behavior of the titled compounds. EuMg2X2 (X = P, As, Sb, Bi) reveal band gaps of 0.83 eV, 0.72 eV, 0.34 eV, and 0.41 eV, respectively, through hybrid functional (YS-PBE0). Density of states (DOS) and partial density of states (PDOS) studies reveals the role offered by different atomic orbitals in the formation of electronic band structures of the samples. Similarly, thermoelectric tone of the said compounds is calculated by virtue of BoltzTraP2 computational code. The ultralow thermal conductivity and optimum level of carriers’ concentration encompass these materials to be good thermoelectrics with better and reasonable thermoelectric efficiency (ZTe).

Electronic Nature and Thermoelectric Characteristics of Cubic LaPb3 LaIn3 and LaTl3 Compounds: B3PW91 Approach

In this paper the structural, electronic and transport properties of the strongly correlated intermetallics LaX3 (X=Pb, In and Tl) in the space group Pm-3m (221) have been investigated using B3PW91 hybrid functional within the framework of density functional theory. These compounds have 4f orbitals and hence strong electron-electron correlation effect is expected, therefore, the electronic properties are also calculated with the B3PW91 hybrid functional and the effect of B3PW91 hybrid functional on the density of states is discussed in details. The band structure and density of states, demonstrate the metallic nature of these compounds. Using the semi-empirical Boltzmann’s approach implemented in the BoltzTraP code, the transport parameters, such as the Seebeck coefficient, electrical conductivity, thermal conductivity and figure of merit as a function of the chemical potential are computed at a temperature gradient of 500 K. For all materials the thermal and electrical conductivities, and Seebeck coefficient has higher values for n-type doping in comparison with p-type doping. The moderate values of figure of merit obtained for these materials indicate that these materials have applicability where small values of thermoelectric efficiency are required and higher values can harm the process but need experimental verification. LaIn3 has the highest value of electrical conductivity per relaxation time and thermal conductivity per relaxation time are 9.43 x 1020 1/Ωms and 107.65 x 1014 W/mKs respectively. LaTl3 has the highest figure of merit among these materials.

Enhancing thermoelectric efficiency of highly conductive CuSbTe2 alloy by reducing electrical thermal conductivity via heavy Se doping.

Recently, CuSbTe2, one of the I-V-VI-based compounds, has received attention as a promising thermoelectric (TE) material that exhibits a narrow bandgap with high electrical conductivity. In this study, the evolution of electrical and thermal transport properties of CuSbTe2 by heavy Se doping was investigated by synthesizing a series of CuSb(Te1-xSex)2 (x = 0, 0.1, 0.2, 0.3, and 0.4) compositions. The high electrical conductivity of CuSbTe2 (5400 S/cm) is gradually decreased to 1800 S/cm by Se doping with x = 0.4 at 300K with decreased carrier concentration and mobility. Due to this large reduction in electrical conductivity, the power factor of pristine CuSbTe2 significantly decreased to 0.98 mW/mK2 for x = 0.4 by 25%, along with reduced density-of-states effective mass at 550K. Nevertheless, the lattice thermal conductivity was reduced by 5%, and the electrical thermal conductivity was significantly reduced by 67% for x = 0.4 at 550K. Consequently, the total thermal conductivity of pristine CuSbTe2 (2.76 W/mK) is significantly reduced to 1.65 W/mK for x = 0.4 by 40%, mainly owing to the significant reduction of electrical thermal conductivity, which originates from the reduced electrical conductivity. Therefore, an enhanced TE figure of merit (zT) of 0.33 at 550K is observed for CuSb(Te0.6Se0.4)2 (x = 0.4), which was 26% higher than that of CuSbTe2. In addition, the expected zT for various carrier concentrations is calculated by using a single parabolic band model. It was found that the zT could be further enhanced by reducing the carrier concentration, which can be achieved by further doping of electrons.

First principles study of thermoelectric performance and efficiency of the ternary half-Heusler semiconductor LiMgAs: using GGA and meta-GGA methods

First principles study of thermoelectric performance and efficiency of the ternary half-Heusler semiconductor LiMgAs: using GGA and meta-GGA methods

A novel flow channel inspired by classical mathematical function: Enhancing output performance and low-grade heat recovery efficiency of thermal regeneration ammonia-based flow battery

Thermal Regeneration Ammonia-based Flow Battery (TRAFB) faces significant challenges in enhancing its output performance and low-grade waste heat recovery efficiency due to limitations in mass transfer and an incomplete understanding of the mass transfer mechanism. To address these issues, this study innovatively introduces a novel sinusoidal wave flow channel (SWFC), which is inspired by the classic mathematical function. The impact of the SWFC on TRAFB performance is thoroughly discussed and compared in detail with the conventional straight flow channel (SFC). Most importantly, this work unveils for the first time the distribution mechanism of the three mass transfer modes in TRAFB, which are convection, diffusion, and electrophoretic mass transfer. The main findings reveal that the mass transfer performance of TRAFB is primarily governed by convection and diffusion, with electrophoretic mass transfer playing a minimal role, and there is a threshold of current density beyond which the dominant mass transfer mechanism transitions from convection to diffusion. The unique design of the SWFC, which induces the Venturi effect, significantly enhances the overall mass transfer performance of the TRAFB due to the distinct local acceleration, achieving a remarkable enhancement in flux of up to 118.48 times. By optimizing the amplitude and period, the battery's output performance can be further enhanced, with the maximum peak power achieved by the SWFC with an amplitude of 0.8 mm and a period of 0.5π, which is 95.63 % over the SFC. Notably, the SWFC also excels in improving the thermoelectric conversion efficiency, particularly at high current densities, achieving an enhancement of up to 9.81 times.

Solvent-assisted thermogalvanic cell for enhanced low-grade heat harvesting over an extended temperature range

In the pursuit of sustainable energy harvesting from low-grade heat, thermogalvanic cells (TGCs) have received considerable attention, but still confront profound challenges in efficiency and cost-effectiveness, limiting their real-world applications. To expedite the deployment of TGCs, this study delves into the mechanistic interplay of three crucial determinants: intrinsic temperature coefficient, concentration gradient, and activity coefficient of redox couples, elucidating their impact on TGCs' thermoelectric performance. We report a solvent-assisted liquid-state thermogalvanic cell (SA-LTC) by incorporating organic solvents into the sodium ferrocyanide-based TGCs system. With ethanol as a regulator to the concentration gradient and solvation structure, the temperature coefficient of [Fe(CN)6]3-/4- can be enhanced from − 1.39 to − 4.32 mV K−1, leading to a five-fold increase in thermoelectric power and efficiency. Meanwhile, ethanol imparts a lower freezing point and wider working temperature range to the system, showing its better environmental adaptability. In particular, SA-LTC performs better at lower temperatures, at which it achieved a record-high temperature coefficient of − 5.26 mV K−1 and a power density of 2.17 mW m−2 K−2 at 10–20 °C. This study not only provides useful guidance to the optimization of electrolyte design, but also highlights the potential of TGCs for sustainable energy conversion in varied thermal conditions for practical applications.

Theoretical insights into Sb2Te3/Te van der Waals heterostructures for achieving very high figure of merit and conversion efficiency

Thermoelectric technology offers a promising solution for sustainable energy conversion, but maximizing efficiency and figure of merit (ZT) remains a significant challenge. This work explores the novel structural, electronic, and thermoelectric properties of Sb2Te3/Te van der Waals heterostructures (vdWHs) through first-principles computation and Boltzmann transport theory. Our study reveals that the Sb2Te3/Te vdWHs exhibit very low lattice thermal conductivity (0.28 Wm−1K−1) and high Seebeck coefficient (811 μVK−1), driven by energy-filtering effects across the interface and a band gap of 0.47 eV. Notably, the calculated ZT reaches a record-high value of 8.83 at 400 K, substantially surpassing previous benchmarks for similar materials. Unlike prior studies, we extend our investigation by tuning the dimensions to 2 × 2 × 1 and 3 × 3 × 1 supercells and exploring tri-layer Te/Sb2Te3/Te vdWHs. Our results show that the ZT of the 2 × 2 × 1 supercell reaches an even higher value of 9.14, further exceeding the performance of the unit cell. Additionally, the heterostructures demonstrate a remarkable thermoelectric conversion efficiency (η) of 32.25 % and thermionic refrigeration efficiency surpassing 51.9 % of Carnot efficiency at 400 K, highlighting their potential for high-performance cooling applications. These findings significantly advance the integration of high-efficiency heat-to-electricity conversion and cooling within a single material system, setting a new benchmark for thermoelectric performance and establishing Sb₂Te₃/Te vdWHs as a leading candidate for next-generation thermoelectric and electronic technologies.

Molecular Engineering for Future Thermoelectric Materials: The Role of Electrode and Metal Components in Molecular Junctions.

As global temperatures increase due to climate change, the accumulation of excess heat on Earth presents a valuable resource that can be harnessed for electricity generation using thermoelectric materials. However, the intricate structures of bulk thermoelectric materials pose significant challenges to their comprehensive understanding and limit performance. Additionally, their relatively high production costs present practical obstacles. A promising solution to these issues lies in molecular control and the use of molecular junctions. Molecules are predicted to surpass the performance of existing bulk materials in energy conversion because they can be chemically tuned to achieve high thermoelectric efficiencies. This review identifies the thermoelectric parameters that affect the performance of molecular junctions. It also explores various experimental platforms for measuring thermoelectric performance from single molecules to assemblies of hundreds of molecules. Finally, it highlights recent advancements in thermoelectric molecular junctions, focusing on the crucial roles of electrodes and metal components within the molecules, such as Ru complexes, metalloporphyrins, metallocenes, conjugated silane wires, and endohedral metallofullerenes. Ultimately, our review provides a comprehensive analysis of strategies to enhance the thermoelectric efficiency of molecular junctions.