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11 pages, 1335 KiB

Open AccessArticle

Towards Optimizing Width Modulation for Maximum Thermoelectric Efficiency

by Antonios-Dimitrios Stefanou and Xanthippi Zianni

Micromachines 2023, 14(12), 2176; https://doi.org/10.3390/mi14122176 - 29 Nov 2023

Cited by 1 | Viewed by 604

Abstract

Maximizing thermoelectric efficiency is typically addressed as identical to minimizing parasitic thermal conduction. Such an approach relies on the assumption that the adopted strategy mainly affects phonons, leaving electrons intact, and is not justified in many cases of non-uniform nanostructures such as width-modulated [...] Read more.

Maximizing thermoelectric efficiency is typically addressed as identical to minimizing parasitic thermal conduction. Such an approach relies on the assumption that the adopted strategy mainly affects phonons, leaving electrons intact, and is not justified in many cases of non-uniform nanostructures such as width-modulated nanowaveguides, where both electrons and phonons are significantly affected by width modulation. Here, we address the question of maximizing the thermoelectric efficiency of this class of metamaterials by exploring the effect of the modulation extent on both electron and phonon transport. We investigated the effect of increasing modulation degree on the thermoelectric efficiency, considering the cases of (a) a two-QD modulation and (b) multiple-QD modulations in periodic and aperiodic sequences. We show that the thermoelectric efficiency depends on the coupling between the modulation units and the interplay between periodicity and aperiodicity in the modulation profile. We reveal that the maximization of the thermoelectric power factor is for periodic width-modulation, whereas the maximization of the thermoelectric efficiency is for aperiodic width-modulation profiles that form quasi-localized states for electrons. Our work provides new insight that can be used to optimize width modulation for maximum thermoelectric efficiency. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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10 pages, 5801 KiB

Open AccessArticle

Effect of Composition Adjustment on the Thermoelectric Properties of Mg₃Bi₂-Based Thermoelectric Materials

by Jianbao Yang, Zhibin Wang, Hong Zhao, Xinyu Luo, Wenyuan Han, Hao Wang, Linghao Meng, Xinqi She, Anlong Quan, Yixin Peng, Guoji Cai, Yi Liu, Yong Tang and Bo Feng

Micromachines 2023, 14(10), 1844; https://doi.org/10.3390/mi14101844 - 27 Sep 2023

Viewed by 970

Abstract

Thermoelectric materials are widely used in refrigeration chips, thermal power generation, catalysis and other fields. Mg₃Bi₂-based thermoelectric material is one of the most promising thermoelectric materials. Herein, the Mg₃Bi₂-based samples were prepared by high temperature [...] Read more.

Thermoelectric materials are widely used in refrigeration chips, thermal power generation, catalysis and other fields. Mg₃Bi₂-based thermoelectric material is one of the most promising thermoelectric materials. Herein, the Mg₃Bi₂-based samples were prepared by high temperature synthesis, and the influence of Mg/Sb content on the electrical transport properties and semi-conductivity/semi-metallicity of the materials has been studied. The results indicate that the efficiency of introducing electrons from excess Mg prepared by high temperature synthesis is lower than that introduced by ball milling, due to the high vapor pressure of Mg. The doping of Sb/Te at the Bi site would make it easier for the material to change from p-type conduction to n-type conduction. With the increase in Mg content, the semi-conductivity of the material becomes weaker, the semi-metallicity becomes stronger, and the corresponding conductivity increases. With the increase in Sb content, the samples exhibit the opposite changes. The highest power factor of ~1.98 mWm⁻¹K⁻² is obtained from the Mg_3.55Bi_1.27Sb_0.7Te_0.03 sample. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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11 pages, 8399 KiB

Open AccessArticle

Study on the Targeted Improvement Mechanism of the Carrier Concentration and Mobility of BiCuSeO Ceramics

by Zhibin Wang, Hong Zhao, Xinyu Luo, Wenyuan Han, Hao Wang, Linghao Meng, Xinqi She, Anlong Quan, Yixin Peng, Guoji Cai, Yi Liu, Yong Tang and Bo Feng

Micromachines 2023, 14(9), 1757; https://doi.org/10.3390/mi14091757 - 10 Sep 2023

Cited by 2 | Viewed by 1238

Abstract

BiCuSeO has great application prospects in thermoelectric power generation and thermoelectric catalysis, but it is limited by its lower thermoelectric performance. Herein, BiCuSeO bulk materials were prepared using a solid-phase reaction method and a ball-milling method combined with spark plasma sintering, and then [...] Read more.

BiCuSeO has great application prospects in thermoelectric power generation and thermoelectric catalysis, but it is limited by its lower thermoelectric performance. Herein, BiCuSeO bulk materials were prepared using a solid-phase reaction method and a ball-milling method combined with spark plasma sintering, and then the thermoelectric properties were improved by synergistically increasing carrier concentration and mobility. Al was adopted to dope into the BiCuSeO matrix, aiming to adjust the carrier mobility through energy band adjustment. The results show that Al doping would widen the bandgap and enhance the carrier mobility of BiCuSeO. After Al doping, the thermoelectric properties of the material are improved in the middle- and high-temperature range. Based on Al doping, Pb is adopted as the doping element to dope BiCuSeO to modify the carrier concentration. The results show that Al/Pb dual doping in the BiCuSeO matrix can increase the carrier concentration under the premise of increasing carrier mobility. Therefore, the electrical conductivity of BiCuSeO can be improved while maintaining a large Seebeck coefficient. The power factor of Al/Pb doping reached ~7.67 μWcm⁻¹K⁻² at 873 K. At the same time, the thermal conductivity of all doped samples within the test temperature range maintained a low level (<1.2 Wm⁻¹K⁻¹). Finally, the ZT value of the Al/Pb-doped BiCuSeO reached ~1.14 at 873 K, which is ~2.72 times that of the pure phase, and the thermoelectric properties of the matrix were effectively improved. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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16 pages, 5599 KiB

Open AccessArticle

Numerical and Experimental Analysis of a Prototypical Thermoelectric Generator Dedicated to Wood-Fired Heating Stove

by Krzysztof Sornek and Karolina Papis-Frączek

Micromachines 2023, 14(1), 145; https://doi.org/10.3390/mi14010145 - 5 Jan 2023

Cited by 2 | Viewed by 1499

Abstract

The typical operating range of domestic heating devices includes only heat generation. However, the availability of combined heat and power generation in microscale devices is currently becoming a more and more interesting option. This paper shows the experimental and numerical analysis of the [...] Read more.

The typical operating range of domestic heating devices includes only heat generation. However, the availability of combined heat and power generation in microscale devices is currently becoming a more and more interesting option. This paper shows the experimental and numerical analysis of the possibility of developing a micro-cogeneration system equipped with a wood-fired heating stove and a prototype of the thermoelectric generator equipped with low-price thermoelectric modules. In the first step, mathematical modeling made it possible to analyze different configurations of the hot side of the thermoelectric generator (computational fluid dynamics was used). Next, experiments have been conducted on the prototypical test rig. The maximum power obtained during the discussed combustion process was 15.9 W_e when the flue gas temperature was approximately 623 K. Assuming a case, when such value of generated power occurred during the whole main phase, the energy generated would be at a level of approximately 33.1 Wh_e, while the heat transferred to the water would be approximately 1 078.0 Wh_th. In addition to the technical aspects, the economic premises of the proposed solution were analyzed. As was shown, an installation of TEG to the existing stove is economically not viable: the Simply Payback Time will be approximately 28.9–66.1 years depending on the analyzed scenario. On the other hand, the SPBT would be significantly shorter, when the installation of the stove with an integrated thermoelectric generator was considered (approximately 5.4 years). However, it should be noted that the introduction of the power generating system to a heat source can provide fully or partially network-independent operation of the hot water and heating systems. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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9 pages, 2313 KiB

Open AccessArticle

Thermoelectric Power-Factor of Ag-Doped TiO₂ Thin Film

by Rohaida Usop, Megat Muhammad Ikhsan Megat Hasnan, Mahazani Mohamad, Mohd Khairul Ahmad, Suhana Mohd Said and Faiz Salleh

Micromachines 2022, 13(12), 2169; https://doi.org/10.3390/mi13122169 - 8 Dec 2022

Cited by 1 | Viewed by 1059

Abstract

The thermoelectric power-factor of two types of rutile-phased nanostructured-TiO₂ thin films doped with Ag was investigated at room temperature, by measuring their Seebeck coefficient and electrical conductivity. The thin films, consisting of a nanorod structure (single layer) and nanorod and nanoflower structure [...] Read more.

The thermoelectric power-factor of two types of rutile-phased nanostructured-TiO₂ thin films doped with Ag was investigated at room temperature, by measuring their Seebeck coefficient and electrical conductivity. The thin films, consisting of a nanorod structure (single layer) and nanorod and nanoflower structure (bilayer) of TiO_2, with the addition of different wt.% of AgNO₃ were synthesized on an F:SnO₂-coated glass substrate. The evaluated thermoelectric power-factor was observed to increase with an increasing wt.% of AgNO₃ for both structures, with the bilayer structure increasing three times more than the undoped bilayer-structure, with a value of 148 μWm–¹K^–2 at 0.15 wt.%. This enhancement was due to the increase in electrical conductivity, which compensated for the small changes in the Seebeck coefficient, which were likely due to the increase in carrier concentration. Consequently, an enhancement in the thermoelectric conversion-efficiency of TiO₂ thin film may be observed by Ag doping, without influencing the layer structure and material phase. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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9 pages, 1629 KiB

Open AccessArticle

Phase Formation Behavior and Thermoelectric Transport Properties of S-Doped FeSe_2−xS_x Polycrystalline Alloys

by Okmin Park, Se Woong Lee, Sang Jeong Park and Sang-il Kim

Micromachines 2022, 13(12), 2066; https://doi.org/10.3390/mi13122066 - 25 Nov 2022

Cited by 8 | Viewed by 1383

Abstract

Some transition-metal dichalcogenides have been actively studied recently owing to their potential for use as thermoelectric materials due to their superior electronic transport properties. Iron-based chalcogenides, FeTe₂, FeSe₂ and FeS₂, are narrow bandgap (~1 eV) semiconductors that could [...] Read more.

Some transition-metal dichalcogenides have been actively studied recently owing to their potential for use as thermoelectric materials due to their superior electronic transport properties. Iron-based chalcogenides, FeTe₂, FeSe₂ and FeS₂, are narrow bandgap (~1 eV) semiconductors that could be considered as cost-effective thermoelectric materials. Herein, the thermoelectric and electrical transport properties FeSe₂–FeS₂ system are investigated. A series of polycrystalline samples of the nominal composition of FeSe_2−xS_x (x = 0, 0.2, 0.4, 0.6, and 0.8) samples are synthesized by a conventional solid-state reaction. A single orthorhombic phase of FeSe₂ is successfully synthesized for x = 0, 0.2, and 0.4, while secondary phases (Fe₇S₈ or FeS₂) are identified as well for x = 0.6 and 0.8. The lattice parameters gradually decrease gradually with S content increase to x = 0.6, suggesting that S atoms are successfully substituted at the Se sites in the FeSe₂ orthorhombic crystal structure. The electrical conductivity increases gradually with the S content, whereas the positive Seebeck coefficient decreases gradually with the S content at 300 K. The maximum power factor of 0.55 mW/mK² at 600 K was seen for x = 0.2, which is a 10% increase compared to the pristine FeSe₂ sample. Interestingly, the total thermal conductivity at 300 K of 7.96 W/mK (x = 0) decreases gradually and significantly to 2.58 W/mK for x = 0.6 owing to the point-defect phonon scattering by the partial substitution of S atoms at the Se site. As a result, a maximum thermoelectric figure of merit of 0.079 is obtained for the FeSe_1.8S_0.2 (x = 0.2) sample at 600 K, which is 18% higher than that of the pristine FeSe₂ sample. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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19 pages, 3723 KiB

Open AccessArticle

Computer Simulations of Silicide-Tetrahedrite Thermoelectric Generators

by Rodrigo Coelho, Álvaro Casi, Miguel Araiz, David Astrain, Elsa Branco Lopes, Francisco P. Brito and António P. Gonçalves

Micromachines 2022, 13(11), 1915; https://doi.org/10.3390/mi13111915 - 5 Nov 2022

Cited by 1 | Viewed by 1458

Abstract

With global warming and rising energy demands, it is important now than ever to transit to renewable energy systems. Thermoelectric (TE) devices can present a feasible alternative to generate clean energy from waste heat. However, to become attractive for large-scale applications, such devices [...] Read more.

With global warming and rising energy demands, it is important now than ever to transit to renewable energy systems. Thermoelectric (TE) devices can present a feasible alternative to generate clean energy from waste heat. However, to become attractive for large-scale applications, such devices must be cheap, efficient, and based on ecofriendly materials. In this study, the potential of novel silicide-tetrahedrite modules for energy generation was examined. Computer simulations based on the finite element method (FEM) and implicit finite difference method (IFDM) were performed. The developed computational models were validated against data measured on a customized system working with commercial TE devices. The models were capable of predicting the TEGs’ behavior with low deviations (

\leq

10%). IFDM was used to study the power produced by the silicide-tetrahedrite TEGs for different

Δ T

between the sinks, whereas FEM was used to study the temperature distributions across the testing system in detail. To complement these results, the influence of the electrical and thermal contact resistances was evaluated. High thermal resistances were found to affect the devices

Δ T

up to ~15%, whereas high electrical contact resistances reduced the power output of the silicide-tetrahedrite TEGs by more than ~85%. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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Review

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22 pages, 4196 KiB

Open AccessReview

Recent Progress in Development of Carbon-Nanotube-Based Photo-Thermoelectric Sensors and Their Applications in Ubiquitous Non-Destructive Inspections

by Kou Li, Yuya Kinoshita, Daiki Sakai and Yukio Kawano

Micromachines 2023, 14(1), 61; https://doi.org/10.3390/mi14010061 - 26 Dec 2022

Cited by 12 | Viewed by 3576

Abstract

The photo-thermoelectric (PTE) effect in electronic materials effectively combines photo-absorption-induced local heating and associated thermoelectric conversion for uncooled and broadband photo-detection. In particular, this work comprehensively summarizes the operating mechanism of carbon nanotube (CNT)-film-based PTE sensors and ubiquitous non-destructive inspections realized by exploiting [...] Read more.

The photo-thermoelectric (PTE) effect in electronic materials effectively combines photo-absorption-induced local heating and associated thermoelectric conversion for uncooled and broadband photo-detection. In particular, this work comprehensively summarizes the operating mechanism of carbon nanotube (CNT)-film-based PTE sensors and ubiquitous non-destructive inspections realized by exploiting the material properties of CNT films. Formation of heterogeneous material junctions across the CNT-film-based PTE sensors, namely photo-detection interfaces, triggers the Seebeck effect with photo-absorption-induced local heating. Typical photo-detection interfaces include a channel–electrode boundary and a junction between P-type CNTs and N-type CNTs (PN junctions). While the original CNT film channel exhibits positive Seebeck coefficient values, the material selections of the counterpart freely govern the intensity and polarity of the PTE response signals. Based on these operating mechanisms, CNT film PTE sensors demonstrate a variety of physical and chemical non-destructive inspections. The device aggregates broad multi-spectral optical information regarding the targets and reconstructs their inner composite or layered structures. Arbitrary deformations of the device are attributed to the macroscopic flexibility of the CNT films to further monitor targets from omni-directional viewing angles without blind spots. Detection of blackbody radiation from targets using the device also visualizes their behaviors and associated changes. Full article

(This article belongs to the Special Issue Development of High Performance Thermoelectric Materials towards Applications)

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