Excellent Thermoelectric Performance Research Articles

Highly enhanced stability and thermoelectric performance of copper sulfides-based composites by multiphase engineering

Interfaces play a key role in affecting carrier, ion and phonon migration, and constructing appropriate phase interfaces allows for synergistically improving the related physical performance. Herein, the effects of various interfaces on electronic and thermal transport in copper sulfide are studied. Dramatically improved mechanical properties and service stability in copper sulfide-based composites are realized while excellent thermoelectric performance is maintained by employing multiphase engineering. The phase composition and intrinsically excessive hole concentration of copper sulfide have been elaborately tailored by regulating Cu vacancies after compositing insulated boron, leading to a significantly optimized Seebeck coefficient. The enhanced phonon scattering effect by high-density interfaces and the deteriorated electrical conductivity contribution result in the overall reduced thermal conductivity. A peak ZT of 1.32 at 773 K could be achieved in the Cu1.8S-0.75 wt% B bulk specimen. In addition, multiscale boron inclusions favor improving mechanical strength by dispersing strengthening. More importantly, spontaneously generated nanoprecipitates inhibit further sulfur volatilization in the matrix, and the introduced interfaces are beneficial for suppressing Cu ion long-range migration as well, which improves the service stability of copper sulfide-based bulk composites. Broadly, the strategy of constructing multiphase by compositing insulated particles paves an important way toward reasonable design of excellent TE materials.

Deep Dive into Lattice Dynamics and Phonon Anharmonicity for Intrinsically Low Thermal Expansion Coefficient in CuS

AbstractScientists enquire about materials engineered with high nanoparticle densities with reduced thermal conductivity and excellent thermoelectric performance. An emerging mineral, copper sulfide (CuS) promises a novel paradigm in the proximity of pressure‐driven structural phase transitions to tune its functional and mechanical properties. Though CuS is a thermoelectric material with low lattice thermal conductivity ( ), improvement of its remains a challenge to be addressed. Moreover, the underlying mechanism governing pressure‐induced phase transformation and reasons for intrinsically small remains completely unexplored. In this study, by combining in‐situ vibrational spectroscopy and ab initio calculations, we reveal that strong phonon anharmonicity under high pressure and low temperature demonstrates a promising approach to decreasing efficiently and boosts thermoelectric figure of merit by 2.7 times from its ambient value. A large mode Grüneisen parameter and short lifetimes for acoustic phonons contribute significantly to its thermal transport.

Thermal transport and thermoelectric properties of alkali-metal telluride Na2Te from first-principles study

The excellent thermoelectric performance of alkali-metal telluride Na2Te has been systematically studied from the electronic and phonon transport properties within the density functional theory combined with the Boltzmann transport theory framework. The phonon dispersion without any imaginary mode demonstrates that the Na2Te compound is dynamically stable. The calculated lattice thermal conductivity is as small as 3.01 W m−1 K−1 at room temperature, suggesting that Na2Te can serve as a promising thermoelectric material. The related anharmonic effect parameters, phonon lifetime and Grüneisen parameter, are discussed to further explain the lattice thermal conductivity. Also, the electronic transport parameters, such as Seebeck coefficient S, electrical conductivity σ, and electronic thermal conductivity κe, are investigated to determine the thermoelectric performance by utilizing the semi-classical Boltzmann transport theory. The final figure of merit ZT can be evaluated based on the lattice thermal conductivity and the corresponding electronic transport coefficients. The maximum ZT of 1.53 can be achieved at a carrier concentration n = 3.08 × 1020 cm−3 for p-type Na2Te at T = 900 K, greatly larger than that of the n-type Na2Te (0.86), suggesting that the Na2Te can be a potential p-type thermoelectric material.

High figure-of-merit and power generation in high-entropy GeTe-based thermoelectrics

The high-entropy concept provides extended, optimized space of a composition, resulting in unusual transport phenomena and excellent thermoelectric performance. By tuning electron and phonon localization, we enhanced the figure-of-merit value to 2.7 at 750 kelvin in germanium telluride-based high-entropy materials and realized a high experimental conversion efficiency of 13.3% at a temperature difference of 506 kelvin with the fabricated segmented module. By increasing the entropy, the increased crystal symmetry delocalized the distribution of electrons in the distorted rhombohedral structure, resulting in band convergence and improved electrical properties. By contrast, the localized phonons from the entropy-induced disorder dampened the propagation of transverse phonons, which was the origin of the increased anharmonicity and largely depressed lattice thermal conductivity. We provide a paradigm for tuning electron and phonon localization by entropy manipulation, but we have also demonstrated a route for improving the performance of high-entropy thermoelectric materials.

Toward Precision Recognition of Complex Hand Motions: Wearable Thermoelectrics by Synergistic 2D Nanostructure Confinement and Controlled Reduction

AbstractSmart wearable electronics have attracted increasing attention because of their great prospects in motion monitoring. To date, a specific design of thermoelectric wearable devices aiming at precision monitoring is still challenging, although thermoelectric materials and devices have witnessed significant developments. In this work, intercalated composites of reduced graphene oxide/reduced poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (rGO/rPEDOT:PSS) are reported through the insertion of PEDOT:PSS into 2D graphene oxide layers followed by precise optimization of oxidation‐level of composite, exhibiting an outstanding thermoelectric performance along with excellent thermoelectric stability and mechanical flexibility. Furthermore, a novel‐concept, simple‐structural, self‐powered thermoelectric wearable sensor is demonstrated with rGO/rPEDOT:PSS composite as the active sensing component of the thermoelectric device. Combined with the excellent thermoelectric performance, ingenious device design, and optimized algorithm, the thermoelectric wearable device achieves precision recognition of various hand motions. This study provides a new way to design wearable sensors toward the precision recognition of human motions.

Thermodynamic Characterization of a Highly Transparent Microfluidic Chip with Multiple On-Chip Temperature Control Units

Indium tin oxide (ITO) is a functional material with great transparency, machinability, electrical conductivity and thermo–sensitivity. Based on its excellent thermoelectric performance, we designed and fabricated a multilayer transparent microfluidic chip with multiple sets of on–chip heating, local temperature measurement and positive on–chip cooling function units. Temperature control plays a significant role in microfluidic approaches, especially in the devices that are designed for bioengineering, chemical synthesis and disease detection. The transparency of the chip contributes to achieve the real–time observation of fluid flow and optical detection. The chip consists of a temperature control layer made with an etched ITO deposited glass, a PDMS (polydimethylsiloxane) fluid layer, a PDMS cooling and flow control layer. The performances of the ITO on–chip microheaters, ITO on–chip temperature sensors and two coolants were tested and analyzed in different working conditions. The positive on–chip heating and cooling were proved to be area-specific under a large temperature–regulating range. This PDMS–ITO–glass based chip could be applied to both temporal and spatial stable temperature–regulating principles for various purposes.

Novel closed-cycle reaction mode for totally green production of Cu1.8Se nanoparticles based on laser-generated Se colloidal solution

Non-stoichiometric copper selenide (Cu2 – x Se, x = 0.18 ∼ 0.25) nanomaterials have attracted extensive attentions due to their excellent thermoelectric, optoelectronic and photocatalytic performances. However, efficient production of Cu2 – x Se nanoparticles (NPs) through a green and convenient way is still hindered by the inevitable non-environmentally friendly operations in common chemical synthesis. Herein, we initially reveal the coexistence of seleninic acid content and elemental selenium (Se) NPs in pulsed laser-generated Se colloidal solution. Consequently, we put forward firstly a closed-cycle reaction mode for totally green production of Cu1.8Se NPs to exclude traditional requirements of high temperature and toxic precursors by using Se colloidal solution. In such closed-cycle reaction, seleninic acid works as the initiator to oxidize copper sheet to release cuprous ions which can catalyze the disproportion of Se NPs to form and Se2– ions and further produce Cu2 – x Se NPs, and the by-product ions promote subsequent formation of cuprous from the excessive Cu sheet. In experiments, the adequate copper (Cu) sheet was simply dipped into such Se colloidal solution at 70 °C, and then the stream of Cu1.8Se NPs could be produced until the exhaustion of selenium source. The conversion rate of Se element reaches to more than 75% when the size of Se NPs in weakly acidic colloidal solution is limited between 1 nm and 50 nm. The laser irradiation duration shows negative correlation with the size of Se NPs and unobvious impact to the pH of the solution which both are essential to the high yield of Cu1.8Se NPs. Before Cu sheet is exhausted, Se colloidal solution can be successively added without influences to the product quality and the Se conversion rate. Such green methodology positively showcases a brand-new and potential strategy for mass production of Cu2 – x Se nanomaterials.

High-performance electromagnetic interference shielding and thermoelectric conversion derived from multifunctional Bi2Te2.7Se0.3/MXene composites

High-performance electromagnetic interference (EMI) materials with remarkable thermoelectric conversion/self-powered capabilities seem to be predictably imperative to eliminate electromagnetic wave pollution and reduce local overheating of devices to ensure the reliable operation of electronic instruments and wearable electronic devices. Herein, multifunctional Bi2Te2.7Se0.3/Ti3C2Tx (BTS/MXene) composites are fabricated by mixing BTS and MXene dispersion followed by vacuum-assisted filtration and hot pressing, which exhibit highest EMI shielding efficiency (EMI SE) of 94.33 dB and average EMI SE of 83.4 dB over the whole X band (BTS/MX-30, containing 30 wt% MXene). Meanwhile, the BTS/MXene composites also demonstrate impressive thermoelectric (TE) conversion capabilities, achieving a peak dimensionless figure of merit (ZT) of 1.2 from 313 to 498 K for BTS/MX-1.5 (involving 1.5 wt% MXene). The excellent electromagnetic wave shielding performances originate from the reflection caused by the impedance mismatch, the multiple scattering at the BTS/MXene interface, the polarization at the terminal of MXene and BTS, etc. On the other hand, the excellent thermoelectric performance of BTS/MXene comes from the high conductivity of MXene and the blocking of low-energy carriers and the scattering of phonons at the interface. Hence, multifunctional BTS/MXene composites display broad prospects for simultaneous implementation of EMI shielding and thermoelectric conversion/self-powered applications in miniature and wearable electronic instruments.

In-situ pulse electropolymerization of pyrrole on single-walled carbon nanotubes for thermoelectric composite materials

Electrochemical polymerization has become a powerful tool for constructing high-performance thermoelectric (TE) composite films, and attracted great attention from researchers. To date, however, there has been no report on the in-situ electrochemical polymerization of pyrrole (Py) on single-walled carbon nanotubes (SWCNTs). In this work, we developed a series of high-performance polypyrrole (PPy)/SWCNT composites by the in-situ pyrrole electropolymerization on the pre-fabricated SWCNT membrane electrode, where a pulse galvanostatic electropolymerization (PGEP) technology was adopted to perfect TE performance of the PPy/SWCNT composites via the interface engineering. As a result, the optimized PPy/SWCNT composite film achieved an excellent TE performance, with the largest power factor (PF) of 365.2 ± 9.6 μW m−1 K−2 and the maximum figure of merit (ZT) of 0.203 ± 0.005 at room temperature, which is well beyond the reach of the PPy-based binary TE composite materials reported previously. This work suggested that in-situ pulse electropolymerization would be an effective and feasible strategy for constructing high-performance TE materials, and also opened a new, promising avenue for improving TE materials in the future.

Full-Electrochemical Construction of High-Performance Polypyrrole/Tellurium Thermoelectrical Nanocomposites.

As one of the most attractive inorganics to improve the thermoelectric (TE) performance of the conducting polymers, tellurium (Te) has received intense concern due to its superior Seebeck coefficient (S). However, far less attention has been paid to polypyrrole (PPy)/Te TE composites to date. In this work, we present an innovative full-electrochemical method to architect PPy/Te TE composite films by sequentially depositing Te with large S and PPy with high electrical conductivity (σ). Consequently, the PPy/Te composite films achieved excellent TE performance, with the largest power factor (PF) reaching up to 234.3 ± 4.1 μW m-1 K-2. To the best of our knowledge, this value approaches the reported highest PF record (240.3 ± 5.0 μW m-1 K-2) for PPy-based composites. This suggests that the modified full-electrochemical method is a feasible and effective strategy for achieving high-performance TE composite films, which would probably provide a general guideline for the design and preparation of excellent TE materials in the future.

Tuning the Carrier Scattering Mechanism by Rare-Earth Element Doping for High Average zT in Mg3Sb2-Based Compounds.

Mg3Sb2-based compounds are promising thermoelectric materials because of their excellent thermoelectric performance, low cost, and good mechanical properties. In this work, Er, Dy, Gd, and Nd are all confirmed to be effective n-type dopants for optimizing the carrier concentration, increasing the density of states effective mass, and suppressing the ionized impurity scattering of Mg3Sb2-based compounds. By increasing the sintering temperature, a larger grain size can be achieved and can effectively improve the carrier mobility in the whole measured temperature range. As a result, maximum zT values above ∼1.6 at 673 K and average zTs above ∼1.0 between 300 and 673 K were achieved for Mg3.07Er0.03Bi0.5Sb1.5, Mg3.07Dy0.03Bi0.5Sb1.5, and Mg3.07Nd0.03Bi0.5Sb1.5. In addition, a high compressive strength of ∼180 MPa was obtained in Mg3.07Dy0.03Bi0.5Sb1.5. Therefore, rare-earth element-doped Mg3Sb2-based compounds are promising for thermoelectric applications.

Electronic structure and thermal conductance of the MASnI3/Bi2Te3 interface: a first-principles study

To develop high-performance thermoelectric devices that can be created using printing technology, the interface of a composite material composed of MASnI3 and Bi2Te3, which individually show excellent thermoelectric performance, was studied based on first-principles calculations. The structural stability, electronic state, and interfacial thermal conductance of the interface between Bi2Te3 and MASnI3 were evaluated. Among the interface structure models, we found stable interface structures and revealed their specific electronic states. Around the Fermi energy, the interface structures with TeII and Bi terminations exhibited interface levels attributed to the overlapping electron densities for Bi2Te3 and MASnI3 at the interface. Calculation of the interfacial thermal conductance using the diffuse mismatch model suggested that construction of the interface between Bi2Te3 and MASnI3 could reduce the thermal conductivity. The obtained value was similar to the experimental value for the inorganic/organic interface.

High Thermoelectric Performance Achieved in Sb-Doped GeTe by Manipulating Carrier Concentration and Nanoscale Twin Grains.

Lead-free and eco-friendly GeTe shows promising mid-temperature thermoelectric applications. However, a low Seebeck coefficient due to its intrinsically high hole concentration induced by Ge vacancies, and a relatively high thermal conductivity result in inferior thermoelectric performance in pristine GeTe. Extrinsic dopants such as Sb, Bi, and Y could play a crucial role in regulating the hole concentration of GeTe because of their different valence states as cations and high solubility in GeTe. Here we investigate the thermoelectric performance of GeTe upon Sb doping, and demonstrate a high maximum zT value up to 1.88 in Ge0.90Sb0.10Te as a result of the significant suppression in thermal conductivity while maintaining a high power factor. The maintained high power factor is due to the markable enhancement in the Seebeck coefficient, which could be attributed to the significant suppression of hole concentration and the valence band convergence upon Sb doping, while the low thermal conductivity stems from the suppression of electronic thermal conductivity due to the increase in electrical resistivity and the lowering of lattice thermal conductivity through strengthening the phonon scattering by lattice distortion, dislocations, and twin boundaries. The excellent thermoelectric performance of Ge0.90Sb0.10Te shows good reproducibility and thermal stability. This work confirms that Ge0.90Sb0.10Te is a superior thermoelectric material for practical application.

Review on grain size effects on thermal conductivity in ZnO thermoelectric materials.

Thermoelectric materials have recently attracted a lot of attention due to their ability to convert waste heat into electricity. Based on the extensive research in this area, the nanostructuring approach has been viewed as an effective strategy for increasing thermoelectric performance. This approach focuses on the formation and growth of the superfine, pure and uniform grain size. Since the grain size has a strong influence on the thermal conductivity, this can be reduced by increasing the phonon scattering at grain boundaries and refining the grain sizes. Therefore, this review aims to discuss the mechanism of reduction in thermal conductivity in small-grain zinc oxide (ZnO) and the optimization techniques for obtaining ZnO nanoparticles with desirably low thermal conductivity and excellent thermoelectric performance.

Two-dimensional penta-like PdPSe with a puckered pentagonal structure: a first-principles study.

Low-symmetry penta-PdPSe (Pd4P4Se4) with intrinsic in-plane anisotropy was synthesized successfully [P. Li et al., Adv. Mater., 2021, 2102541]. Motivated by this experimental discovery, we investigate the structural, mechanical, electronic, optical and thermoelectric properties of PdPSe nanosheets via density functional theory calculations. The phonon dispersion, molecular dynamics simulation, and cohesive energy mechanical properties of the penta-PdPSe are verified to confirm its stability. The phonon spectrum represents a striking gap between the high-frequency and the low-frequency optical branches and an out-of-plane flexure mode with a quadratic dispersion in the long-wavelength limit. The Poisson's ratio indicates that penta-PdPSe is a brittle nanosheet. The penta-PdPSe is a semiconductor with an indirect bandgap of 1.40 (2.07) eV using the PBE functional (HSE06 hybrid functional). Optical properties simulation suggests that PdPSe is capable of absorbing a substantial range of visible to ultraviolet light. Band alignment analysis also reveals the compatibility of PdPSe for water splitting photocatalysis application. By combining the electrical and thermal transport properties of PdPSe, we show that a high power factor is achievable at room temperature, thus making PdPSe a candidate material for thermoelectric applications. Our findings reveal the strong potential of penta-PdPSe nanosheets for a wide array of applications, including optoelectronic, water splitting and thermoelectric device applications.

Highly tailored gap-like structure for excellent thermoelectric performance

A pioneering regulation was offered to tune the structural density and size in gap-like Sb2Te3(GeTe)n for excellent thermoelectric performance.

β-Ga2O3: a potential high-temperature thermoelectric material.

The thermoelectric properties of intrinsic n-type β-Ga2O3 are evaluated by first-principles calculations combined with Boltzmann transport theory and relaxation time approximation. The electron mobility is predicted by considering polar optical phonon scattering in β-Ga2O3. A temperature power law of T-0.67 is obtained for the intrinsic electron mobility. Due to the ultra-wide band gap of 4.7-4.9 eV, β-Ga2O3 has a large Seebeck coefficient. As a result, a maximum power factor of 3.1 × 10-3 W m-1 K-2 is obtained at 1600 K. A clear anisotropy in lattice thermal conductivity is observed, with the highest thermal conductivity of 23.1 W m-1 K-1 at 300 K along the [010] direction, and a lower value of 13.2 and 12.2 W m-1 K-1 along the [001] and [100] directions, respectively. A high ZT value of 1.07 at 1600 K can be obtained at the optimal carrier concentration of 2.4 × 1019 cm-3, which is superior to that of most other oxides such as ZnO. In addition, the lattice thermal conductivity can be reduced by precisely adjusting the grain size, and the lattice thermal conductivity at 300 K (1600 K) can be reduced by 73% (39%) when the grain size is decreased to 10 nm. The excellent thermoelectric properties of β-Ga2O3 have promoted its potential application in the field of high temperature thermoelectric conversion.

Significantly (00l)-textured Ag2Se thin films with excellent thermoelectric performance for flexible power applications

A flexible n-type Ag2Se thin film with a high power factor (PF) of 21.6 μW cm−1 K−2 and a ZT value over 0.6 was successfully prepared by a facile self-assembled growth method.

Multistage nanostructures induced by precursor phase spontaneous partitioning lead to an excellent thermoelectric performance in Cu1.8S0.8Se0.2

Multiscale nanostructures and nano-defects significantly increase the ZT of Cu1.8S0.8Se0.2 thermoelectric material.

Effect of evolution for dispersed phase on thermoelectric performance of Yb0.2(CoSb2.875Te0.125)4

CoSb3-based skutterudites, as a medium-temperature thermoelectric material, show excellent thermoelectric performance, but high thermal conductivity suppresses the high ZT value. Here, x% SnTe/Yb0.2(CoSb2.875Te0.125)4 samples were synthesized through vacuum melting reaction and spark plasma sintering (SPS). With increasing of SnTe content, the dispersed phase CoSb2, SnTe and CoTe2 appear successively via a selection of nucleation kinetics for 1%, 3% and 5% SnTe composited sample. Due to scattering of the dispersed phase and the solid solution distortion, lattice conductivity (κlat) of the 3% SnTe/Yb0.2(CoSb2.875Te0.125)4 sample decreases from 1.55 W m−1 K−1 to 1.19 W m−1 K−1 compared with the Yb0.2(CoSb2.875Te0.125)4 sample, which reduces by ∼22.8% at 773 K. The maximum thermoelectric merit ZT of the 3% SnTe/Yb0.2(CoSb2.875Te0.125)4 sample achieves 1.18 at 773 K.