High-performance Thermoelectric Composites Research Articles

High-performance thermoelectric composites via scalable and low-cost ink processing

This work demonstrates a remarkable room-temperature figure of merit zT of 1.3 for BiSbTe-based composites with excellent reproducibility using a scalable, low-cost ink processing technique.

Enhanced Thermoelectric Properties of Composites Prepared With Poly(3,4-Ethylenedioxythiophene) Poly(Styrenesulfonate) and Vertically Aligned Se Wire.

Controlling the electronic transport behavior in thermoelectric composites is one of the most promising approaches to enhance their power factor because this enables decoupling of the correlation between the electrical conductivity and Seebeck coefficient. Herein, we show that the unexpected high power factor of the Se nanowire array embedded in poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) can be achieved by controlling the interfacial band structure engineering. The electrical conductivity and Seebeck coefficient simultaneously increased, confirming that the synthesis of organic/inorganic hybrid thermoelectric materials with improved performance was possible. Our exploration can be helpful for the rational design of high-performance thermoelectric composites through interface engineering.

N-Type Flexible Films and a Thermoelectric Generator of Single-Walled Carbon Nanotube-Grafted Tin Selenide Nanocrystal Composites.

Despite the significant progress in thermoelectric composites in recent years, the enhancement of thermoelectric performance is mainly based on weak interfacial interactions, although strong interactions (such as covalent-bonding grafting) are expected to display a more significant effect. In this study, the thermoelectric composites are prepared using a covalent-bond grafting method between tin selenide (SnSe) and single-walled carbon nanotubes (SWCNTs) via a simple solvothermal process. The as-prepared highly flexible composite film shows an n-type thermoelectric characteristic. An optimized power factor of 58.86 μW m-1 K-2 at room temperature has been realized for the composite film with 16 wt % SWCNT loading. Finally, a flexible thermoelectric generator (TEG) consisting of three couples of p/n films is assembled, which can generate an open-circuit voltage of 15.55 μV and a maximum output power of 1.38 μW at a temperature gradient of 60 K. The results open a new avenue for the fabrication of n-type flexible films and TEG based on covalent-bonding-grafted composites and will benefit the design strategy of high-performance thermoelectric composites and flexible TEGs.

Feasibility of using chemically exfoliated SnSe nanobelts in constructing flexible SWCNTs-based composite films for high-performance thermoelectric applications

Despite the significant progress in thermoelectric composites in recent years, composite systems completely composed of one-dimensional (1D) and two-dimensional (2D) nanostructures are rarely reported. In this study, the thermoelectric composites are prepared using 2D nanobelts of SnSe, obtained by a chemically exfoliation process (solvothermal lithium-intercalation and subsequent exfoliation), and 1D single-walled carbon nanotubes (SWCNTs) via a facile solution mixing and subsequent vacuum filtration method. The thermoelectric performance of the SnSe nanobelt/SWCNT composite films are further improved by post-treatment of thermal annealing. An optimized power factor at room temperature of 145 ± 28 μW m−1 K−2 for the composite film with 80 wt% SWCNTs has been realized, which is much higher than that of either component. The results inspire a new insight into the SnSe-related thermoelectric composites, laying a foundation for the fabrication of high-performance thermoelectric composites in the future.

Pseudo in situ construction of high-performance thermoelectric composites with a dioxothiopyrone-based D-A polymer coating on SWCNTs.

Organic polymer/inorganic particle composites with thermoelectric (TE) properties have witnessed rapid progress in recent years. Nevertheless, both development of novel polymers and optimization of compositing methods remain highly desirable. In this study, we first demonstrated a simulated in situ coagulation strategy for construction of high-performance thermoelectric materials by utilizing single-walled carbon nanotubes (SWCNTs) and a new D–A polymer TPO-TTP12 that was synthesized via incorporating dioxothiopyrone subunit into a polymeric chain. It was proven that the preparation methods have a significant influence on thermoelectric properties of the TPO-TTP12/SWCNT composites. The in situ prepared composite films tend to achieve much better thermoelectric performances than those prepared by simply mixing the corresponding polymer with SWCNTs. As a result, the in situ compositing obtains the highest Seebeck coefficient of 66.10 ± 0.05 μV K−1 at the TPO-TTP12-to-SWCNT mass ratio of 1/2, and the best electrical conductivity of up to 500.5 ± 53.3 S cm−1 at the polymer/SWCNT mass ratio of 1/20, respectively; moreover, the power factor for the in situ prepared composites reaches a maximum value of 141.94 ± 1.47 μW m−1 K−2, far higher than that of 104.68 ± 0.86 μW m−1 K−2 for the by-mixing produced composites. This indicates that the dioxothiopyrone moiety is a promising building block for constructing thermoelectric polymers, and the simulated in situ compositing strategy is a promising way to improve TE properties of composite materials.

Boosting thermoelectric performance by in situ growth of metal organic framework on carbon nanotube and subsequent annealing

Despite the significant progress in thermoelectric composites in the last five years, examining the existing main body of publications shows the scarcity of composite systems and limited preparation strategies. Metal-organic frameworks (MOFs) have been extensively studied and have wide applications, however, MOF-related thermoelectric composites have been seldom reported mainly due to their poor electrical conductivity. In this work, we propose a conceptual strategy, in situ growing reaction and subsequent annealing, to achieve zeolitic imidazolate framework 67/carbon nanotube (ZIF-67@CNT) composites with a unique microstructure of MOFs growing on CNT surfaces. The ZIF-67@CNT composites display outstanding and tunable thermoelectric properties. Annealing plays an important role in the composite morphology, structure and thermoelectric performance. Both the electrical conductivity (825.7 ± 12.0 S cm−1) and the figure of merit (ZT = ∼0.02) at room temperature are the highest in the experimental data reported so far for MOF-related materials, and even comparable to the corresponding theoretical values. The results inspire a new insight into MOF-related thermoelectric composites, which should be considered for future design strategies for novel high-performance thermoelectric composites.

Toward high thermoelectric performance for polypyrrole composites by dynamic 3-phase interfacial electropolymerization and chemical doping of carbon nanotubes

Polymer thermoelectric composites have received significant attention in recent years. To achieve high thermoelectric performance is one main aim, especially when being compared with their inorganic counterparts. Here, we report high-performance thermoelectric composites based on single-walled carbon nanotube (SWCNT) and polypyrrole (PPy), which are prepared by dynamic 3-phase interfacial electropolymerization and subsequent physical mixing. We found that both SWCNT content and chemical doping of SWCNT dramatically affected the composite thermoelectric performance. The maximum power factor at room temperature of the PPy composite reaches as high as 240.3 ± 5.0 μW m−1 K−2, which may be the highest value for PPy and its composites reported so far. The present study demonstrates that the dynamic 3-phase interfacial electropolymerization combining SWCNT chemical doping is effective to fabricate high-performance polymer thermoelectric composites.

Boosting the Adhesivity of π-Conjugated Polymers by Embedding Platinum Acetylides towards High-Performance Thermoelectric Composites.

Single-walled carbon nanotubes (SWCNTs) incorporated with π-conjugated polymers, have proven to be an effective approach in the production of advanced thermoelectric composites. However, the studied polymers are mainly limited to scanty conventional conductive polymers, and their performances still remain to be improved. Herein, a new planar moiety of platinum acetylide in the π-conjugated system is introduced to enhance the intermolecular interaction with the SWCNTs via π–π and d–π interactions, which is crucial in regulating the thermoelectric performances of SWCNT-based composites. As expected, SWCNT composites based on the platinum acetylides embedded polymers displayed a higher power factor (130.7 ± 3.8 μW·m−1·K−2) at ambient temperature than those without platinum acetylides (59.5 ± 0.7 μW·m−1·K−2) under the same conditions. Moreover, the strong interactions between the platinum acetylide-based polymers and the SWCNTs are confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements.

High performance p-type organic thermoelectric materials based on metalloporphyrin/single-walled carbon nanotube composite films

Single-walled carbon nanotube/organic small molecule based thermoelectric materials have attracted significant scientific attention in recent years. However, up to now, no detailed thermoelectric study reported is focused on the single-walled carbon nanotube/organometallic complex composite films. By considering the excellent properties of tetraphenylporphyrin (such as its π-conjugated system, versatile structure and stability) and the important roles of metal ions in improving thermoelectric properties, metalloporphyrins manifest great potential as composites for single-walled carbon nanotubes. Hence, in this work, we first propose a convenient strategy to obtain high-performance thermoelectric composites containing metalloporphyrin molecules and single-walled carbon nanotubes. It is found that the single-walled carbon nanotube/ZnTPP composite film demonstrates the best thermoelectric performance with a maximum power factor of 247.2 μWm−1K−2 at 340 K, which is perhaps one of the highest thermoelectric power factors reported for single-walled carbon nanotube/organic small molecule-based p-type materials. Three p-type materials exhibit outstanding electric conductivities with a maximum of 1028.7 S cm−1 (single-walled carbon nanotube/CuTPP at 340 K). Furthermore, the produced thermoelectric materials manifest outstanding air stability and thermostability. Therefore, our proposed method can be a promising reference for fabricating novel p-type high-performance thermoelectric materials using metalloporphyrin-based building blocks.

Topological doping effects in 2D chalcogenide thermoelectrics

The topological nature of two-dimensional (2D) chalcogenide platelets, can present novel opportunities in thin, flexible thermoelectrics. In this work, metal dopants are added to the reactive edges of 2D Bi2Te3 platelets. We show that along this active edge, an atomically well-ordered heterojunction is formed and facile charge exchange is created, onto the platelet and proximal to its known topological states. Temperature dependent conductivity suggests that local band bending across the interface may act as an injection energy filter for dopant-originated carriers. Moreover, as carrier density increases with increasing edge-dopant, carrier scattering does not appear to increase dramatically. As a result, an apparent decoupling between electrical conductivity and Seebeck coefficient occurs, leading to a surprisingly high power factors (PF): For example, the PF increases in Bi2Te3 platelets by eight times when doped with Cu. First principles calculations show that the electronics of the semiconductor-metal interfaces are quite different for edge and facial configurations, thus the site of metal dopant is believed to play an important role in the expected thermoelectric performance. Finally, this work suggests that the topological sensitivity of dopant placement should be considered in the rational design of high performance thermoelectric composites.

Tailoring the framework of organic small molecule semiconductors towards high-performance thermoelectric composites via conglutinated carbon nanotube webs

Regulating the structure of p-type organic small molecules to generate thermoelectric composites for achieving a high power factor of 113.2 μW m−1 K−2.

High temperature thermoelectric properties of skutterudite-Bi2Te3 nanocomposites

Nanocomposite engineering has been proved effective in diverse regimes of material research to attain a performance beyond each constituent phase. In this work, Yb-filled CoSb3 (bulk matrix/host)-Bi0.4Sb1.6Te3 (secondary inclusion) thermoelectric nanocomposites have been synthesized via an ex situ process. Bi0.4Sb1.6Te3 inclusions are mainly distributed at the grain boundaries of Yb0.2Co4Sb12 matrix in the composites. In particular, Te diffuses in situ from Bi0.4Sb1.6Te3 through Yb0.2Co4Sb12 matrix during the hot pressing process. This, combined with the grain boundary effect, results in favorable changes in the carrier concentration, carrier mobility, electrical resistivity, Seebeck coefficient, and thermal conductivity. Such synergistic changes are notably absent in the stand-alone Te-doped Yb-filled CoSb3, suggesting the key role of diffusion and grain boundaries. As a result, a maximum ZT value of 0.96 has been attained for Yb0.2Co4Sb12-2 wt% Bi0.4Sb1.6Te3 at 650 K. The present work opens a new avenue towards high performance thermoelectric composites via controlled inter-constituent diffusion and grain boundary effect.

Carbon nanotube bundles/polystyrene composites as high-performance flexible thermoelectric materials

Lightweight and flexible thermoelectric devices consisting of carbon nanotube (CNT)-based materials have the potential to be used for the various applications, such as energy harvesting from the low-temperature waste heat that exists ubiquitously in living areas. Because high-performance CNT-based materials are crucial for the broad-ranging employment of CNT-based thermoelectric devices, considerable efforts are being made to improve the power-generation capability of CNT-based thermoelectric materials. Here, we report high-performance thermoelectric composites consisting of CNT bundles and polystyrene fabricated by a planetary ball milling-based dispersion technique, which allows for the direct dispersion of the CNT bundles within the polystyrene matrix without causing the disaggregation of the bundled CNTs into individual ones. The CNT-bundles/polystyrene composites reported here exhibit a power factor of 413 μW/K2·m.