Poly(3,4-ethylenedioxythiophene)/Te/Single-Walled Carbon Nanotube Composites with High Thermoelectric Performance Promoted by Electropolymerization

Thermoelectrics and thermocells for fire warning applications

Historically, fire disasters have killed numerous human lives, and caused tremendous property loss. Fire warning systems play a vital role in predicting fire risks, and are strongly desired to effectively prevent the disaster occurrence and significantly reduce the loss. Among the developed fire warning systems, thermoelectrics (TEs) and thermocells (TECs)-based fire warning materials are extremely important and indispensable in future research, owing to their unique capability of direct conversion between heat and electricity. Here, we present this review of the recent progress of TEs and TECs in fire warning field. Firstly, a brief introduction of existing fire warning systems is provided, including the mechanisms and features of various types. Then, the mechanisms of electronic TE (eTE), ionic TE (iTE) and TEC are elucidated. Next, the basic principles for the material preparation and device fabrication are discussed in their dimension sequence. Subsequently, some important advances or examples of TE fire warnings are highlighted in details. Finally, the challenges and prospects are outlooked.

Compositing Benzothieno[3,2-b]Benzofuran Derivatives with Single-Walled Carbon Nanotubes for Enhanced Thermoelectric Performance

Although numerous thermoelectric (TE) composites of organic materials and single-walled carbon nanotubes (SWCNTs) have been developed in the past decade, most of the research has been related to polymers without much on organic small molecules (OSMs). In this work, benzothieno[3,2-b]benzofuran (BTBF) and its derivatives (BTBF-Br and BTBF-2Br) were synthesized and their TE composites with SWCNTs were prepared. It is found that the highest molecular orbital level and band gap (Eg) of BTBF, BTBF-Br, and BTBF-2Br gradually decrease upon the introduction of electron-withdrawing Br group on BTBF. These changes significantly improve the Seebeck coefficient and power factor (PF) of OSM/SWCNT composites. An appropriate energy barrier between BTBF-2Br and SWCNTs promotes the energy filtering effect, which further contributes to the enhancement of composites' thermoelectric properties. The composites of SWCNTs and BTBF-2Br with the smallest Eg (4.192 eV) afford the best thermoelectric performance with the room temperature power factor of 169.70 ± 3.46 μW m-1 K-2 in addition to good mechanical flexibility and thermal stability. This study provides a feasible strategy for the preparation of OSM/SWCNT composites with improved thermoelectric properties.

One-pot synthesis and versatile applications of recyclable aminal-linked dynamic framework

A recyclable polyhemiaminal dynamic network (PHDN) and its composites were prepared via in situ polymerization. The obtained versatile materials is promising for high-performance functional thermosetting materials and electrochemical active materials.

Polymers based on thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide by CH–CH arylation reaction for high-performance thin-film transistors

Three homopolymers were successfully synthesized by direct CH–CH arylation polymerization of thieno[3,4-c]pyrrole-4,6-dione or pyromellitic diimide derivatives affording highly purified polymers with high molecular weights (43.0–174.7 K). Thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide derivatives are considered as electron-withdrawing units. The synthesized homopolymers P1, P2, and P3 showed band gaps in the range of 2.13–2.08 eV, respectively. The electron mobilities of the three homopolymers have been investigated. The thin film transistor for P1 prepared by the eutectic-melt-assisted nanoimprinting method achieved an electron mobility of 2.11 × 10⁻³ cm² s⁻¹ V⁻¹. Based on the obtained results, the synthesized polymers can be used as potential electron acceptors in solar cell applications.

The homopolymers P1, P2 and P3 were successfully synthesized by direct CH–CH arylation polymerization in an eco-friendly one-step coupling reaction. They present n-type properties for potential applications as acceptor polymers.

Thermal Degradation Behavior of Epoxy Resin Containing Modified Carbon Nanotubes

Via the surface-grafting of carbon nanotubes (CNTs) with a silicon-containing flame retardant (PMDA), a novel flame retardant CNTs-PMDA was synthesized. The flame retardancy was tested by cone calorimeter. Compared with pure epoxy resin, the total heat release (THR) and peak heat release rate (PHRR) of epoxy resin containing CNTs-PMDA were significantly reduced, by 44.6% and 24.6%, respectively. Furthermore, thermal degradation behavior of epoxy resin based composite was studied by the thermogravimetric analysis with differences in heating rates. The kinetic parameters of the thermal degradation for epoxy resin composites were evaluated by the Kissinger method and Flynn-Wall-Ozawa method. The results suggested that activation energy values of epoxy resin containing CNTs-PMDA in thermal degradation process were higher than those of pure epoxy resin in the final stage of the thermal degradation process, which was closely related to the final formation of char layer residues. Finally, the results from Dynamic mechanical thermal analysis (DMTA) and Scanning electron microscopy (SEM) measurements exhibited that the functionalization of CNTs with PMDA obviously improved the dispersion of CNTs in the epoxy resin matrix.

Flame Retardancy and Dispersion of Functionalized Carbon Nanotubes in Thiol-Ene Nanocomposites

A polysilicone flame retardant (PA) was synthesized and covalently grafted onto the surface of carbon nanotubes (CNTs) via amide linkages to obtain modified CNTs (CNTs-PA). The grafting reaction was characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectrometer (XPS), Transmission electron microscopy (TEM) and Thermogravimetric analysis (TGA), and the resultant CNTs-PA was soluble and stable in polar solvents Chloroform. Thiol-ene (TE)/CNTs-PA nanocomposites were prepared via Ultraviolet curing. The flame retardancy of thiol-ene nanocomposites was improved, especially for the heat release rate. Moreover, the results from Scanning electron microscopy (SEM) and Dynamic mechanical thermal analysis (DMTA) showed that the CNTs-PA improved the dispersion of CNTs in thiol-ene and enhanced the interfacial interaction between CNTs-PA and thiol-ene matrix.

Organic/Inorganic Hybrid Boosting Energy Harvesting Based on the Photothermoelectric Effect

Attracted by the capability of light to heat and electricity conversion, the photothermoelectric (PTE) effect has drawn great attention in the field of energy conversion and self-powered electronics. However, it still requires effective strategies to convert electricity from light based on the corresponding photothermoelectric generator. Herein, considering the broad photoresponse and large Seebeck effect of tellurium nanowires (Te NWs) as well as the high electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), PEDOT:PSS/Te NW hybrid thin films were fabricated to enhance the conversion efficiency by the photothermoelectric effect with respect to single thermoelectric performance. A detailed comparison has been achieved between the photothermoelectric and thermoelectric properties induced by light illumination and heating plates through current-voltage (I-V) transport, respectively. PEDOT:PSS/Te NW hybrid films also show an enhanced photothermal harvesting compared to pure PEDOT:PSS. A photothermoelectric device was assembled based on the as-fabricated PEDOT:PSS/Te NW hybrid films with 90 wt% Te NWs and achieved a competitive output power density with good stability, which may provide insights into improving solar energy harvesting-based photothermoelectric conversion by organic/inorganic hybrids.

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.

Synergistically Boosting Thermoelectric Performance of PEDOT:PSS/SWCNT Composites via the Ion-Exchange Effect and Promoting SWCNT Dispersion by the Ionic Liquid

Poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is perhaps the most successful polymer material for thermoelectric (TE) applications. So far, treatments by high-boiling solvents, acid or base, or mixing with the carbon nanotube (CNT) are the main ways to improve its TE performance. Herein, we report the synergistically boosting TE properties of PEDOT:PSS/single-walled CNT (SWCNT) composites by the ionic liquid (IL). The composites are prepared by physically mixing the SWCNT dispersion containing the IL with PEDOT:PSS solution and subsequent vacuum filtration. The IL additive has two major functions, that is, inducing the phase separation of PEDOT:PSS and a linear quinoid conformation of PEDOT and promoting the SWCNT dispersion. The maximum power factor at room temperature reaches 182.7 ± 9.2 μW m^-1 K^-2 (the corresponding electrical conductivity and Seebeck coefficient are 1602.6 ± 103.0 S cm^-1 and 33.4 ± 0.4 μV K^-1, respectively) for the free-standing flexible film of the PEDOT:PSS/SWCNT composites with the IL, which is much higher than those of the pristine PEDOT:PSS, the IL-free PEDOT:PSS/SWCNT, and the SWCNT films. The high TE performance of composites can be ascribed to synergistic roles of the ion-exchange effect and promotion of SWCNT dispersion by the IL. This work demonstrates the dual roles for the IL in regulating each component of the PEDOT:PSS/SWCNT composite that synergistically boosts the TE performance.

Enhancing Thermoelectric Performance of Polyaniline/Single-Walled Carbon Nanotube Composites via Dimethyl Sulfoxide-Mediated Electropolymerization

The fabrication of flexible high-performance organic/inorganic thermoelectric (TE) composite films has been a hot spot for researchers in recent years. In this work, dynamic 3-phase interfacial electropolymerization of aniline, together with physical mixing with single-walled carbon nanotubes (SWCNTs), was adopted to prepare polyaniline/SWCNT (PANI/SWCNT) TE composites. The dimethyl sulfoxide (DMSO) added into the electrochemical polymerization system affords strong capability in improving the TE performance of composite films. Moreover, varying loadings of SWCNTs can also conveniently tune the TE performance of composites. Hence, the resultant composites afford the highest power factor (PF) of 236.4 ± 5.9 μW m^-1 K^-2 at room temperature. This work demonstrates that the introduction of DMSO into the electrolyte and the electrochemical polymerization are highly effective in fabricating high-performance PANI/SWCNT TE composites.

Boosting the Power Factor of Benzodithiophene Based Donor-Acceptor Copolymers/SWCNTs Composites through Doping

In this study, a benzodithiophene (BDT)-based donor (D)–acceptor (A) polymer containing carbazole segment in the side-chain was designed and synthesized and the thermoelectric composites with 50 wt % of single walled carbon nanotubes (SWCNTs) were prepared via ultrasonication method. Strong interfacial interactions existed in both of the composites before and after immersing into the 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ) solution as confirmed by UV-Vis-NIR, Raman, XRD and SEM characterizations. After doping the composites by F₄TCNQ, the electrical conductivity of the composites increased from 120.32 S cm⁻¹ to 1044.92 S cm⁻¹ in the room temperature. With increasing the temperature, the electrical conductivities and Seebeck coefficients of the undoped composites both decreased significantly for the composites; the power factor at 475 K was only 6.8 μW m⁻¹ K⁻², which was about nine times smaller than the power factor at room temperature (55.9 μW m⁻¹ K⁻²). In the case of doped composites, although the electrical conductivity was deceased from 1044.9 S cm⁻¹ to 504.17 S cm⁻¹, the Seebeck coefficient increased from 23.76 μV K⁻¹ to 35.69 μW m⁻¹ K⁻², therefore, the power factors of the doped composites were almost no change with heating the composite films.