In situ chemical oxidative polymerization preparation of poly(3,4-ethylenedioxythiophene)/graphene nanocomposites with enhanced thermoelectric performance

Structural modulation induced by cobalt-based ionic liquids for enhanced thermoelectric transport in PEDOT:PSS

Poly(3,4ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) has been intensively studied for its thermoelectric applications. Structural modulation to improve crystalline ordering, chain conformation and film morphology is a promising way to decouple the trade-off between conductivity and Seebeck coefficient and thus improve the thermoelectric power factor. Post treatment with ionic liquid ([CoCl₂  ⋅ 6H₂ O]:[ChCl]) bearing cobalt-containing anions resulted in a remarkable enhancement of the power factor to 76.8 μW m^-1  K^-2 . This IL combines the influence of a high-boiling polar organic solvent and diffusing ions. A high σ mainly resulted from the efficient removal of PSS chains, ordering of the structure and delocalization of bipoloran-dominant transport after conformational change. The increase in S was not due to dedoping of PEDOT chains, but rather the sharp feature of the density of states at the Fermi level induced by ion-exchange with unconventional anions.

Thermoelectric Materials for Textile Applications

Since prehistoric times, textiles have served an important role-providing necessary protection and comfort. Recently, the rise of electronic textiles (e-textiles) as part of the larger efforts to develop smart textiles, has paved the way for enhancing textile functionalities including sensing, energy harvesting, and active heating and cooling. Recent attention has focused on the integration of thermoelectric (TE) functionalities into textiles-making fabrics capable of either converting body heating into electricity (Seebeck effect) or conversely using electricity to provide next-to-skin heating/cooling (Peltier effect). Various TE materials have been explored, classified broadly into (i) inorganic, (ii) organic, and (iii) hybrid organic-inorganic. TE figure-of-merit (ZT) is commonly used to correlate Seebeck coefficient, electrical and thermal conductivity. For textiles, it is important to think of appropriate materials not just in terms of ZT, but also whether they are flexible, conformable, and easily processable. Commercial TEs usually compromise rigid, sometimes toxic, inorganic materials such as bismuth and lead. For textiles, organic and hybrid TE materials are more appropriate. Carbon-based TE materials have been especially attractive since graphene and carbon nanotubes have excellent transport properties with easy modifications to create TE materials with high ZT and textile compatibility. This review focuses on flexible TE materials and their integration into textiles.

Flexible Thermoelectric Materials and Generators: Challenges and Innovations

The urgent need for ecofriendly, stable, long-lifetime power sources is driving the booming market for miniaturized and integrated electronics, including wearable and medical implantable devices. Flexible thermoelectric materials and devices are receiving increasing attention, due to their capability to convert heat into electricity directly by conformably attaching them onto heat sources. Polymer-based flexible thermoelectric materials are particularly fascinating because of their intrinsic flexibility, affordability, and low toxicity. There are other promising alternatives including inorganic-based flexible thermoelectrics that have high energy-conversion efficiency, large power output, and stability at relatively high temperature. Herein, the state-of-the-art in the development of flexible thermoelectric materials and devices is summarized, including exploring the fundamentals behind the performance of flexible thermoelectric materials and devices by relating materials chemistry and physics to properties. By taking insights from carrier and phonon transport, the limitations of high-performance flexible thermoelectric materials and the underlying mechanisms associated with each optimization strategy are highlighted. Finally, the remaining challenges in flexible thermoelectric materials are discussed in conclusion, and suggestions and a framework to guide future development are provided, which may pave the way for a bright future for flexible thermoelectric devices in the energy market.

In Situ Oxidation Synthesis of p-Type Composite with Narrow-Bandgap Small Organic Molecule Coating on Single-Walled Carbon Nanotube: Flexible Film and Thermoelectric Performance

Although composites of organic polymers or n-type small molecule/carbon nanotube (CNT) have achieved significant advances in thermoelectric (TE) applications, p-type TE composites of small organic molecules as thick surface coating layers on the surfaces of inorganic nanoparticles still remain a great challenge. Taking advantage of in situ oxidation reaction of thieno[3,4-b]pyrazine (TP) into TP di-N-oxide (TPNO) on single-walled CNT (SWCNT) surface, a novel synthesis strategy is proposed to achieve flexible films of TE composites with narrow-bandgap (1.19 eV) small molecule coating on SWCNT surface. The TE performance can be effectively enhanced and conveniently tuned by poly(sodium-p-styrenesulfonate) content, TPNO/SWCNT mass ratio, and posttreatment by various polar solvents. The maximum of the composite power factor at room temperature is 29.4 ± 1.0 µW m^-1 K^-2 . The work presents a way to achieve flexible films of p-type small organic molecule/inorganic composites with clear surface coating morphology for TE application.

Copper-Phenylacetylide Nanobelt/Single-Walled Carbon Nanotube Composites: Mechanochromic Luminescence Phenomenon and Thermoelectric Performance

We report flexible films of organic-inorganic thermoelectric (TE) composites based on organometallic coordination compound [copper-phenylacetylide (PhC₂Cu)] nanobelts and single-walled carbon nanotubes (SWCNTs). Interestingly, an unusual mechanochromic luminescence phenomenon from bright green to dark red is clearly observed after grinding the PhC₂Cu crystalline nanobelts. The PhC₂Cu/SWCNT composites display high mechanical flexibility and excellent TE performance. The maximum power factor at room temperature can reach as high as 200.2 ± 10.9 μW m^-1 K^-2. The present study opens an avenue to fabricate novel organic-inorganic TE composite materials using organometallic coordination compounds such as PhC₂Cu.

Exploring High-Performance n-Type Thermoelectric Composites Using Amino-Substituted Rylene Dimides and Carbon Nanotubes

Taking advantage of the high electrical conductivity of a single-walled carbon nanotube (SWCNT) and the large Seebeck coefficient of rylene diimide, a convenient strategy is proposed to achieve high-performance n-type thermoelectric (TE) composites containing a SWCNT and amino-substituted perylene diimide (PDINE) or naphthalene diimide (NDINE). The obtained n-type composites display greatly enhanced TE performance with maximum power factors of 112 ± 8 (PDINE/SWCNT) and 135 ± 14 (NDINE/SWCNT) μW m^-1 K^-2. A short doping time of 0.5 h can ensure high TE performance. The corresponding TE module consisting of five p-n junctions reaches a large output power of 3.3 μW under a 50 °C temperature gradient. In addition, the n-type composites exhibit high air stability and excellent thermal stability. This design strategy benefits the future fabricating of high-performance n-type TE materials and devices.

Polypyrrole/Graphene/Polyaniline Ternary Nanocomposite with High Thermoelectric Power Factor

Polypyrrole/Graphene/Polyaniline (PPy/GNs/PANi) ternary nanocomposite with high thermoelectric power factor has been successfully prepared through the combination of in situ polymerization and solution process. FTIR, Raman spectra, XRD, and SEM analyses show the strong π-π interactions existed among PPy, GNs, and PANi, leading to the formation of more ordered regions in the composite. Both the in situ polymerization and solution process can enhance the dispersion homogeneity of graphene in the polymer matrix, bringing about increased nanointerfaces in the PPy/GNs/PANi composite. The thermoelectric properties of Polypyrrole/Graphene (PPy/GNs), Polyaniline/Graphene (PANi/GNs), and PPy/GNs/PANi composites are measured at different temperatures after being cold pressed. Consequently, the PPy/GNs/PANi composite with 32 wt % graphene demonstrates optimal electrical conductivity, Seebeck coefficient and extremely high power factor of up to 52.5 μ W m^-1 K^-2, which is almost 1.6 × 10³ times, 1.4 × 10³ times, 2.7 times, and 3.6 times higher than those of the pure PANi, pure PPy, PPy/GNs composite, and PANi/GNs composite, respectively.

Engineered Molecular Chain Ordering in Single-Walled Carbon Nanotubes/Polyaniline Composite Films for High-Performance Organic Thermoelectric Materials

Single-walled carbon nanotubes (SWNTs)/polyaniline (PANI) composite films with enhanced thermoelectric properties were prepared by combining in situ polymerization and solution processing. Conductive atomic force microscopy and X-ray diffraction measurements confirmed that solution processing and strong π-π interactions between the PANI and SWNTs induced the PANI molecules to form a highly ordered structure. The improved degree of order of the PANI molecular arrangement increased the carrier mobility and thereby enhanced the electrical transport properties of PANI. The maximum in-plane electrical conductivity and power factor of the SWNTs/PANI composite films reached 1.44×10(3)  S cm(-1) and 217 μW m(-1)  K(-2) , respectively, at room temperature. Furthermore, a thermoelectric generator fabricated with the SWNTs/PANI composite films showed good electric generation ability and stability. A high power density of 10.4 μW cm(-2)  K(-1) was obtained, which is superior to most reported results obtained in organic thermoelectric modules.

PEDOT-based composites as electrode materials for supercapacitors

Poly (3, 4-ethylenedioxythiophene) (denoted PEDOT) already has a brief history of being used as an active material in supercapacitors. It has many advantages such as low-cost, flexibility, and good electrical conductivity and pseudocapacitance. However, the major drawback is low stability, which means an obvious capacitance drop after a certain number of charge-discharge cycles. Another disadvantage is its limited capacitance and this becomes an issue for industrial applications. To solve these problems, there are several approaches including the addition of conducting nanofillers to increase conductivity, and mixing or depositing metal oxide to enhance capacitance. Furthermore, expanding the surface area of PEDOT is one of the main methods to improve its performance in energy storage applications through special processes; for example using a three-dimensional substrate or preparing PEDOT aerogel through freeze drying. This paper reviews recent techniques and outcomes of PEDOT based composites for supercapacitors, as well as detailed calculations about capacitances. Finally, this paper outlines the new direction and recent challenges of PEDOT based composites for supercapacitor applications.

Preparation, characterization, and chemical-induced hydrophobicity of thermostable amine-modified graphene oxide

A small molecule was grafted onto the graphene oxide surfaces using two different approaches and the obtained amine-modified graphene oxides have excellent thermal stability and significantly enhanced water/air contact angles.

Recent advances in graphene/polyamide 6 composites: a review

This paper reviews recent years’ (2009–2015) advances in graphene/PA6 nanocomposites for the first time.

Design and fabrication of hollow and filled graphene-based polymeric spheres via core–shell electrospraying

Two dimensional graphene oxide sheets are converted into three dimensional (3D) hollow and filled microspheres by using three different carrying polymers through one-step core–shell electrospraying technique without applying any post treatments.