Weiqiang Zhou

Liquid Exfoliated Graphene as Dopant for Improving the Thermoelectric Power Factor of Conductive PEDOT:PSS Nanofilm with Hydrazine Treatment

UNLABELLEDnHere, we fabricated a highly conductive poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (nnnPEDOTnPSS) nanofilm via vacuum filtration with enhanced thermoelectric power factor by doping of liquid exfoliated graphene (GE) and hydrazine treatment. The effect of GE exfoliated in dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) on the electrical conductivity and thermopower ofnnnPEDOTnPSS was investigated. Although electrical conductivity decreased with increasing GE, thermoelectric power factors ofnnnPEDOTnPSS nanofilms were improved with 3 wt % GE in DMF (38.6 μW m(-1) K(-2)) and in NMP (28.0 μW m(-1) K(-2)) compared to purennnPEDOTnPSS (11.5 μW m(-1) K(-2)). The mechanism of improvement was proposed to be the removal of PSS and the good interaction between PEDOT and GE. With hydrazine treatment, 3 wt % GE-dopednnnPEDOTnPSS nanofilm (PG3) showed a further enhanced power factor of 53.3 μW m(-1) K(-2) (∼5 times higher than that of pristinennnPEDOTnPSS nanofilm). The effects of hydrazine containing concentration, treatment time, and temperature on the electrical conductivity and Seebeck coefficient of PG3 were investigated systematically. An estimated thermoelectric figure of merit (ZT) is 0.05 with the optimized power factor at room temperature.

Use of organic solvent-assisted exfoliated MoS2 for optimizing the thermoelectric performance of flexible PEDOT:PSS thin films

For organic thermoelectric materials, a main challenge is to achieve high electrical conductivity and a large Seebeck coefficient, in order to improve the power factor. Here we suggest a simple way to address this issue through the addition of a small amount of liquid-phase exfoliated MoS2 nanosheets into poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) solutions by direct vacuum filtration. The effects of exfoliated MoS2 nanosheets in common organic solvents on the thermoelectric properties of PEDOT:PSS were investigated. The organic solvent-assisted exfoliated MoS2 nanosheet solution was found to play an important role in improving the thermoelectric performance of the PEDOT:PSS thin film. Common organic solvents effectively removed some of the PSS during the formation of the film, resulting in a significantly enhanced electrical conductivity (1250 S cm−1) for the PEDOT:PSS/MoS2 (PM) thin film. On the other hand, the introduction of MoS2 nanosheets in PEDOT:PSS led to a slight increase of the Seebeck coefficient from 14.5 to 19.5 μV K−1 without a significant reduction of the electrical conductivity of the PM thin film. An optimized power factor of 45.6 μW m−1 K−2 was achieved for the PM thin film with 4 wt% MoS2 exfoliated in an N,N-dimethylformamide (DMF) solution. The exfoliated MoS2 nanosheets in DMF exhibited a better effect on the thermoelectric performance of the PM composites than did those in other organic solvents. The method used here suggests a novel strategy for improving both electrical conductivity and the Seebeck coefficient, and hence optimizing the thermoelectric performance of the PEDOT:PSS thin film.

Facile Fabrication of PEDOT:PSS/Polythiophenes Bilayered Nanofilms on Pure Organic Electrodes and Their Thermoelectric Performance

A pure organic PEDOT:PSS nanofilm was used as a working electrode for the first time to electrodeposit polymer films of polythiophene (PTh) and its derivatives in a boron trifluoride diethyl ether (BFEE) solution, fabricating a novel generation of bilayered nanofilms. Cyclic voltammetry (CV) demonstrated good electrochemical stability of the as-formed films. Structures and surface morphologies were systematically investigated by the characterizations of cross-section SEM, FT-IR, UV-vis, SEM, and AFM. The resulting films revealed stable and enhanced thermoelectric (TE) performances. The electrical conductivity values of PEDOT:PSS/PTh, PEDOT:PSS/P3MeT, and PEDOT:PSS/P3HT nanofilms were determined to be 123.9, 136.5, and 200.5 S cm(-1), respectively. The power factor reached up to be a maximum value of 5.79 μW m(-1) k(-2). Thus, this technique offers a facile approach to a class of bilayered nanofilms, and it may provide a general strategy for fabricating a new generation of conducting polymers for more practical applications.

Highly electrical and thermoelectric properties of a PEDOT:PSS thin-film via direct dilution–filtration

Herein, a rapid and robust method for a highly conductive PEDOT:PSS thin-film has been developed by direct dilution–filtration with common organic solvents. A large electrical conductivity of 1500 S cm−1 has been achieved and a high thermoelectric figure of merit (ZT ∼ 0.1) makes it a promising organic thermoelectric candidate.

High-performance capacitive behavior of layered reduced graphene oxide and polyindole nanocomposite materials

In this work, a high-capacitance hybrid nanocomposite based on reduced graphene oxide (RGO) and polyindole (PIn) was fabricated via an in situ chemical oxidative polymerization approach. The structure and morphology of PIn/RGO were investigated by FT-IR, Raman spectroscopy, SEM and TEM. The electrochemical properties of this electrode in aqueous H2SO4 electrolyte were also investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS). Compared to RGO and PIn electrodes, the PIn/RGO hybrid nanocomposite shows a large improved specific capacitance of 322.8 F g−1 at 1.0 A g−1, good stability with a cycling efficiency of 94.5% after 1000 cycles, and high energy density of 36 W h kg−1 at a high power density of 5000 W kg−1. The enhanced performance is proposed to arise from the synergetic effect between PIn and RGO. In addition, the symmetric PIn/RGO//PIn/RGO supercapacitor showed specific capacitance of 99.8 F g−1 and only 3.7% decay after 1000 cycles. These results imply that PIn/RGO should be a promising electrode material for supercapacitor applications.

Electrosynthesis and electrochemical capacitive behavior of a new nitrogen PEDOT analogue-based polymer electrode

In this work, poly(N-methyl-3,4-dihydrothieno[3,4-b][1,4]oxazine) (PMDTO), a new nitrogen poly(3,4-ethylendioxythiophene) (PEDOT) analogue, was synthesized by an electrochemical deposition method, and the capacitive properties of PMDTO were investigated and compared with those of PEDOT. The structure and morphology of PMDTO were characterized by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The pseudocapacitive properties of the as-prepared PMDTO electrodes have been examined by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) measurements and electrochemical impedance spectroscopy (EIS) in 0.1 mol L−1 CH3CN–Bu4NBF4 electrolyte solution. The as-prepared PMDTO electrode showed a high specific capacitance of 154.3 F g−1 at a discharge current density of 3 A g−1 and exhibited cycling stability with the maximal capacitance retention of nearly 71% after 500 cycles at a high current density of 10 A g−1. Additionally, the asymmetrical supercapacitor based on PMDTO and PEDOT electrodes exhibited a maximum specific capacitance of 63.5 F g−1 and an energy density of 12.7 W h kg−1 at a power density of 0.59 kW kg−1. These results implied that the PMDTO electrode can be used as a potential electrode material for supercapacitors.

One-step template-free electrodeposition of novel poly(indole-7-carboxylic acid) nanowires and their high capacitance properties

Poly(indole-7-carboxylic acid) (PICA) nanowires with conductivity of 5 × 10−2 S cm−1 were prepared by a facile, one-step and template-free electrodeposition method. The hydrogen bond interactions between the N–H group and the carboxyl group facilitated the formation of PICA nanowires. The diameter of the PICA nanowires was about 40 nm confirmed by scanning electron microscopy. Fourier transformation infrared spectroscopy and 1H NMR spectroscopy confirmed that the polymerization occurred at the C2 and C3 position on the indole ring. The electrochemical capacitance properties of the PICA nanowires were investigated with cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscope techniques. A remarkable specific capacitance of 373.2 F g−1 was obtained at a current density of 2.5 A g−1 in 1.0 M H2SO4 solution. PICA nanowires presented an excellent cycle life with 91% specific capacitance retention after 1000 charge–discharge processes. The energy density of the symmetric full cell based on two PICA electrodes was 7.03 W h kg−1 at a power density of 4500 W kg−1. These results implied that the PICA nanowires will be a promising electrode material for supercapacitors.

Thermoelectric performance of PEDOT:PSS/Bi2Te3-nanowires: a comparison of hybrid types

We herein compare the thermoelectric performance of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and Bi2Te3 nanowires (Bi2Te3-NWs) composites (PEDOT:PSS/Bi2Te3-NWs) including layer-by-layer assembly and hybrid structures by drop-cast as well as pellets. The Bi2Te3 nanowires are synthesized by a wet-chemical method. The hybrid PEDOT:PSS/Bi2Te3-NWs film with 10xa0wt% Bi2Te3-NWs has a higher electrical conductivity (401 S cm−1) and power factor (10.6xa0μWxa0m−1xa0K−2) than that of layer-by-by layer assembly film. The Seebeck coefficient keeps mostly unchangeable for hybrid films as the increasing Bi2Te3-NWs which is different from layered films. The PEDOT:PSS/Bi2Te3-NWs pellets have a larger Seebeck coefficient (54xa0μVxa0K−1) with a lower electrical conductivity (12.4 S cm−1) leading a lower power factor. The hybrid method for preparation of PEDOT:PSS/Bi2Te3-NWs film is a more efficient way for the enhancement of thermoelectric performance.

Transparent 1T-MoS2 nanofilm robustly anchored on substrate by layer-by-layer self-assembly and its ultra-high cycling stability as supercapacitors

Two-dimensional MoS2 materials have attracted more and more interest and been applied to the field of energy storage because of its unique physical, optical, electronic and electrochemical properties. However, there are no reports on high-stable transparent MoS2 nanofilms as supercapacitors electrode. Here, we describe a transparent 1T-MoS2 nanofilm electrode with super-long stability anchored on the indium tin oxide (ITO) glass by a simple alternate layer-by-layer (LBL) self-assembly of a highly charged cationic poly(diallyldimethylammonium chloride) (PDDA) and negative single-/few-layer 1T MoS2 nanosheets. The ITO/(PDDA/MoS2)20 electrode shows a transmittance of 51.6% at 550 nm and obviously exhibits excellent transparency by naked eye observation. Ultrasonic damage test validates that the (PDDA/MoS2)20 film with the average thickness about 50 nm is robustly anchored on ITO substrate. Additionally, the electrochemical results indicate that the ITO/(PDDA/MoS2)20 film shows areal capacitance of 1.1 mF cm-2 and volumetric capacitance of 220 F cm-3 at 0.04 mA cm-2, 130.6% retention of the original capacitance value after 5000 cycles. Further experiments indicate that the formation of transparent (PDDA/MoS2) x nanofilm by LBL self-assembly can be extended to other substrates, e.g., slide glass and flexible polyethylene terephthalate (PET). Thus, the easily available (PDDA/MoS2) x nanofilm electrode has great potential for application in transparent and/or flexible optoelectronic and electronics devices.

Functionalized Poly(3,4-ethylenedioxy bithiophene) Films for Tuning Electrochromic and Thermoelectric Properties

Conductive thiophene-based polymers have garnered great attention for use in organic electron materials such as electrochromic and thermoelectric materials. However, they suffer from poor electron transport properties and long-term stability, leading to limited development eventually. Here, we proposed a strategy of functionalized thiophene-based polymers with oligo(ethylene glycol) or alkyl side chains and synthesized a series of poly(3,4-ethylenedioxy bithiophene)s (PEDTs) to tune their electrochromic and thermoelectric properties. An alkyl group bearing electronic ability at the thiophene ring effectively achieved a large increase in the electrical conductivity with nearly invariable Seebeck coefficient, resulting in an enhancement by 1 order of magnitude for the thermoelectric power factor. Moreover, the electrochromic properties of functionalized PEDTs gained an effective improvement in the optical contrast and coloration efficiency as well as stability with multicolor changes between neutral and oxidized states. The functionalized PEDTs can be proposed as an alternative strategy to tune the electrochromic and thermoelectric properties for organic polymer materials.