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Similarly to polyanilines, polypyrroles, and polythiophenes, polyindoles belonging to the fused-ring family have emerged in the past several decades as promising materials due to their unique physical and electrochemical properties. To date, polyindoles have been studied in over 200 scientific publications. These studies revealed that the materials based on polyindoles could have an important influence on electrochromic devices, sensors, catalysis and electro-catalysis, anticorrosion, diodes, supercapacitors, batteries, and biology-related applications. The aim of this review is to provide an overview of the development of polyindoles with regard to synthesis, polymerization mechanisms, copolymers, composites, properties, and applications, and reflect on the related existing challenges and make notes on future perspectives. [ABSTRACT FROM PUBLISHER]

Free-standing conductive films are important for the application in organic electronics. However, PEDOT as one of the most promising CPs is difficult to be prepared into free-standing paper. Herein, a novel EDOT derivative, 1,6-bis((2,3-dihydrothieno[3,4- b ][1,4]dioxin-2-yl)methoxy)hexane (BEDTH), was synthesized and easily electrodeposited into free-standing flexible conducting poly(1,6-bis((2,3-dihydrothieno[3,4- b ][1,4]dioxin-2-yl)methoxy)hexane) (PBEDTH) in CH 2 Cl 2 containing 0.1 M Bu 4 NBF 4 . The free-standing PBEDTH films with the conductivity of 0.11 S cm −1 were characterized by FT-IR, UV–vis, SEM, TG, dynamic mechanical analysis and electrochemical method, respectively. Electrochemical results indicated that the specific capacitance of PBEDTH film was 40.8 F g −1 at the current density of 0.5 A g −1 in ionic liquid BmimBF 4 with the cycling capacitance retention of 86.7% after 5000 cycles. Additionally, the thermoelectric property of free-standing flexible PBEDTH film was also studied, showing the Seebeck coefficient was 37.2 μV K −1 and the power factor was 0.015 μW K −2 m −1 at 300 K. Although the capacitive and thermoelectric performance is not satisfactory, the free-standing flexible PBEDTH films will still be promising in the areas of energies and sensors in the true sense. [ABSTRACT FROM AUTHOR]

In this paper, poly[poly( N-vinyl-carbazole)] (PPVK) films electrodeposited in tetrahydrofuran (THF) containing 12 % boron trifluoride diethyl etherate (BFEE) were studied as electrode active material for supercapacitors. The morphology and thermal property were characterized by SEM, atomic force microscopy (AFM), and thermogravimetry (TG), respectively. The electrochemical capacitive behaviors of the PPVK films were also investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The electrochemical results showed that the specific capacitance of PPVK films in CHCN solution was about 126 mF cm at 1.5 mA cm and the capacitance retention was only 14.4 % after 1000 cycles. It was exciting to improve the specific capacitance up to 169.3 mF cm at 1.5 mA cm and to make the cyclic stability increase to 81.8 % capacitance retention after 5000 cycles when the equivalent BFEE was added into the CHCN solution containing 0.05 M BuNBF electrolyte. These results clearly demonstrated that BFEE was an efficient promoter for the enhancement of the capacitance performance of PPVK films. Therefore, with the help of BFEE electrolyte, the PPVK films have potential application as capacitive materials in high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Many researches involving in the solvent treatment of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) have been carried out for enhancing the electric conductivity. Herein, the capacitive performance of commercial PEDOT:PSS (trade name: PH1000) treated by NMP, EG and DMSO solvents were studied, including their conductivity, morphology, surface roughness and surface composition. Compared with pristine PH1000 film, the electrochemical active windows of the solvent-treated PH1000 films were negatively shifted to about −0.8 V from 0 V, and more excitedly, the operating voltage of all-solid-state symmetrical supercapacitors based on the treated PH1000 films could enhance up to 1.8 V from about 1.2 V with an excellent stability during 2500 charge/discharge cycles. Moreover, the effects of the three solvents on the capacitive performance of devices were compared in detail, which discovered that the device built with DMSO-treated PH1000 showed superior capacitance behaviors. [ABSTRACT FROM AUTHOR]

The development of asymmetric supercapacitors (ASCs) with high power and energy density is greatly restricted by the low capacitance of the anode materials. V2O5 is a promising anode material with high theoretical capacity, but its low conductivity and high dissolution are not conducive to applications in energy storage. Herein, oxygen-vacancy PEDOT/V2O5 ultrathin nanosheets with a thickness of about 4.4 nm are fabricated by the oxidative polymerization of EDOT monomers on V2O5 nanosheets in the absence of other oxidants. The results of XPS and EPR confirm that the polymerization of PEDOT increases the oxygen vacancy concentration of V2O5. The PEDOT/V2O5 nanosheets exhibit a specific capacitance of 406 F g−1 at 2 mV s−1 and excellent cyclic stability in the mixed organic electrolyte of dimethyl carbonate and ethylene carbonate. The energy density of ASCs composed of PEDOT/V2O5 as the anode and activated carbon as the cathode reaches 65 W h kg−1 at a power density of 1490 W kg−1. This means that PEDOT/V2O5 has enormous potential in high-energy storage. [ABSTRACT FROM AUTHOR]

Supercapacitors are widely used in various fields due to their high power density, fast charging and discharging speeds, and long service life. However, with the increasing demand for flexible electronics, integrated supercapacitors in devices are also facing more challenges, such as extensibility, bending stability, and operability. Despite many reports on stretchable supercapacitors, challenges still exist in their preparation process, which involves multiple steps. Therefore, we prepared stretchable conducting polymer electrodes by depositing thiophene and 3-methylthiophene on patterned 304 stainless steel (SS 304) through electropolymerization. The cycling stability of the prepared stretchable electrodes could be further improved by protecting them with poly(vinyl alcohol)/sulfuric acid (PVA/H2SO4) gel electrolyte. Specifically, the mechanical stability of the polythiophene (PTh) electrode was improved by 2.5%, and the stability of the poly(3-methylthiophene (P3MeT) electrode was improved by 7.0%. As a result, the assembled flexible supercapacitors maintained 93% of their stability even after 10,000 cycles of strain at 100%, which indicates potential applications in flexible electronics. [ABSTRACT FROM AUTHOR]

The rapid development of current wearable electronics motivates the promotion of energy storage devices. Supercapacitor with flexible, lightweight, highly efficient, and long cycling life is one of the potential and glittering candidates. Here, the composite film of carboxylated graphene (CG) and commercially available poly (3, 4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) are prepared as electrodes for flexible electrochemical capacitors by ultrasonication and vacuum filtration. The CG/PEDOT:PSS films were roundly characterized by SEM, XPS, FTIR, XRD and Raman spectrometer. The as-prepared free-standing films exhibited high specific capacitance (192.7 F g-1 at 0.5 A g-1), excellent rate capability (up to 80.4% from 0.5 to 20 A g-1), and good electrochemical stability (95.5% of specific capacitance retention after 50000 cycles). Surprisingly, the post treated free-standing films by Dimethyl Formamide (DMF) shows better capacitive properties than those of the pristine electrode, such as higher specific capacitance (204.3 F g-1 at 0.5 A g-1), and ultralong-cycling stability (104.6% retention at a high current density of 20 A g-1 after 50000 cycles). It is expected that the free-standing CG/PEDOT:PSS films can be used as flexible electrodes for various wearable energy storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ce-doped WO 3 nanowire arrays flexible electrodes were grown on carbon cloth. • Ce doping increases the oxygen vacancies and expands the lattice spacing. • The ASC exerts 31.7 Wh kg−1 of energy density when the power density is 700 W kg−1. • Assembled two flexible soft-packaged ASCs can light up LEDs and timers. Tungsten trioxide (WO 3) is recognized as a promising anode material for asymmetric supercapacitors (ASCs), yet its low conductivity and stability as well as energy density greatly limit its development. Herein, a flexible Ce-doped WO 3 (Ce 1.5% -WO 3) nanowire array with rich oxygen vacancies is grown on carbon cloth by a solvothermal synthesis. The specific capacitance of Ce 1.5% -WO 3 is 493F g−1 at 4 A/g and remains 90.4 % after 5000 cycles, superior to that of WO 3 nanowire arrays (416F g−1, 80.3 %). The improved performance mainly stems from the synergistic effects of more oxygen vacancies, higher specific surface area, wider lattice spacing, faster ion diffusion, and electron transport generated by Ce doping. As-prepared ASC device can reach an energy density of 31.7 Wh kg−1 at a power density of 700 W kg−1. Furthermore, two flexible soft-packaged ASCs connected in series can illuminate different electronic devices. This strategy proves the great application prospect of Ce-doped WO 3 nanowire arrays flexible electrodes in supercapacitors. [ABSTRACT FROM AUTHOR]

Asymmetric supercapacitors (ASC) meet the high power and energy demand in energy storage devices; however, the low capacitance of the anode materials severely hinders the development of ASCs. MoO3 with its high theoretical capacity is an ideal anode material, but its low electrical conductivity limits the application of capacitive energy storage. Herein, abundant oxygen vacancies Ce‐doped MoO3 (OV‐MoO3/Ce) ultrathin nanoflakes anode materials with a thickness of 1.51‐2.01 nm are constructed by a simple hydrothermal method. It is found that the nanostructure of MoO3 can be controllably changed from thick nanobelts into ultrathin nanoflakes by adjusting the Ce doping concentration. And Ce doping in the OV‐MoO3 lattice can additionally introduce abundant oxygen vacancies without introducing Ce oxide and other impurities. Benefiting from the synergy of ample oxygen vacancies, high specific surface area, and accelerated ion diffusion and charge mobility, the optimized OV‐MoO3/Ce electrode achieves a high specific capacitance (1439.0 F g‐1 at 2 mV s‐1 and 1446.3 F g‐1 at 5 A g‐1) and good cycle stability. More impressively, the ASC assembled using optimized OV‐MoO3/Ce as anode materials can provide an ultrahigh energy density of 150.0 Wh kg‐1 at a power density of 800 W kg‐1, and the practical demonstration of the assembled ASC device highlights its great potential for high energy storage. [ABSTRACT FROM AUTHOR]

• The CG/NiO composite electrode is prepared by electrostatic self-assembly. • NiO nanosheets cover the surface of the carboxylated graphene sheets. • The addition of CG increases the BET surface area of NiO by three times. • The CG/NiO composite electrode has a capacity of 175.5 C g−1 at 1 A g−1. Nickel oxide (NiO) with the advantages of inexpensive, non-toxic, environmentally friendly and high theoretical specific capacitance, is a potential electrode material for supercapacitors. In this work, the synthesized NiO exhibited a stacked state of nanosheets with wavy patterns and a high specific surface area. Additionally, the carboxylated graphene/nickel oxide (CG/NiO) composite electrodes were prepared through the electrostatic self-assembly technique. The CG/NiO composite electrode was systematically characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscope, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller measurements. More excitingly, the BET surface area of the CG/NiO composite electrode is 138.14 m2/g, which is three times higher than that of the pure NiO. The high surface area and unique mesoporous structure of composite electrodes facilitated rapid ion transport and sufficient redox reactions. As a result, the CG/NiO composite electrode displayed a high specific capacity of 175.5 C g−1 at 1 A/g and satisfying cycling stability (55.4 % retention after 5000 cycles at 5 A/g). [ABSTRACT FROM AUTHOR]

Wearable energy storage device nowadays gains great interest due to sharply increased demand for highly flexible, stretchable and embedded electronics, where fiber-based supercapacitor (FSC) is a competitive counterpart. The poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)/ polyaniline (PEDOT:PSS/PANi) fiber has been prepared via an accessible technique of one-dimensional (1D) self-assembly. Nevertheless, PSS as the main cross-linking matrix may lead to more hopping sites for charge carriers, lessening the continuous electrically conductive path. Herein, PEDOT:PSS/PANi fiber was treated with dimethyl sulfoxide (DMSO) to remove the insulative PSS chains. Coupling high electroactivity of PANi and high conductivity of PEDOT, the optimized DMSO-PEDOT:PSS/PANi fiber displays enhanced electrochemical properties with a high specific capacitance (Cs) of 367.7 F g−1 at 0.5 A g−1 and good rate capability. Moreover, a symmetric FSC based on the DMSO-P4P6 fiber exhibits a high energy density of 42.4 Wh kg−1 at a power density of 302.3 W kg−1. PEDOT: PSS/PANi fibers are prepared via a simple technique of one-dimensional (1D) self-assembly, and the PEDOT: PSS/PANi fiber exhibits superior flexibility, electrical conductivity, and electrochemical properties. [ABSTRACT FROM AUTHOR]

Fluorination of conjugated polymers has been explored as a viable strategy for enhancing the overall performance of corresponding polymers. In this work, two trifluoromethylated polyindoles (5-PFMIn and 6-PFMIn) are synthesized via simple electropolymerization and applied as energy storage materials for supercapacitors. Spectroscopic, morphological, thermal stability, and electrochemical analyses of trifluoromethylated polyindoles and their non-fluorinated counterparts (5-PMIn and 6-PMIn) are performed to reveal the significant effect of the trifluoromethyl group on the properties of polymers. Compared with non-fluorinated counterparts, 5-PFMIn and 6-PFMIn show rougher morphologies and higher thermal stabilities, and more interestingly, the fluorination of polyindoles results in substantial improvement of their electrochemical behavior. The specific capacitances of 5-PFMIn and 6-PFMIn are found to be 269 F g−1 and 296 F g−1 at 10 A g−1, respectively with excellent cycling stability of about 90% after 5000 cycles, which are superior to those of their counterparts, 5-PMIn (75 F g−1, 73%) and 6-PMIn (178 F g−1, 70%). The promising trifluoromethylated polyindoles demonstrate high potential for electrochemical capacitor application. [ABSTRACT FROM AUTHOR]

Two electrochromic polymers based on thiophene–benzene derivatives were prepared using an electrochemical method and exhibited multiple separate redox couples due to the introduction of side chains. The energy storage states of electrochromic supercapacitors based on the resulting polymers could be monitored by their appearance colour. [ABSTRACT FROM AUTHOR]

Substitution effects significantly impact the electropolymerization, morphology, properties and electrochemical performance of conducting polymers. In this work, the substitution effects of the electron-withdrawing cyano group on indole polymers are studied in detail. Polyindole (PIn) and its three cyano group substituted derivatives, i.e. , poly(5-cyanoindole) (P5CIn), poly(6-cyanoindole) (P6CIn), and poly(7-cyanoindole) (P7CIn), are successfully electrosynthesized in 0.1 M LiClO 4 /acetonitrile, while it is difficult to electrodeposit 4-cyanoindole into polymer due to the steric effects. Scanning electron microscopic images reveal that P5CIn, P6CIn, and P7CIn have nanofiber structures, while PIn has a dense and cracked structure. Furthermore, P5CIn displays the best capacitance performance with a specific capacitance of 493 F g-1 at 2.5 A g-1, and 87.1% capacitance retention after 5000 cycles charge/discharge. A detailed study of cyano-substituted PIn is provided by this work and it also presents a kind of high-performance supercapacitor material. • The substitution effects of cyano group on indole polymers are studied in detail. • Three kinds of polyindoles are successfully electrosynthesized. • The new polymers show excellent supercapacitor performance. [ABSTRACT FROM AUTHOR]

Layered WS 2 nanosheet has advantages in the application of energy devices because of its distinctive structure and high electrochemical behaviors. The fabrication of high-quality free-standing WS 2 film is anticipant and challenging in developing its flexible and miniature device. Here, using a highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as binder, flexible free-standing WS 2 /PEDOT:PSS film as miniature supercapacitors electrode materials was easily prepared by vacuum filtration method. The WS 2 /PEDOT:PSS film was characterized by scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, Raman spectrum, X-ray photoelectron spectroscopy and electrochemical technology. The free-standing WS 2 /PEDOT:PSS film with conductivity of 44 S cm −1 showed a good flexibility, robustly mechanical property and high electrochemical behaviors. The flexible film can bear 300 g weight and be used as a conducting wire in a circuit. The WS 2 /PEDOT:PSS film with thickness of ~2.1 μm exhibited high areal capacitance of 86 mF cm −2 and volumetric capacitance of 411 F cm −3 at 40 mV s −1 in 1.0 M H 2 SO 4 solution. Besides, the capacitance retention could reach 107% of initial specific capacitance after 5000 charge-discharge cycles. Moreover, the flexible device based on WS 2 /PEDOT:PSS films could be assembled without any substrates and showed a volumetric capacitance of 87 F cm −3 at 10 mV s −1 and 86% capacitance retention of initial specific capacitance after 5000 cycles. These results implied the flexible free-standing WS 2 /PEDOT:PSS film has a potential application in flexible and miniature supercapacitors without any other substrates as current collectors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Capsaicin modified N-doped graphene (Cap-NG) is prepared by hydrothermal method. • Cap prevents the stacking of NG by non-covalently functionalization. • Cap improves the specific capacitance of NG to 312F g−1 at 1 A g−1. • Cap-NG shows an excellent cycle stability of 102.9 % after 10,000 cycles. Organic molecules with multi-electron redox active centers exhibit great potential in electrochemical storage. Immobilizing them on the graphene surface through π-π interaction can effectively improve the pseudocapacitance. Nature capsaicin (Cap) molecule, with redox active sites, is good benefit for enhance the capacitance performance of the nitrogen doped graphene (NG) by non-covalent modification. In this work, the Cap-functionalized NG (Cap-NG) is successfully prepared by one-step hydrothermal method combined with vacuum freeze-drying technology. The electrochemical measurements show that the optimal Cap-NG exhibits a high capacitance of 312 F g−1 at 1 Ag−1 and an excellent durable cycling life of 102.9 % after 10,000 charging/discharging cycle times at a current density of 20 Ag−1. Furthermore, the Cap-NG-based symmetrical supercapacitor (SSC) demonstrates an energy density of 8 Wh kg−1 at 596 W kg−1. Moreover, density functional theory (DFT) calculations are used to elaborate the origin of pseudocapacitance by researching the adsorption configuration, binding energy and charge storage mechanism of Cap on NG sheet as well as to calculate the density of states (Dos). This study further enriches the application of natural capsaicin molecule on energy storage, and provides another way to build a green and environment-friendly SCs. [ABSTRACT FROM AUTHOR]

Relative to those polymers based on thiophene, the polymers derived from planar symmetrical thieno[3,2- b ]thiophene moieties exhibit highly ordered crystalline, fast charge transport behaviors and good stability. Herein, the effects of the polymerization solvent, potential, and temperature on the structure, morphology, thermal stability and capacitive performance of the electrodeposited poly(thieno[3,2 -b ]thiophene) (PTT) film were studied by FT-IR, SEM, TG and electrochemical methods, respectively. It was found that the PTT film had a very high specific capacitance (627.5 F g −1 at 15 A g −1 ) in acetonitrile/0.1 M LiClO 4 , even at high current density of 100 A g −1 , its specific capacitance still reached 531 F g −1 . Additionally, the morphology and capacitance performance of PTT film were greatly affected by the polymerization solvent, potential, and temperature parameters. Therefore, it is believed that PTT can be a meaningful capacitive material if only the preparation condition is well optimized. [ABSTRACT FROM AUTHOR]

The poor conductivity of polyindole (PIn) is a major factor to limit its application in supercapacitors. To solve the problem, a simple and efficient immersion method designed to obtain a binary nanocomposite, which composed of polyindole hollow nanospheres (PIn-NS) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). PIn-NS with diameters of 300–600 nm and shell thickness of about 50 nm were prepared by the chemical oxidative polymerization of indole in the ethanol/H 2 O miscible solution using ammonium peroxydisulfate (APS) as oxidant agent without any surfactants. The pure PIn-NS modified carbon cloth (PIn-NS/CC) shows a low specific capacitance of 110 F g −1 at 0.5 A g −1 in 1.0 M H 2 SO 4 aqueous solution. By the immersion of PIn-NS/CC in PEDOT:PSS/ethanol solution, the obtained PIn-NS/CC-PEDOT:PSS shows a large improved specific capacitance of 623 F g −1 at 0.5 A g −1 and good stability with a cycling efficiency of 84.8% after 3000 cycles. The results demonstrate that the electrochemical properties of PIn-NS can be significantly improved with the assistance of PEDOT:PSS as electrically conductive connection. In addition, the symmetric PIn-NS/CC-PEDOT:PSS//PIn-NS/CC-PEDOT:PSS supercapacitor showed a high specific capacitance of 161 F g −1 at 0.5 A g −1 and the low equivalent series resistances (ESR) of 4.4 ohm. Therefore, such binary composite is a promising material for application in the next generation high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Large-scale chloromethyl functionalized poly(3,4-ethylenedioxythiophene) nanowires (PEDOT-MeCl), poly(2-chloromethyl-2,3-dihydrothieno[3,4- b ][1,4]dioxine), were easily electrodeposited in acetonitrile solution containing 0.1 M lithium perchlorate without any templates. The PEDOT-MeCl nanowires were characterized by FT-IR, TG, SEM, TEM and electrochemical technologies. The nanowires structural PEDOT-MeCl with diameter of about 20 nm displayed good thermal stability and high specific capacitance of 174 F g −1 at 25 mV s −1 . Furthermore, the energy density of the symmetric supercapacitor built by PEDOT-MeCl nanowires reached 6.95 Wh kg −1 at a power density of 1625 W kg −1 , and the specific capacitance retention was 81% after 1000 cycles. The above information implied the bright prospect of the PEDOT-MeCl nanowires as electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

• A machine learning strategy was applied for electrochemical sensor and supercapacitor. • The carbonized metal–organic framework showed excellent electrochemical response for niclosamide (NA) and good capacitance. • Both adsorption and binding energy were theoretically calculated and the structure of prepared material was optimized. Machine learning (ML) plays an important role in the electrochemical application of electrode materials. In this work, an emerging machine learning strategy for both electrochemical sensor and supercapacitor using carbonized metal–organic framework (C-ZIF-67) is proposed. The morphology and element analysis of C-ZIF-67 are characterized and further demonstrate the presence of C, N, O, Co elements. The ML model based on artificial neural network (ANN) algorithm as a powerful tool to realize intelligent analysis of niclosamide (NA), the derivative technique as an auxiliary means of voltammogram treatment to reduce personal error from data-reading and improve the sensitivity of electrochemical responses at very low concentrations, and the theoretical calculation is employed for both adsorption and binding energy, optimized structure of the prepared sensing material. The developed sensor displays excellent electrochemical response about 196.6-fold improvement compared with the bare GCE for NA, wider linear ranges of intelligent analysis from 1 nM to 9 μM with low limit of detection of 0.3 nM, and satisfactory practicability. ML model with ANN algorithm is also employed for predicting the performance of supercapacitor. The supercapacitor shows good performance with capacitance of 336.67 F/g at the current density of 2 A/g and excellent prediction with acceptable errors. This work will provide a new strategy for the development and electrochemical application of bifunctional electrode materials using the ML technique combined with theoretical calculation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Thieno[3,4- b ]-1,4-oxathiane (EOTT), one asymmetrical analog of 3,4-ethylenedioxythiophene (EDOT), was synthesized and its chemical oxidative polymerization was carried out in different solvents (dichloromethane, water, and acetonitrile (CH 2 Cl 2 , H 2 O, and ACN)). The effect of the solvent on the structure, crystalline characteristic, morphology, and thermal stability of poly(thieno[3,4- b ]-1,4-oxathiane) (PEOTT) were investigated by fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetry, respectively. PEOTT prepared from H 2 O exhibited higher electrical conductivity (∼10 0 S/cm) and more robust thermal stability. The electrochemical capacitance performance of PEOTT electrode in ACN–LiClO 4 was initially found dissatisfactory. Furthermore, the electrochemical properties of this electrode in another three aqueous electrolytes (H 2 SO 4 , HClO 4 , and LiClO 4 ) were also investigated comparatively by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS). It revealed the enhanced specific capacitance (208 F/g at 1 A/g) and improved capacitance retention (80.4% after 1000 cycles at 10 A/g) of PEOTT electrode in H 2 O–HClO 4 compared to those of the electrode in ACN–LiClO 4 . These results implied that PEOTT employing aqueous HClO 4 electrolyte should be a promising electrode material for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Aqueous poly(3,4-ethylenedioxythiophene methanol)-poly(styrene sulfonate) dispersion (PEDTM-PSS) was prepared by chemical oxidation synthesis. As-formed PEDTM-PSS film was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis, and scanning electron microscopy techniques. The results of Raman and FT-IR confirmed the formation of PEDTM-PSS. The electrochemical capacitance properties of PEDTM-PSS were firstly investigated in this paper by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscope techniques. PEDTM-PSS electrode showed a specific capacitance of 62.3 F g at a current density of 0.5 A g in 0.1 M LiClO/ACN solution, which was higher than the value of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) (50.5 F g). Furthermore, the energy density of assembled symmetric supercapacitor based on PEDTM-PSS was 2.4 Wh kg at a power density of 325 W kg, which was also higher than that of PEDOT-PSS (1.6 Wh kg). Most importantly, the symmetric supercapacitor exhibited extraordinary stability up to 1000 cycles with a specific capacitance retention of 105 %. These results indicated that the PEDTM-PSS was a promising electrode material for the supercapacitors application. [ABSTRACT FROM AUTHOR]

In this paper, the effects of carboxylic substituent position on their electrodeposition, morphology and capacitance properties were investigated for the first time. The results indicated that three carboxylic group substituted polyindole derivatives nanowires, namely poly(indole-5-carboxylic acid) (5-PICA), poly(indole-6-carboxylic acid) (6-PICA), and poly(indole-7-carboxylic acid) (7-PICA), were successfully electrochemically synthesized in acetonitrile containing 0.1 M LiClO 4 , whereas poly(indole-4-carboxylic acid) (4-PICA) was difficult to be obtained. For 5-PICA, 6-PICA and 7-PICA nanowires, the diameters of nanowires demonstrated by the scanning electron microscopy were about 100 nm, 50 nm, and 30 nm, respectively. Their specific capacitances and energy densities in 1.0 M H 2 SO 4 solution were measured to be 355 F g −1 , 383 F g −1 , 430 F g −1 at 2.5 A g −1 and 40.0, 43.1, 48.3 Wh kg −1 at a power density of 1125 W kg −1 , respectively, and their specific capacitance retentions after 1000 charge/discharge processes reached 94.5%, 95.1%, and 96%, respectively. These results indicated that the position of the carboxylic substituent had remarkable impacts on the diameter sizes and electrochemical properties of these polymer nanowires. Furthermore, the three polymers with high specific capacitance and excellent stability would be strong candidates as electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

In this work, poly(indole-5-carboxylic acid) (PICA) nanowires were facilely prepared by a one-step electrodeposition on glass carbon electrode (GC) and its capacitance performance was evaluated in different electrolytes. The initial galvanostatic charge/discharge test of PICA in acetonitrile/LiClO 4 exhibited a specific capacitance of 275 F g −1 at the current density of 1.0 A g −1 but the capacitance stability was quite poor, whereas, an enhanced specific capacitance (350 F g −1 at 1.0 A g −1 ) and an improved capacitance stability (98% capacitance retention after 1000 cycles) were obtained in HClO 4 aqueous electrolyte, which were also better than that in the counterpart media (Na 2 SO 4 , KCl, and H 2 SO 4 aqueous electrolytes). Additionally, the symmetrical supercapacitor based on two PICA electrodes in HClO 4 aqueous electrolyte exhibited a maximum specific capacitance of 69.0 F g −1 , an energy density of 9.4 Wh kg −1 at a power density of 1000 W kg −1 , and an excellent cycle life of 94% specific capacitance retention after 1000 cycles. These results implied that the PICA nanowires with HClO 4 aqueous solution as electrolyte will be a kind of promising electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

Poly(2,3-dihydrothieno[3,4- b ][1,4]dioxin-2-yl)methanol)/carbon fiber composite material (PDHDM/CF) was prepared via a simple electrodeposition method. The CF core and the PDHDM shell formed a 3-D PDHDM/CF core/shell structure composite. The PDHDM/CF was characterized by FT-IR spectroscopy, UV–vis spectra, SEM, cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscope techniques. Compared with the PDHDM deposited on glass carbon electrode (PDHDM/GC), PDHDM/CF exhibited a remarkable specific capacitance of 280 F g −1 at a scan rate of 10 mV s −1 , which was nearly three times that of the PDHDM/GC. The specific capacitance of assembled symmetric supercapacitor based on PDHDM/CF reached 27.35 F g −1 at 0.5 A g −1 and the energy density was 6.38 Wh kg −1 at a power density of 3.9 kW kg −1 . These results indicated that the PDHDM/CF was a promising electrode material for the flexible supercapacitors application. [ABSTRACT FROM AUTHOR]

In this study, a new simple hybrid poly(2-(thiophen-2-yl)furan) (PTFu) was easily electrodeposited by direct anodic oxidation of 2-(thiophen-2-yl)furan in acetonitrile solution containing 0.1 M lithium perchlorate (LiClO 4 ). The oxidation onset potential of 2-(thiophen-2-yl)furan monomer in this medium was measured to be 0.90 V, which was lower than those of thiophene (1.47 V) and furan (1.28 V). The structure and morphology of PTFu were characterized by Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The electrochemical capacitance properties of PTFu electrode in three electrolytes were also investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscope techniques. The electrochemical results showed that the specific capacitance of PTFu electrode was enhanced to 392.0 F g −1 from 249.4 F g −1 at 5 A g −1 and the cycling stability was also enhanced to 67.0% retention from 25.5% retention after 500 cycles when the equivalent boron trifluoride diethyl etherate (BFEE) was added into the acetonitrile electrolyte. Furthermore, the PTFu electrode in ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF 6 ) showed a lower specific capacitance value (209.4 F g −1 at 5 A g −1 ) and an improved stability (67.6% retention after 600 cycles). These results indicated that the conducting polymers based on furan should be a promising electrode material for supercapacitor applications when the electrolyte based-BFEE is used. [ABSTRACT FROM AUTHOR]

Here, three new 3,4-ethylenedioxythiophene bis-substituted bithiophene containing alkyl side chain groups (alkyl = hexyl, octyl, and dodecyl) comonomers, 5,5′-(4,4′-dihexyl-[2,2′-bithiophene]-5,5′-diyl) bis(2,3-dihydrothieno[3,4-b][1,4]dioxine (BEDOT-BT-BH), 5,5′-(4,4′-dioctyl-[2,2′-bithiophene]-5,5′-diyl) bis(2,3-dihydrothieno[3,4-b][1,4]dioxine (BEDOT-BT-BO), and 5,5′-(4,4′-di dodecyl -[2,2′-bithiophene]-5,5′-diyl) bis(2,3-dihydrothieno[3,4-b][1,4]dioxine (BEDOT-BT-BD) were synthesized, and the three comonomers were facilely formed into PBEDOT-BT-BH, PBEDOT-BT-BO, and PBEDOT-BT-BD polymers on platinum electrode by direct anodic oxidation, respectively. The structure and morphology of the polymers were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermal analysis. Electrochemical performances of the polymers were also studied by galvanostatic charge–discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical results showed that three polymers showed good cycle ability and favorable capacitive performance, namely, for PBEDOT-BT-BH, PBEDOT-BT-BO, and PBEDOT-BT-BD, the specific capacitance was 132.5 F/g, 135.4 F/g, and 129.3 F/g (three electrode configurations) at 1 A/g, respectively, the capacitance retention was nearly 50.1%, 84.6% and 77.1% after 1000 cycles. The energy density of the symmetric full cell based on two PBEDOT-BT-BO electrodes was 9.5 Wh/kg −1 at a power density of 13.8 kW/kg −1 . These results implied that the three conducting polymers will be a kind of promising electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen-vacancy WO 3 and WO 3 -CeO 2 nanowires are synthesized by hydrothermal method. • Organic-inorganic hybrid electrode is proposed including PEDOT:PSS, WO 3 -CeO 2 and PEDOT. • WO 3 -CeO 2 -based electrode shows ultrahigh capacitance of 1310 mF cm−2 at 2 mA cm−2. • ASC device shows high energy density and long-term cycling stability comparable to batteries. Although WO 3 with high theoretical capacitance has a future in the field of energy storage, its electrode processing to obtain high capacitance is still a challenge. Here, we propose an innovative electrode structure design by utilizing PEDOT and PEDOT:PSS to sequentially assemble with the oxygen vacancies-enriched WO 3 and WO 3 -CeO 2 hybrid nanowires on the glassy carbon (GC). As-prepared PEDOT:PSS/WO 3 /PEDOT/GC and PEDOT:PSS/WO 3 -CeO 2 /PEDOT/GC electrodes show high areal capacitance of 1139.6 and 1310 mF cm−2 at 2 mA cm−2, respectively, greater than 822.3 mF cm−2 of the WO 3 -PTFE-C/GC. The asymmetric supercapacitor based on PEDOT:PSS/WO 3 -CeO 2 /PEDOT and PEDOT:PSS/RuO 2 /PEDOT electrodes works at 1.6 V high working voltage, delivers an energy density of 0.61 Wh m−2 at power density of 8.22 W m−2. Therefore, the electrode structure design will be suitable to improve the capacitance performance of other low-conductivity active materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel 3,4-ethylenedioxythiophene bis-substituted bithiophene (BEDOT-BT) was synthesized. [•] BEDOT-BT was further electropolymerized into PEDOT-BT polymer. [•] PEDOT-BT had high thermal stability and electrochemical cycling stability. [•] The specific capacitance of PBEDOT-BT electrode reached 171 F g−1 at 1 A g−1. [ABSTRACT FROM AUTHOR]

[Display omitted] • A porous poplar flower-like PEDOT-MeOH/PEG/WS 2 composite was fabricated. • The PEDOT-MeOH/PEG/WS 2 showed a high capacitance of 461.5 mF cm−2 at 5 mV s−1. • The device presented a specific energy of 8.72 × 103 μWh cm−2 at 2.62 × 105 μW cm−2. • The capacitive retention was 83.6% after 5000 charge-discharge cycles. The morphology of electrode material is generally critical to affecting their electrochemical performance. Here, a porous poplar flower-like PEDOT-MeOH/PEG/WS 2 hybrid material is successfully prepared using a simply co-electrodeposition method. With the assistance of poly(ethylene glycol) (PEG), the chemically exfoliated WS 2 nanosheets are doped into poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-MeOH) film. The formation of a porous poplar flower-like PEDOT-MeOH/PEG/WS 2 composite is proved by scanning electron microscopy, transmission electron microscopy, infrared spectra, energy-dispersive X-ray spectrometry and X-ray photoelectron spectroscopy. The maximum capacitance of the composite reaches 461.5 mF cm−2, which is 1.6 times greater than that of PEDOT-MeOH/PEG film. As-fabricated PEDOT-MeOH/PEG/WS 2 composite can keep 85.8% of the initial areal capacitance after 5000 cycles. Additionally, PEDOT-MeOH/PEG/WS 2 -based symmetrical supercapacitor presents a capacitive capacity of 62.7 mF cm−2 at 0.5 mA cm−2, specific energy of 8.72 × 103 μWh cm−2 at 2.62 × 105 μW cm−2, and capacitive retention of 83.3% after 5000 cycles with a 100% coulombic efficiency. The capacitance improvement of PEDOT-MeOH/PEG/WS 2 composite is closely related to porous poplar flower-like structure as well as the cooperation-enhancing effect between PEDOT-MeOH and WS 2. These results imply that PEDOT-MeOH/PEG/WS 2 composite will have great potential application in the field of the energy storage. [ABSTRACT FROM AUTHOR]

• Hierarchical PEDOT@MoS 2 composite was fabricated by electrochemical co-deposition. • As a separate electrode, it exhibits ultra-high capacitance and remarkable cycling stability. • The assembled supercapacitor delivers high energy density and excellent cycling stability. Hierarchical structural PEDOT@MoS 2 nanocomposite is synthesized via a facile electrochemical co-deposition of the intercalation of PEDOT into flower-like MoS 2 microspheres. The SEM, TEM, and other characterization results demonstrate the hierarchical PEDOT@MoS 2 composite with an enlarged interlayer spacing of MoS 2 to 1.02 nm, in which PEDOT nanoparticles act as intercalation, and flower-like MoS 2 microspheres are used as a substrate for growth. The electrochemical characterizations indicate that the PEDOT@MoS 2 electrode has an ultra-high specific capacitance of 4418 mF cm−2 at 2 mA cm−2 and remarkable cycling stability, retaining 100% of the initial capacitance at a high current density of 100 mA cm−2 after 10,000 cycles. The symmetric PEDOT@MoS 2 supercapacitor presents a high energy density of 88.3 mWh cm−2 at 60 mW cm−2, and outstanding cycling stability (93% after 10,000 cycles). These prominent electrochemical performances are attributed to the expanded interlayer spacing, the synergistic effect between PEDOT and MoS 2 , the low resistance, along with the PEDOT@MoS 2 porous structure, indicating great potential applications of the PEDOT@MoS 2 electrode in the energy storage field. [ABSTRACT FROM AUTHOR]

An active material electrode with high areal specific capacitance is needed for a high-performance supercapacitor, but it is difficult to achieve this goal for PEDOT-based composites. Here, a novel hierarchical core/shell PEDOT@MoS 2 composite was assembled by the electrochemical co-deposition of EDOT and MoS 2 submicron spheres. The SEM, TEM images of the as-obtained composite explicitly reveal the core/shell heterostructure of PEDOT@MoS 2 with a diameter of about 800 nm. The electrochemical characterizations show that the optimized PEDOT@MoS 2 composite possesses a high specific capacitance of 2540 mF cm−2 at 1 mA cm−2 and excellent capacitance retention of 98.5% after 5000 cycles at a high current density of 100 mA cm−2. The assembled P@M-4//PEDOT asymmetric supercapacitor shows a high energy density of 937 Wh m −2 at 6500 W m −2, and outstanding cycling stability with capacitance retention of 100% after 5000 cycles. It is proposed that the enhanced performances are attributed to the robust hierarchical core/shell structures and the synergic effect between PEDOT and MoS 2 , which is expected to become a promising candidate for applications in high-performance supercapacitors. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• PEDOT: PSS/rGO fibers are prepared by easily-accessible hydrothermal confinement reaction. • PEDOT:PSS/rGO fiber with simultaneously enhanced capacitance and mechanical properties can be obtained. • The fiber-shaped supercapacitor shows a high specific energy density of 10.68 Wh•kg−1 at the power density of 81.25 W kg−1. Implantable, flexible and easily reconfigurable supercapacitors with high power and energy densities are considered necessary for the development of portable and wearable electronics. However, obtaining a fiber-incorporating high electrochemical performance and fracture elongation remains a huge challenge. Here, we prepare a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)/reduced graphene oxide (PEDOT:PSS/rGO) fiber (PGF) with high-quality electrodes for supercapacitors by easily-accessible hydrothermal confinement reaction. The optimized P 3 G 7 F exhibits improved electrochemical performance including a high specific capacitance (C s) of 249.5 F g −1 at 0.5 A g −1 and good cycling stability. Moreover, after introducing the PEDOT:PSS, the elongation at break of the P 3 G 7 F is doubled to 13.9%. A symmetric supercapacitor (SSC) based on the P 3 G 7 F displays a high specific energy density of 10.68 Wh kg−1 at a specific power density of 81.25 W kg−1. The improved performance of the fabricated composite fiber is attributed to the unique structures of the rGO and PEDOT:PSS and their synergistic effect. This study introduces an opportunity for the development of next-generation flexible and wearable devices. PEDOT:PSS/rGO fibers are prepared via easily-accessible hydrothermal confinement method and the PEDOT:PSS/rGO fibers exhibit good capacitance and mechanical properties. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Few-layered crumpled porous N-doped graphene was prepared using nitroaromatic molecules as N sources. • Nitroaromatic molecules effectively suppressed the aggregation of N-doped graphene. • As-obtained 5-NIGN had high specific capacitance of 457.4 F g−1 and long cycle life. Nitroaromatic pollutants with unusually strong adsorption affinity are highly attractive candidates for creating 2D molecular assemblies on the surface of graphene, which is crucial to prepare high-quality N-doped graphene by post-treatment. Herein, the few-layered crumpled N-doped graphene (5-NIGN) with high N content is successfully prepared by mixing 5-nitroindole (5-NI), ammonia, and graphene oxide (GO) and using a simple hydrothermal method followed by the post-treatment process of vacuum freeze-drying and annealing. It is found that the rapid assembly of 5-NI effectively suppresses the aggregation of the products in the reduction process of GO, so that the thickness of as-prepared 5-NIGN is 4.21 nm, very close to that of GO (4.01 nm). Compared with the N-doped graphene (GN) derived from the system of GO containing ammonia (341 F g−1), 5-NIGN exhibits higher capacitance of 457.4 F g−1 at 1 A g−1 and prominent long-term life (115% of capacitance maintenance upon 10,000 cycles) within the voltage window of 1.0 V. Furthermore, the supercapacitor assembled by 5-NIGN electrodes can deliver the energy density of 15.5 Wh kg−1~18.5 Wh kg−1 at the power density of 8000 W kg−1~800 W kg−1. These results indicate that the 5-NIGN material will have potential advantages in the realm of electrochemical energy storage. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Fluoropolymers have great values in the scientific research and the industrial application, but poor electrochemical properties restricted their use as charge storage materials. In this work, we developed a high-performance poly(5-fluoroindole) (5-PFIn) as charge storage material by simple electrodeposition of 5-fluoroindole in acetonitrile solution containing 0.1 M Bu 4 NBF 4. The morphologies, structures and electrochemical properties of as-prepared 5-PFIn were studied by SEM, FT-IR, UV–vis, BET and electrochemical techniques, respectively. The electrochemical results indicated that the 5-PFIn nanowires in 1.0 M H 2 SO 4 electrolyte showed a full-covered strongly responsive redox behavior between −0.4 V and 0.85 V, which remarkably differed from polyindole (PIn) and poly(5-methoxyindole) (5-PMeOIn) and poly(indole-5-carboxylic acid) (5-PICA). As a result, 5-PFIn exhibited high specific capacitance of 416 F g−1 at 10 A g−1, good cycling stability of 83% after 5000 cycles and slow self-discharge behavior, which were superior to those of PIn (103 F g−1, 68%), 5-PMeOIn (114 F g−1, 70%) and 5-PICA (286 F g−1, 70%). These results indicated that the fluorine-substituted conjugated PIn will be one of the most promising fluoropolymers electrode materials for supercapacitor application. [ABSTRACT FROM AUTHOR]