High‐Performance,Stretchable, Wire‐Shaped Supercapacitors

A general approach toward extremely stretchable and highly conductive electrodes was developed. The method involves wrapping a continuous carbon nanotube (CNT) thin film around pre‐stretched elastic wires, from which high‐performance, stretchable wire‐shaped supercapacitors were fabricated. The supercapacitors were made by twisting two such CNT‐wrapped elastic wires, pre‐coated with poly(vinyl alcohol)/H₃PO₄ hydrogel, as the electrolyte and separator. The resultant wire‐shaped supercapacitors exhibited an extremely high elasticity of up to 350 % strain with a high device capacitance up to 30.7 F g⁻¹, which is two times that of the state‐of‐the‐art stretchable supercapacitor under only 100 % strain. The wire‐shaped structure facilitated the integration of multiple supercapacitors into a single wire device to meet specific energy and power needs for various potential applications. These supercapacitors can be repeatedly stretched from 0 to 200 % strain for hundreds of cycles with no change in performance, thus outperforming all the reported state‐of‐the‐art stretchable electronics.     

High‐Performance,Stretchable, Wire‐Shaped Supercapacitors

A general approach toward extremely stretchable and highly conductive electrodes was developed. The method involves wrapping a continuous carbon nanotube (CNT) thin film around pre‐stretched elastic wires, from which high‐performance, stretchable wire‐shaped supercapacitors were fabricated. The supercapacitors were made by twisting two such CNT‐wrapped elastic wires, pre‐coated with poly(vinyl alcohol)/H₃PO₄ hydrogel, as the electrolyte and separator. The resultant wire‐shaped supercapacitors exhibited an extremely high elasticity of up to 350 % strain with a high device capacitance up to 30.7 F g^?1, which is two times that of the state‐of‐the‐art stretchable supercapacitor under only 100 % strain. The wire‐shaped structure facilitated the integration of multiple supercapacitors into a single wire device to meet specific energy and power needs for various potential applications. These supercapacitors can be repeatedly stretched from 0 to 200 % strain for hundreds of cycles with no change in performance, thus outperforming all the reported state‐of‐the‐art stretchable electronics.     

Indirect Transformation of Coordination‐Polymer Particles into Magnetic Carbon‐Coated Mn3O4 (Mn3O4@C) Nanowires for Supercapacitor Electrodes with Good Cycling Performance

Carbon‐coated Mn₃O₄ nanowires (Mn₃O₄@C NWs) have been synthesized by the reduction of well‐shaped carbon‐coated bixbyite networks and characterized by TEM, X‐ray diffraction, X‐ray photoelectron spectroscopy, and electrochemical experiments. To assess the properties of 1D carbon‐coated nanowires for their use in supercapacitors, cyclic voltammetry and galvanostatic charging–discharging measurements were performed. Mn₃O₄@C NWs could be charged and discharged faster and had higher capacitance than bare Mn₃O₄ nanostructures and other commercial materials. The capacitance of the Mn₃O₄@C NWs was 92 % retained after 3000 cycles at a charging rate of 5 A g^?1. This improvement can be attributed to the carbon shells, which promote fast Faradaic charging and discharging of the interior Mn₃O₄ core and also act as barriers to protect the inner core. These Mn₃O₄@C NWs could be a promising candidate material for high‐capacity, low‐cost, and environmentally friendly electrodes for supercapacitors. In addition, the magnetic properties of the as‐synthesized samples are also reported to investigate the influence of the carbon coating.     

Constructing Hierarchical Tectorum‐like α‐Fe2O3/PPy Nanoarrays on Carbon Cloth for Solid‐State Asymmetric Supercapacitors

The design of complex heterostructured electrode materials that deliver superior electrochemical performances to their individual counterparts has stimulated intensive research on configuring supercapacitors with high energy and power densities. Herein we fabricate hierarchical tectorum‐like α‐Fe₂O₃/polypyrrole (PPy) nanoarrays (T‐Fe₂O₃/PPy NAs). The 3D, and interconnected T‐Fe₂O₃/PPy NAs are successfully grown on conductive carbon cloth through an easy self‐sacrificing template and in situ vapor‐phase polymerization route under mild conditions. The electrode made of the T‐Fe₂O₃/PPy NAs exhibits a high areal capacitance of 382.4 mF cm⁻² at a current density of 0.5 mA cm⁻² and excellent reversibility. The solid‐state asymmetric supercapacitor consisting of T‐Fe₂O₃/PPy NAs and MnO₂ electrodes achieves a high energy density of 0.22 mWh cm⁻³ at a power density of 165.6 mW cm⁻³.     

Enhanced power production of microbial fuel cells by reducing the oxygen and nitrogen functional groups of carbon cloth anode

The physicochemical properties of anode material are important for the electron transfer of anode bacteria and electricity generation of microbial fuel cells (MFCs). In this work, carbon cloth anode was pretreated with isopropanol, hydrogen peroxide (H₂O₂) and sodium hypochlorite (NaOCl) in order to reduce the anode functional groups. The influence of functional groups on the electrochemical properties of carbon cloth anode and power generation of MFCs was investigated. The anode pretreatments removed the surface sizing layer of carbon cloth and substantially reduced the contents of C‐O and pyridinic/pyrrolic N groups on the anode. Electrochemical impedance spectroscopy and cyclic voltammetry analyses of the biofilm‐matured anodes revealed an enhanced electrochemical electron transfer property because of the anode pretreatments. As compared with the untreated control (612 ± 6 mW m^?2), the maximum power density of an acetate‐fed single‐chamber MFC was increased by 26% (773 ± 5 mW m^?2) with the isopropanol treated anode. Additional treatment with H₂O₂ and NaOCl further increased the maximum power output to 844 ± 5 mW m^?2 and 831 ± 4 mWm^?2. A nearly inverse liner relationship was observed between the contents of C‐O and pyridinic/pyrrolic N groups on anodes and the anodic exchange current density and the power output of MFCs, indicating an adverse effect of these functional groups on the electricity production of anodes. Results from this study will further our understanding on the microbial interaction with carbon‐based electrodes and provide an important guidance for the modification of anode materials for MFCs in future studies. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrochemical Capacitors

The current literature sources on the electrochemical capacitors, which are divided into the film (dielectric), electrolytic, and supercapacitors, are reviewed. The supercapacitors are in turn subdivided into the double-layer capacitors, which use the EDL recharge on a highly-developed interfacial surface of electrodes; pseudocapacitors, where the charge is stored in a faradaic pseudocapacitance of sufficiently reversible redox reactions and the EDL capacitance; and hybrid capacitors, which employ a variety of electrodes. A macrokinetic theory of operation of double-layer capacitors is considered. Effect of various factors on the properties of electrodes utilized in supercapacitors is analyzed. A novel type of hybrid capacitor, which has a negative electrode of activated carbon cloth and a PbSO₄/PbO₂ positive electrode, is proposed. A theory of capillary equilibrium in hermetically sealed electrochemical capacitors is considered. Specific features of the application of voltammetric and impedance methods to studying electrochemical processes in supercapacitors are revealed. Characteristics of electrochemical capacitors and batteries are compared.     

Free‐Standing Conducting Polymer Films for High‐Performance Energy Devices

Thick, uniform, easily processed, highly conductive polymer films are desirable as electrodes for solar cells as well as polymer capacitors. Here, a novel scalable strategy is developed to prepare highly conductive thick poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (HCT‐PEDOT:PSS) films with layered structure that display a conductivity of 1400 S cm^?1 and a low sheet resistance of 0.59 ohm sq^?1. Organic solar cells with laminated HCT‐PEDOT:PSS exhibit a performance comparable to the reference devices with vacuum‐deposited Ag top electrodes. More importantly, the HCT‐PEDOT:PSS film delivers a specific capacitance of 120 F g^?1 at a current density of 0.4 A g^?1. All‐solid‐state flexible symmetric supercapacitors with the HCT‐PEDOT:PSS films display a high volumetric energy density of 6.80 mWh cm^?3 at a power density of 100 mW cm^?3 and 3.15 mWh cm^?3 at a very high power density of 16160 mW cm^?3 that outperforms previous reported solid‐state supercapacitors based on PEDOT materials.     

Dual‐Doped Molybdenum Trioxide Nanowires: A Bifunctional Anode for Fiber‐Shaped Asymmetric Supercapacitors and Microbial Fuel Cells

A novel in situ N and low‐valence‐state Mo dual doping strategy was employed to significantly improve the conductivity, active‐site accessibility, and electrochemical stability of MoO₃, drastically boosting its electrochemical properties. Consequently, our optimized N‐MoO_3?x nanowires exhibited exceptional performances as a bifunctional anode material for both fiber‐shaped asymmetric supercapacitors (ASCs) and microbial fuel cells (MFCs). The flexible fiber‐shaped ASC and MFC device based on the N‐MoO_3?x anode could deliver an unprecedentedly high energy density of 2.29 mWh cm^?3 and a remarkable power density of 0.76 μW cm^?1, respectively. Such a bifunctional fiber‐shaped N‐MoO_3?x electrode opens the way to integrate the electricity generation and storage for self‐powered sources.     

An improvement on the adhesion‐strength of laminated ultra‐high‐molecular‐weight polyethylene fabrics: surface‐etching/modification using highly effective helium/oxygen/nitrogen plasma treatment

In this study, helium/oxygen/nitrogen (He/O₂/N₂)‐plasma was used to etch/modify the surface of ultra‐high‐molecular‐weight polyethylene (UHMWPE) fiber. After coated with polyurethane (PU), the plasma treated UHMWPE fabrics were laminated. It was found that the values of peeling strength between the laminated UHMWPE fabrics treated with He/O₂/N₂‐plasma were significantly higher (3–4 times) than that between pristine fabrics. The hydrophilic property and the value of the surface roughness of the UHMWPE fibers increased significantly after treated with He/O₂/N₂‐plasma. The mechanism of the oxidation/degradation of the polymers on the surface of the UHMWPE fiber during He/O₂/N₂‐plasma treatment was suggested. In addition, it was found that the higher content of functional groups (carbonyl, aldehyde, and carboxylic acid) on fiber surface and the higher value of surface roughness of the UHMWPE fiber treated with He/O₂/N₂‐plasma could significantly improve the adhesion‐strength of the laminated UHMWPE fabric. Especially, the micro‐aperture on the surface of UHMWPE fiber caused by the strenuous etching of He/O₂/N₂‐plasma treatment was also an important factor on improving the adhesion‐strength between the laminated UHMWPE fabrics. Copyright © 2010 John Wiley & Sons, Ltd.     

Enhancing the Kinetic Process in Biphasic Crystalline NiWO4/Amorphous Co-B Electrode Materials toward Energy Storage with Ultrahigh Rate Performance

Here, we report a two-phase crystalline NiWO₄/amorphous Co−B nanocomposite as an electrode material for supercapacitors, which is effectively synthesized via a simple hydrothermal method and chemical precipitation method. The obtained NiWO₄/Co−B exhibits crystal-amorphous contact, which makes it have more active sites than other crystalline-crystalline phase boundaries, thereby enhancing electron transport. The NiWO₄/Co−B electrode with the best mass ratio of crystalline and amorphous exhibits a great specific capacitance and excellent cycle durability. Compared to individual Co−B and NiWO₄, it also shows enhanced rate capability Besides, NiWO₄/Co−B/activated carbon supercapacitor device can provide a good specific capacitance and a maximum energy density of 10.92 Wh kg⁻¹ at 200 W kg⁻¹. This work provides new insights to develop novel electrode materials for energy storage and conversion.     

A microfluidic glucose sensor incorporating a novel thread‐based electrode system

An electrochemical sensor for the detection of glucose using thread‐based electrodes and fabric is described. This device is relatively simple to fabricate and can be used for multiple readings after washing with ethanol. The fabrication of the chip consisted of two steps. First, three thread‐based electrodes (reference, working, and counter) were fabricated by painting pieces of nylon thread with either layered silver ink and carbon ink or silver/silver chloride ink. The threads were then woven into a fabric chip with a beeswax barrier molded around the edges in order to prevent leaks from the tested solutions. A thread‐based working electrode consisting of one layer of silver underneath two layers of carbon was selected to fabricate the final sensor system. Using the chip, a PBS solution containing glucose oxidase (GOx) (10 mg/mL), potassium ferricyanide (K₃[Fe(CN)₆]) (10 mg/mL) as mediator, and different concentrations of glucose (0‐25 mM), was measured by cyclic voltammetry (CV). It was found that the current output from the oxidation of glucose was proportional to the glucose concentrations. This thread‐based electrode system is a viable sensor platform for detecting glucose in the physiological range.     

Silver‐Doped TiO2‐Coated Cotton Fabric as an Effective Photocatalytic System for Dye Decolorization in UV and Visible Light

In this study, titanium tetra‐isopropoxide was used as a precursor of TiO₂ for in situ coating on cotton fabric by sol–gel method. Subsequently, silver nitrate was used as doping agent to prepare silver‐doped TiO₂‐coated cotton fabric during hydrothermal treatment. The treated samples were characterized through field‐emission scanning electron microscopy, energy‐dispersive X‐ray analysis, inductively coupled plasma‐mass spectroscopy and UV–visible absorption spectroscopy to study morphology, composition of deposited elements and light absorption behavior of treated samples. X‐ray photoelectron spectroscopy was carried out to analyze the electronic state of silver in TiO₂‐coated fabric after hydrothermal treatment. Doping of silver on TiO₂‐coated fabric and subsequent hydrothermal treatment was found to enhance dye decolorization rate of rhodamine B dye solution in both UV and visible light radiations with respect to undoped TiO₂. The study shows that an optimal level of silver‐doped TiO₂‐coated fabric can be used repeatedly for dye decolorization without significant loss in its photocatalytic activity. The self‐cleaning properties of samples were also studied using methylene blue as a staining agent. It was observed that the presence of 1.8% silver on the weight of titanium in doped samples provides almost 82% of stain degradation.     

Mesoporous Nickel Oxide Nanowires: Hydrothermal Synthesis,Characterisation and Applications for Lithium‐Ion Batteries and Supercapacitors with Superior Performance

Mesoporous nickel oxide nanowires were synthesized by a hydrothermal reaction and subsequent annealing at 400 °C. The porous one‐dimensional nanostructures were analysed by field‐emission SEM, high‐resolution TEM and N₂ adsorption/desorption isotherm measurements. When applied as the anode material in lithium‐ion batteries, the as‐prepared mesoporous nickel oxide nanowires demonstrated outstanding electrochemical performance with high lithium storage capacity, satisfactory cyclability and an excellent rate capacity. They also exhibited a high specific capacitance of 348 F g^?1 as electrodes in supercapacitors.     

Sodium‐Doped Mesoporous Ni2P2O7 Hexagonal Tablets for High‐Performance Flexible All‐Solid‐State Hybrid Supercapacitors

A simple hydrothermal method has been developed to prepare hexagonal tablet precursors, which are then transformed into porous sodium‐doped Ni₂P₂O₇ hexagonal tablets by a simple calcination method. The obtained samples were evaluated as electrode materials for supercapacitors. Electrochemical measurements show that the electrode based on the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets exhibits a specific capacitance of 557.7 F g^?1 at a current density of 1.2 A g^?1. Furthermore, the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets were successfully used to construct flexible solid‐state hybrid supercapacitors. The device is highly flexible and achieves a maximum energy density of 23.4 Wh kg^?1 and a good cycling stability after 5000 cycles, which confirms that the porous sodium‐doped Ni₂P₂O₇ hexagonal tablets are promising active materials for flexible supercapacitors.     

A Microwave Synthesis of Mesoporous NiCo2O4 Nanosheets as Electrode Materials for Lithium‐Ion Batteries and Supercapacitors

A facile microwave method was employed to synthesize NiCo₂O₄ nanosheets as electrode materials for lithium‐ion batteries and supercapacitors. The structure and morphology of the materials were characterized by X‐ray diffraction, field‐emission scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller methods. Owing to the porous nanosheet structure, the NiCo₂O₄ electrodes exhibited a high reversible capacity of 891 mA h g^?1 at a current density of 100 mA g^?1, good rate capability and stable cycling performance. When used as electrode materials for supercapacitors, NiCo₂O₄ nanosheets demonstrated a specific capacitance of 400 F g^?1 at a current density of 20 A g^?1 and superior cycling stability over 5000 cycles. The excellent electrochemical performance could be ascribed to the thin porous structure of the nanosheets, which provides a high specific surface area to increase the electrode–electrolyte contact area and facilitate rapid ion transport.     

Electrical bistability of organic devices with a polymeric thin film for nonvolatile data storage

In this study, organic memory devices with a single active layer between the two external electrodes were fabricated using an electron‐donor type conjugated polymer and an electron‐acceptor type small organic molecule. The active layer of the memory device was prepared by blending polystyrene, poly[10‐(2′‐ethylhexyl)phenothiazine‐3,7‐diyl], and tetracyanoquinodimethane in 1,2‐dichlorobenzene. The device initially showed a low‐conductance state (OFF state) in the low‐voltage range, and an abrupt current increase, corresponding to the transition to a high‐conductance state (ON state), occurred at a certain voltage (V_th). The ON state could be reverted to the OFF state by applying a voltage higher than V_th. The current ratio between the two states was about 10³ (up to 10⁵). After this transition, the device remained in the ON state even after the applied voltage was removed, and this indicated the nonvolatile characteristics of the device. There was no sharp current degradation in the OFF or ON states for 4500 s of continuous bias. The device‐to‐device performance fluctuation was measured, and the conduction mechanisms in the ON and OFF states were examined by fitting the data to well‐known theoretical models. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A Biofuel Cell Based on Biocatalytic Reactions of Glucose on Both Anode and Cathode Electrodes

Biofuel cells based on electrocatalytic oxidation of NADH and reduction of H₂O₂ have been prepared using carbon fiber electrodes functionalized with graphene nano‐flakes. The electrochemical oxidation of NADH was catalyzed by Meldola's blue (MB), while the reduction of H₂O₂ was catalyzed by hemin, both catalysts were adsorbed on the graphene flakes due to their π‐π staking. In the next set of experiments, the MB‐ and hemin‐electrodes were additionally modified with glucose dehydrogenase (GDH) and glucose oxidase (GOx), respectively. The enzyme catalyzed reactions in the presence of glucose, NAD⁺ and O₂ resulted in the production of NADH and H₂O₂ in situ. The produced NADH and H₂O₂ were oxidized and reduced, respectively, at the bioelectrocatalytic electrodes, thus producing voltage and current generated by the biofuel cell. The enzyme‐based biofuel cells operated in a human serum solution modelling an implantable device powered from the natural biofluid. Finally, two enzyme‐based biofuel cell connected in series and operating in the serum solution produced electrical power sufficient for activation of an electronic watch used as an example device.     

Application of Rhamnolipids as Dispersing Agents for the Fabrication of Composite MnO2-Carbon Nanotube Electrodes for Supercapacitors

The high theoretical capacitance of MnO₂ renders it a promising material for the cathodes of asymmetric supercapacitors. The good dispersion of MnO₂ and conductive additives in a nanocomposite electrode is a key factor for efficient electrode performance. This article describes, for the first time, the application of rhamnolipids (RL) as efficient natural biosurfactants for the fabrication of nanocomposite MnO₂-carbon nanotube electrodes for supercapacitors. RL act as co-dispersants for MnO₂ and carbon nanotubes and facilitate their efficient mixing, which allows for advanced capacitive properties at an active mass of 40 mg cm⁻² in Na₂SO₄ electrolytes. The highest capacitance obtained from the cyclic voltammetry data at a scan rate of 2 mV s⁻¹ is 8.10 F cm⁻² (202.6 F g⁻¹). The highest capacitance obtained from the galvanostatic charge–discharge data at a current density of 3 mA cm⁻² is 8.65 F cm⁻² (216.16 F g⁻¹). The obtained capacitances are higher than the capacitances of MnO₂-based electrodes of the same active mass reported in the literature. The approach developed in this investigation is simple compared to other techniques used for the fabrication of electrodes with high active mass. It offers advantages of using a biocompatible RL biosurfactant.     

Effect of Poly(amine)s on the Redox Properties of Carboxymethylcellulose and Ferrocene‐modified Poly(amine) Layer‐by‐Layer Films

Multilayer films consisting of carboxymethylcellulose (CMC) and ferrocene‐modified poly(ethyleneimine) (Fc‐PEI) or poly(allylamine hydrochloride) (Fc‐PAH) were successfully prepared on a gold electrode to examine their redox properties. The redox current of (Fc‐PEI/CMC)_n film‐coated electrodes increased with the number of layers, while the (Fc‐PAH/CMC)_n film‐coated electrodes exhibited increased response only for the first eight bilayers. The (Fc‐PEI/CMC)_n and (Fc‐PAH/CMC)_n films deposited on the surface of Fc‐free multilayer film‐coated electrodes also showed a redox response. The (PEI/CMC)₅ film‐coated electrode showed redox responses in Fc‐PEI and Fc‐PAH solutions, confirming the uptake of the Fc‐polymers in the inner film. In contrast, the uptake of the Fc‐polymers in the (PAH/CMC)₅ film was severely suppressed, suggesting that different permeability of (PEI/CMC)₅ and (PAH/CMC)₅ films.     

Electrochemical Evaluation of Titanium (IV) Oxide/Polyacrylonitrile Electrospun Discharged Battery Coals as Supercapacitor Electrodes

The TiO₂ nanoparticles are electrospun with polyacrylonitrile (PAN) polymer solution onto the discharged battery coal (DBC) electrode and the results are evaluated as a supercapacitor. The morphology and chemical composition of the synthesized TiO₂ nanoparticles and PAN+TiO₂ nanocomposite fibers were characterized by Scanning electron microscopy, thermogravimetry and FTIR analysis. Supercapacitor measurements and electrochemical characterizations of the electrodes examined by cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical measurements showed that the best current value was obtained from PAN and TiO₂ coated DBC. The performances of both PAN and PAN+TiO₂ coated DBC electrodes were investigated as supercapacitors. PAN+TiO₂/DBC showed the best specific capacitance value of 156.00 F g⁻¹ and PAN/DBC showed 74.93 F g⁻¹. In addition, PAN+TiO₂/DBC exhibited reliable stability performance over 2000.00 cycles.