Surface modulated hierarchical graphene film via sulfur and phosphorus dual-doping for high performance flexible supercapacitors

The steam-assistant heteroatoms of sulfur and phosphorus dual-doped graphene film fabricated via an ice-template and thermal-activation approach demonstrates an excellent pseudocapacitive behavior in flexible electrochemical capacitors.     

Improving the electrochemical performances of active carbon-based supercapacitors through the combination of introducing functional groups and using redox additive electrolyte

High-performance and low-cost electrochemical capacitors (ECs) are essential for large-scale applications in energy storage. In this work, the specific capacitance of active carbon (AC) electrode was significantly improved through the combination of introducing functional groups on the surface of AC and adding redox-active molecules (K₃Fe(CN)₆) into 2?M KOH aqueous electrolytes. The surface-oxygen functionalized AC (FAC) was synthesized using HNO₃ echoed as the electrode and 2?M KOH with 0.1?M K₃Fe(CN)₆ as the electrolyte. The surface functional groups of the AC not only contribute to the pseudocapacitance but also increase the active sites of the electrode/electrolyte interface, which enhances the electrochemical activity of the Fe(CN)₆^3?/Fe(CN)₆^4? redox pair, thus leading to high capacitance. In the redox electrolyte, the specific capacitance was much higher in 229.17?F?g^?1 (1?A?g^?1) achieved for those FAC than in raw AC (only 147.06?F?g^?1). Similarly, the FAC electrode suggested high energy density and extended cycling stability in the KOH?+?K₃Fe(CN)₆ electrolyte.     

Synthesis of few-layer N-doped graphene from expandable graphite with melamine and its application in supercapacitors

In this paper,we introduced a novel method to prepare the few-layer nitrogen-doped graphene(FNG)from expandable graphite with melamine.The super-capacitive properties of FNG were thoroughly characterized by a three-electrode system,and the results showed the FNG electrode achieved a specific capacitance as high as 83.8 mF/cm2 together with excellent cycling stability.This method could be a novel approach to combine the pseudo-capacitors and electric double layer capacitors.     

Temperature stability of symmetric activated carbon supercapacitors assembled with in situ electrodeposited poly(vinyl alcohol) potassium borate hydrogel electrolyte

Temperature stability of symmetric activated carbon (AC) supercapacitors (SCs) assembled with in situ electrodeposited poly(vinyl alcohol) potassium borate hydrogel electrolyte was systematically studied and compared with that of AC SCs assembled with liquid aqueous electrolytes in the temperature range from -5℃ to 80℃.     

Controlling wrinkles and assembly patterns in dried graphene oxide films using lyotropic graphene oxide liquid crystals

We fabricated graphene oxide (GO) films on glass substrates by blade coating a lyotropic GO liquid crystal dispersion. Substrate temperature and blading speed were precisely controlled to manipulate the surface morphologies of GO films. The temperature and blade speed influenced the drying rate of film and the amount GO dispersion supplied. By controlling these parameters, film-thickness modulation and three types of surface wrinkle patterns were selectively achieved. We also plotted the wrinkle patterns diagram as functions of the film fabrication conditions. The films exhibited different optical anisotropies depending on wrinkle patterns. GO films with controlled wrinkles can be used as electrodes for supercapacitor applications owing to the large surface areas.     

Application of a novel redox-active electrolyte in MnO2-based supercapacitors

This paper reports a novel strategy for preparing redox-active electrolyte through introducing a redox-mediator(p-phenylenediamine,PPD) into KOH electrolyte for the application of ball-milled MnO 2-based supercapacitors.The morphology and compositions of ball-milled MnO 2 were characterized using scanning electron microscopy(SEM) and X-ray diffraction(XRD).The electrochemical properties of the supercapacitor were evaluated by cyclic voltammetry(CV),galvanostatic charge-discharge(GCD),and electrochemical impedance spectroscopy(EIS) techniques.The introduction of p-phenylenediamine significantly improves the performance of the supercapacitor.The electrode specific capacitance of the supercapacitor is 325.24 F g-1,increased by 6.25 folds compared with that of the unmodified system(44.87 F g-1) at the same current density,and the energy density has nearly a 10-fold increase,reaching 10.12 Wh Kg-1.In addition,the supercapacitor exhibits good cycle-life stability.     

Promoting operating voltage to 2.3 V by a superconcentrated aqueous electrolyte in carbon-based supercapacitor

Aqueous supercapacitors(SCs) have attracted more and more attention for their safety,fast charge/discharge capability and ultra-long life.However,the application of aqueous SCs is limited by the low working voltage due to the narrow electrochemical stability window(ESW) of wate r.Herein,we report a new water in salt(WIS) electrolyte by dissolving potassium bis(fluorosulfonyl) amide(KFSI) in water with an ultra-high mass molar concentration of 37 mol/kg.The highly concentrated electrolyte can achieve a wide ESW of 2.8 V.The WIS electrolyte enables a safe carbon-based symmetrical supercapacitor to operate stably at 2.3 V with an ultra-long cycle life and excellent rate performance.The energy density reaches 20.5 Wh/kg at 2300 W/kg,and the capacity retention is 83.5% after 50,000 cycles at a current density of 5 A/g.This new electrolyte will be a promising candidate for future high-voltage aqueous supercapacitors.     

The solubility of argon in aqueous solutions of a complex-ion electrolyte

From measurements of the solubility of argon in aqueous solutions of the complexion electrolyte t-[Co(en)₂NCSCl]Br at 25°C, the Setschenow parameter for this system is found to be +0.33₆. Using the scaled-particle theory of the salt effect with this value ofk ₅ and the Waddington crystal radius of the Br^– ion, 1.98 Å, the radius of the complex cation is calculated to be 3.71 Å. This value is in reasonably good agreement with that estimated from scale models of the t-[Co(en)₂-NCSCl]⁺ cation, about 3.9 Å. It is somewhat larger than the radius calculated from various semiempirical equations relating the molal volume of an ion at infinite dilution to its radius; values of r obtained in this manner range from 3.32 to 3.66 Å.Abstracted, in part, from D.P.'s M.S. thesis, June 1971.     

An improved biosensor for acetaldehyde determination using a bienzymatic strategy at poly(neutral red) modified carbon film electrodes

Improved biosensors for acetaldehyde determination have been developed using a bienzymatic strategy, based on a mediator-modified carbon film electrode and co-immobilisation of NADH oxidase and aldehyde dehydrogenase. Modification of the carbon film electrode with poly(neutral red) mediator resulted in a sensitive, low-cost and reliable NADH detector. Immobilisation of the enzymes was performed using encapsulation in a sol-gel matrix or cross-linking with glutaraldehyde. The bienzymatic biosensors were characterized by studying the influence of pH, applied potential and co-factors. The sol-gel and glutaraldehyde biosensors showed a linear response up to 60 μM and 100 μM, respectively, with detection limits of 2.6 μM and 3.3 μM and sensitivities were 1.7 μA mM⁻¹ and 5.6 μA mM⁻¹. The optimised biosensors showed good stability and good selectivity and have been tested for application for the determination of acetaldehyde in natural samples such as wine.     

A simple empirical equation for the prediction of the activity-coefficient value of each component in aqueous electrolyte mixtures containing a common ion

A simple empirical equation is presented for the prediction of the mean ionic activity coefficient of each component in aqueous electrolyte mixtures containing a common ion. The results obtained in a variety of two- and three-electrolyte mixtures show that in most cases log values predicted by this equation are consistent with values predicted using an elaborate ion-component model.     

Simultaneous determination of atropine,scopolamine, and anisodamine in Flos daturae by capillary electrophoresis using a capillary coated by graphene oxide

A novel CE method was developed for the separation and determination of three main tropane alkaloids in Flos daturae with a capillary coated by graphene oxide (GO). The GO‐coated capillary was characterized by SEM, energy dispersive X‐ray spectroscopy, and Raman spectroscopy, and the results indicated that the inner surface of the capillary was partially coated by GO. A phosphate solution (40 mM, pH7.0) containing 20% v/v methanol and 30% v/v acetonitrile was used as the running buffer for the analysis of the atropine, scopolamine, and anisodamine. The linear ranges of atropine, scopolamine, and anisodamine was 0.5–200 μg/mL with satisfactory correlation coefficients (R²) > 0.9987, and this novel method provided an efficient separation for three tropane alkaloids as well as a good reproducibility and stability. Finally, the method was successfully applied for the determination of these three tropane alkaloids in plant extracts.     

Electrospun polystyrene/graphene nanofiber film as a novel adsorbent of thin film microextraction for extraction of aldehydes in human exhaled breath condensates

In the current study, we introduced a novel polystyrene/graphene (PS/G) composite nanofiber film for thin film microextraction (TFME) for the first time. The PS/G nanofiber film was fabricated on the surface of filter paper by a facile electrospinning method. The morphology and extraction performance of the resultant composite film were investigated systematically. The PS/G nanofiber film exhibited porous fibrous structure, large surface area and strong hydrophobicity. A new thin film microextraction-high performance liquid chromatography (TFME-HPLC) method was developed for the determination of six aldehydes in human exhaled breath condensates. The method showed high enrichment efficiency and fast analysis speed. Under the optimal conditions, the linear ranges of the analytes were in the range of 0.02–30 μmol L⁻¹ with correlation coefficients above 0.9938, and the recoveries were between 79.8% and 105.6% with the relative standard deviation values lower than 16.3% (n = 5). The limits of quantification of six aldehydes ranged from 13.8 to 64.6 nmol L⁻¹. The established method was successfully applied for the quantification of aldehyde metabolites in exhaled breath condensates of lung cancer patients and healthy people. Taken together, the TFME-HPLC method provides a simple, rapid, sensitive, cost-effective, non-invasion approach for the analysis of linear aliphatic aldehydes in human exhaled breath condensates.     

Surface plasmon resonance as a probe of interactions between a thin‐film gold electrode and an aqueous supporting electrolyte containing 1‐ethyl‐3‐methyl‐imidazolium ethyl sulfate ionic liquid

Surface plasmon resonance (SPR) and electrochemical measurements are combined in this work to study the interactions of a gold film electrode with aqueous electrolytes of an ionic liquid (IL), 1‐ethyl‐3‐methyl‐imidazolium ethyl sulfate. The optical response of the bulk electrolyte strongly affects the SPR angles, and the critical angle data help to separate these bulk effects from those arising strictly from the electrode surface. The optical parameters of the Au‐electrolyte system are determined by fitting the SPR angle‐spectra to calculated results of a multilayer reflectivity model. Both in the absence and in the presence of externally applied voltages, the SPR signal of the experimental interface is dominated by the dielectric behavior of the bulk electrolyte. No significant chemisorptions are detected for the IL contents (0.036–0.087 mole fraction) of the electrolytes used. The results demonstrate how angle resolved SPR measurements can be employed to determine the suitability of specific ILs as solutes for aqueous background electrolytes in electrochemical SPR sensing experiments. Copyright © 2011 John Wiley & Sons, Ltd.     

Engineered interface using a hydroxyl group‐free polymeric buffer layer onto a TiO2 nanocomposite film for improving the electrical properties in a low‐voltage operated organic transistor

We demonstrate the effect of engineered interfaces by introducing different classes of polymeric buffer layers onto a titanium oxide (TiO₂) nanocomposite film on the density of interfacial trap sites and corresponding mobility in low‐voltage‐operated organic field‐effect transistors. The organic field‐effect transistors were fabricated using pentacene as an organic semiconductor layer and a high dielectric TiO₂ nanocomposite film for low‐voltage operation stacked with two different kinds of thin polymers, one of which is hydroxyl group‐existing polyvinyl phenol and the other is hydroxyl group‐free polyvinyl cinnamate. By using the hydroxyl group‐free buffer layer, the interfacial trap density is found to be much decreased than that for the hydroxyl group‐existing buffer layer. In addition, the mobility for the polyvinyl cinnamate used case, shows significantly increased value by at least one of magnitude compared to the case of no buffer layer. It is found that a hydroxyl group‐free polymeric layer produces a more effective surface, which leads to high electrical properties and less electrochemical traps at the interface in the organic devices. Copyright © 2011 John Wiley & Sons, Ltd.     

Conjugates of polyhedral boron compounds with carbohydrates. 2. Unexpected easy closo- to nido-transformation of a carborane-carbohydrate conjugate in neutral aqueous solution

A novel 1,2-dicarba-closo-dodecaborane-lactose conjugate 4c, when dissolved in water or methanol, is subject to unexpected deboronation in neutral conditions leading to the formation of the corresponding nido-counterpart (5) as detected by ¹¹B NMR spectroscopy. After heating the aqueous solution of the conjugate 4c at 60 °C for 17 h pure 1,2-dicarba-nido-undecaborane-lactose conjugate 5 was obtained.     

Methanol vapor‐induced morphology and current–voltage characteristic changes in a cast‐coated nafion film/interdigitated microarray electrode

Methanol vapor‐induced membranous changes in a cast‐coated Nafion thin film were studied through current–voltage (I–V) characteristics with an interdigitated microarray (IDA) electrode and atomic force microscopy (AFM). The obtained I–V curves showed that the as‐prepared Nafion film was stable under humidified nitrogen gas; however, the I–V profile dramatically changed with exposure to methanol vapor. Next, the morphology of the film was compared before and after methanol exposure with AFM images. On the basis of our observations, we found that the as‐prepared film had an irregularly complicated microstructure, whereas the structure became homogeneous in appearance after 30 min of exposure to methanol gas. The alternating‐current conductivity data, showing almost the same magnitude before and after exposure, strongly suggested that the I–V profile shift was based on a change in an electrode reaction mechanism induced by a change in the junction at the Nafion/IDA electrode interface. Furthermore, the methanol vapor‐pre‐exposed Nafion was stable for further exposure to methanol vapor, water vapor, or both. With the stabilized film used in combination with the IDA electrode, a reversible change in the magnitude of the current was observed when the methanol/water vapor ratio was varied. This indicated that the electrode reaction had good reproducibility after the treatment. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1103–1109, 2002     

A mild, highly selective and remarkably easy procedure for deprotection of aromatic acetates using ammonium acetate as a neutral catalyst in aqueous medium

Ammonium acetate was found to catalyze efficiently the selective deprotection of aromatic acetates in the presence of various sensitive functionalities in aqueous methanol under neutral conditions at room temperature to yield the corresponding phenols in excellent yields. The method has been utilized for deprotection of acetates of several naturally occurring bioactive phenolic compounds and for preparation of venkatasin, a natural coumarino-lignan, from the anticancer compound cleomiscosin A.     

Simultaneous assay of glucose,lactate, <Emphasis Type="SmallCaps">L</Emphasis>-glutamate and hypoxanthine levels in a rat striatum using enzyme electrodes based on neutral red-doped silica nanoparticles

An electrochemical method suitable for the simultaneous measurement of cerebral glucose, lactate, L-glutamate and hypoxanthine concentrations from in vivo microdialysis sampling has been successfully performed for the first time using a neutral red-doped silica (NRDS) nanoparticle-derived enzyme sensor system. These uniform NRDS nanoparticles (about 50±3 nm) were prepared by a water-in-oil (W/O) microemulsion method, and characterized by a TEM technique. The neutral red-doped interior maintained its high electron-activity, while the exterior nano-silica surface prevented the mediator from leaching out into the aqueous solution, and showed high biocompability. These nanoparticles were then mixing with the glucose oxidase (GOD), lactate oxidase (LOD), L-glutamate oxidase (L-GLOD) or xanthine oxidase (XOD), and immobilized on four glassy carbon electrodes, respectively. A thin Nafion film was coated on the enzyme layer to prevent interference from molecules such as ascorbic acid and uric acid in the dialysate. The high sensitivity of the NRDS modified enzyme electrode system enables the simultaneous monitoring of trace levels of glucose, L-glutamate, lactate and hypoxanthine in diluted dialysate samples from a rat striatum.     

Stripping chronopotentiometric measurements of lead(II) and cadmium(II) in soils extracts and wastewaters using a bismuth film screen-printed electrode assembly

The key to remediative processes is the ability to measure toxic contaminants on-site using simple and cheap sensing devices, which are field-portable and can facilitate more rapid decision-making. A three-electrode configuration system has been fabricated using low-cost screen-printing (thick-film) technology and this coupled with a portable electrochemical instrument has provided a a relatively inexpensive on-site detector for trace levels of toxic metals. The carbon surface of the screen-printed working electrode is used as a substrate for in situ deposition of a metallic film of bismuth, which allows the electrochemical preconcentration of metal ions. Lead and cadmium were simultaneously detected using stripping chronopotentiometry at the bismuth film electrode. Detection limits of 8 and 10 ppb were obtained for cadmium(II) and lead(II), respectively, for a deposition time of 120 s. The developed method was applied to the determination of lead and cadmium in soils extracts and wastewaters obtained from polluted sites. For comparison purposes, a mercury film electrode and ICP-MS were also used for validation.     

Preparation of COF2 using CO2 and F2 in the electrochemical cell with PbSnF4 as a solid electrolyte

Tetragonal PbSnF₄ was prepared by precipitation method with Pb(NO₃)₂ and SnF₂ aqueous solutions. The product was characterized using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XFS), and the other chemical analyses. Tetragonal PbSnF₄ exhibited the highest electric conductivity of 3.2 Sm⁻¹ at 473 K in air as a fluoride ion conductor. We have investigated the possibility of COF₂ formation using CO₂ and F₂ in an electrochemical cell with PbSnF₄ as a solid electrolyte. At same time, we tried to produce an electric power from an electrochemical cell. This CO₂/F₂ electrochemical cell was constructed with a tetragonal PbSnF₄ disk having Au electrodes. The electromotive force was about 0.9 V at room temperature for 0.1 MPa CO₂/(0.01 MPa F₂ + 0.09 MPa Ar). However, the short circuit current density was 0.24 A m⁻², which was quite small. This current density was so small that no fluorocarbon compound was detected after 3 h discharge using FT-IR.