Fast Electrochemical Response Research Articles

Poly(3, 4-Ethylenedioxythiophene) as Promising Energy Storage Materials in Zinc-Ion Batteries.

Benefiting from the advantages of high conductivity and good electrochemical stability, the conjugated conducting polymer poly (3, 4-ethylenedioxythiophene) is a promising energy storage material in zinc-ion batteries. Zinc-ion batteries have the advantages of high safety, environmental friendliness, and low cost, but suffer from unstable cathode material structure, poor electrical conductivity, and uncontrollable dendritic growth of zinc anodes. PEDOT, with its fast electrochemical response and wide potential window, is expected to make up for the shortcomings and enhance capacity and cycle life of zinc-ion batteries. Herein, in this review different polymerization methods of poly (3, 4-ethylenedioxythiophene) as well as their structure and properties are summarized; the progress in doping strategies related to the increasing conductivity and dispersivity of poly (3, 4-ethylenedioxythiophene) materials is discussed; specific applications of poly (3, 4-ethylenedioxythiophene)-based materials in anode, cathode, electrolyte, and binder of zinc-ion batteries are explored; and the representative advancements for improving the electrochemical performance of poly (3, 4-ethylenedioxythiophene) in zinc-ion batteries are emphasized. Finally, the current challenges of poly (3, 4-ethylenedioxythiophene) as promising materials in zinc-ion batteries and an insight into their future research directions are pointed out.

Fast electrochemical response of PEDOT:PSS electrodes through large combined increases to ionic and electronic conductivities

Conducting polymers serve as the active materials in flexible electrochromic displays, organic electrochemical transistors, supercapacitors, artificial muscle and other electrochemical devices. poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is often employed in these devices since it is widely available, suitable for spraying, printing or casting, and can be treated to obtain high electronic conductivity. However, the ionic resistance limits charging rate and switching speed in this high volumetric capacitance polymer. Here we show that treatments that increase electronic conductivity can also increase ionic conductivity – by a factor of 300. Symmetric PEDOT:PSS supercapacitors with electrode thicknesses of 4.7 µm charge 40 times faster due to the combination of improved ionic and electronic conductivity. In these devices, PEDOT:PSS was deposited on two sides of a porous polymer separator by spray coating, and then soaked in either methanol, methanol mixed with the ionic liquid EMITFSI (50%v/v), ethylene glycol, ethylene glycol mixed with EMITFSI (50%v/v), or dimethyl sulfoxide. Ionic resistance dictates the charging time in untreated films. Treatment with methanol combined with EMITFSI results in the highest ionic conductivity (0.02 S/m), combined with an electronic conductivity of 498 S/m and the highest cut-off frequency. In addition, these treatments increase volumetric capacitance. The increases are most likely due to the removal of insulating PSS by the polar solvents, resulting in the formation of an open polymer structure in which ions can move more freely. Improving the charge/discharge speed has implications on the response times of color displays, energy storage devices, neural recording devices and actuators.

Recent progress in the all‐solid‐state flexible supercapacitors

AbstractIn the past few years, supercapacitors (SCs) have attracted great attention in both academic and industrial sectors due to their high energy storage efficiency, reliable stability, and eco‐friendly process. Flexible solid‐state SCs as one of the ongoing focuses for the development of wearable and portable electronics have become the most promising energy storage devices for the smart power system due to their high power density, fast electrochemical response, high efficiency on the charge‐discharge process, and excellent electrochemical stability. In this study, the recent progress in the electrodes and electrolytes used for approaching high‐performance of the all‐solid‐state flexible SCs is reviewed. We first introduce basic operational principles of various SCs. And then we overview the electrode materials including carbon materials, conducting polymers, transition metal oxides/chalcogenides/nitrides, MXenes, metal‐organic frameworks, covalent‐organic frameworks, and the polymer‐based solid‐state electrolytes in different systems. Afterward, we summarize recent progress in the development of the all‐solid‐state flexible SCs and outlook for future research directions.

Nanotheranostic Interface Based on Antibiotic-Loaded Conducting Polymer Nanoparticles for Real-Time Monitoring of Bacterial Growth Inhibition.

Conducting polymers have been increasingly used as biologically interfacing electrodes for biomedical applications due to their excellent and fast electrochemical response, reversible doping-dedoping characteristics, high stability, easy processability, and biocompatibility. These advantageous properties can be used for the rapid detection and eradication of infections associated to bacterial growth since these are a tremendous burden for individual patients as well as the global healthcare system. Herein, a smart nanotheranostic electroresponsive platform, which consists of chloramphenicol (CAM)-loaded in poly(3,4-ethylendioxythiophene) nanoparticles (PEDOT/CAM NPs) for concurrent release of the antibiotic and real-time monitoring of bacterial growth is presented. PEDOT/CAM NPs, with an antibiotic loading content of 11.9± 1.3% w/w, are proved to inhibit the growth of Escherichia coli and Streptococcus sanguinis due to the antibiotic release by cyclic voltammetry. Furthermore, in situ monitoring of bacterial activity is achieved through the electrochemical detection of β-nicotinamide adenine dinucleotide, a redox active specie produced by the microbial metabolism that diffuse to the extracellular medium. According to these results, the proposed nanotheranostic platform has great potential for real-time monitoring of the response of bacteria to the released antibiotic, contributing to the evolution of the personalized medicine.

Horseradish Peroxidase-Immobilized Graphene Oxide-Chitosan Gold Nanocomposites as Highly Sensitive Electrochemical Biosensor for Detection of Hydrogen Peroxide

The generation of fast electrochemical response with high sensitivity is a significant parameter for enzymatic biosensors. However, establishing nanocomposite based modified electrode with fast electron shuttling between enzymes and the electrode surface for determination of hydrogen peroxide (H2O2) is highly challenging. Herein, the present work aims to develop second generation horseradish peroxidase (HRP) biosensors using Au nanochains dropcasted over electrochemically reduced graphene oxide-chitosan (ERGO-CHIT), a bio-nanocomposite film modified glassy carbon electrode (GCE) for reduction of H2O2 is demonstrated. The experimental conditions including effect of pH, loading of enzyme on the electrode surface and concentration of redox mediator as electrolyte were optimized. As a result, the HRP/Au/ERGO-CHIT/GCE electrode shows a larger enhancement in cathodic current signal with sharp peak response for reduction of H2O2, which can be attributed to the presence of Au nanochains on the modified electrode which improves the electron transfer between heme (Fe2+/Fe3+) center of enzymes on the electrode and the redox mediator in the electrolyte solution. The presence of HQ redox mediator in the electrolyte solution have provided stable peak response and offered more beneficiary in lowering the operating potential for the detection of H2O2 (−0.1 V), thereby reducing the influence from interference species. From the amperometric measurements, the HRP/Au/ERGO-CHIT/GCE modified electrode revealed high sensitivity (368.01 μA mM−1 cm−2) and possesses wide linear range (0.01 to 6.31 mM) which is mainly due to the high surface area and conductivity offered by Au nanochains which are located between ERGO and HRP. The resultant HRP/Au/ERGO-CHIT/GCE was found to possess good operational stability, high reproducibility, repeatability with low detection limits (4 μM), and thus it could be applicable for sensitive and rapid responsive detection of H2O2 in biological, clinical and environmental samples.

Carbon intermediate boosted Fe–ZIF derived α–Fe2O3 as a high-performance negative electrode for supercapacitors

Earth-abundant Fe2O3 is a promising material for the negative electrode of supercapacitors by virtue of its wide potential windows. However, the unsatisfactory electrical conductivity and poor ionic diffusion rate within Fe2O3 results in degraded electrochemical performance. In this work, to address these issues, we demonstrate an easy method to synthesize Fe-based zeolitic imidazolate framework (Fe–ZIF) derived α–Fe2O3@C with remarkable supercapacitive properties. The as-obtained α–Fe2O3@C electrode, with the particular benefit of dispersed distribution of carbon, enabling fast electrochemical response, presents a prospective specific capacitance of 161 Fg−1 at a current density of 1 Ag−1. Furthermore, by using the α–Fe2O3@C architecture as the negative electrode, we fabricated a supercapacitor with Na0.5MnO2 as the positive electrode. Our supercapacitor shows a high energy density of 25 Whkg−1, while the corresponding power density is 2400 Wkg−1 at a current density of 2 Ag−1.

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

AbstractA new electrochemical sensor based on Fe3O4@SiO2‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe3O4@SiO2‐PANI‐Au GCE). The Fe3O4@SiO2‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe3O4@SiO2‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10−8 to 1.5×10−5 mol L−1, and the limit of detection was 3.8×10−9 mol L−1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.

Self-Assembled Monolayers of Redox-Active 4d-4f Heterobimetallic Complexes.

In this work, we report the preparation of functional interfaces incorporating heterobimetallic systems consisting in the association of an electroactive carbon-rich ruthenium organometallic unit and a luminescent lanthanide ion (Ln = Eu3+ and Yb3+). The organometallic systems are functionalized with a terminal hexylthiol group for subsequent gold surface modification. The formation of self-assembled monolayers (SAMs) with these complex molecular architectures are thoroughly demonstrated by employing a combination of different techniques, including infrared reflection absorption spectroscopy, ellipsometry, contact angle, and cyclic voltammetry measurements. The immobilized heterobimetallic systems show fast electron-transfer kinetics and, hence, are capable of fast electrochemical response. In addition, the characteristic electrochemical signals of the SAMs were found to be sensitive to the presence of lanthanide centers at the bipyridyl terminal units. A positive shift of the potential of the redox signal is readily observed for lanthanide complexes compared to the bare organometallic ligand. This effect is equally observed for preformed complexes and on-surface complexation. Thus, an efficient ligating recruitment of europium and ytterbium cations at gold-modified electrodes is demonstrated, allowing for an easy electrochemical detection of the lanthanide ions along with an alternative preparative method of SAMs incorporating lanthanide cations compared to the immobilization of the preformed complex.

Iron fumarate as large-capacity and long-life anode material for Li-ion battery boosted by conductive Fe2P decorating

Due to the always accompanied huge volume change during cycling, it is still a great challenge to achieve stable large-capacity anode for Li-ion battery. Herein, iron fumarate has been exploited as a novel and promising anode material, which has the inherent advantages of low cost and eco-friendliness. During charge-discharge cycling, the flexible organic fumarate ligands act as high-efficient buffer materials to accommodate the volume change of Fe-based active species. Through in-situ conductive Fe2P decorating, the bulk electronic conductivity of the iron fumarate-based anode material can be effectively improved to achieve fast electrochemical response. Consequently, the iron fumarate-based anode material shows excellent structure stability with a capacity fading as low as 0.03% per cycle after 1400 cycles at 3.0 A g−1 and achieves superior rate performance with a high capacity of 520 mAh g−1 at 8.0 A g−1. This study suggests that iron fumarate is a potential anode material for large-scale applications.

Development of Biosensor-Based Device for Urea Concentration Measurement in Industrial Fertilizer Samples

In this presentation, we will demonstrate creation process (R&D and engineering) of biosensor and device for direct urea concentration measurement in industrial fertilizer samples. The analyzer is fully automatic, fast, not requiring professional assistance, compact and mobile. The breakthrough technology enabling the construction of such device is amperometric urea biosensor electrode, re-purposed from the biosensor suited for monitoring hemodialysis patients developed earlier by our team. There is no direct competitor for the device – fertilizer production and supply companies have to measure urea in their products by manual, labor-intensive techniques such as Kjeldahl method, where single measurement takes at least an hour, thus creating a beneficial market window for rapid and accurate industrial urea analyzer. Direct urea concentration measurement in water media has been a scientific challenge for decades. It is possible to measure urea concentration by spectrophotometry, but only in transparent, homogeneous and single compound solutions. A target media, concentrated ammonium nitrate – urea solution (UAN), is widely used fertilizer standard in agriculture, and in this case rapid determination of urea in product is complicated. A good technique for such urea measurement would be biosensors; however, urea breakdown does not involve electron exchange with external electrode, so for a long time the potentiometric electrodes were employed, where urea breakdown causes polarization changes of enzyme-covered surface. Such sensors exhibit fast electrochemical response, but have drawbacks - influence of media pH and high ionic strength to measurement errors, low sensitivity in low analyte concentrations (usually not less than 0.01 mM). Another option, ion-sensitive field-effect transistor electrodes adequately measure the current proportional to urea concentration, but usually lack reliability and are prone to permeability problems. Our suggested technology enabling the construction of such device - amperometric urea biosensor, constructed as a membrane to be fitted on working electrode surface. Its benefits - stability, insensitivity to pH or high ionic strength, low production cost, substrate selectivity, can be used constantly in enzyme-degrading fertilizer media for at least two weeks. It works at 0.2 V vs NHE potential, thus does not suffer of potentially significant electrochemical noise. It can measure urea concentration by declared accuracy of 5 %, when the automatic calibration is performed every 3 hours. The biosensor element – a membrane, fitted on the end of graphite electrode – works for 3 months, resulting in single measurement price under one cent. The reiterative measurement is implemented by magnetically stirred flow-through electrochemical cell with opening on top for sample entry. A double-flow peristaltic pump is designed to wash the cell and pre-fill the buffer solution for introduction of 50 µl of 1:1000 (v/v) pre-diluted sample. Currently, our team has developed the technology up to a final product trial batch of biosensor and analyzer device. In the presentation we will demonstrate the biosensor design and electrochemical properties, as well as design of device appliances developed such as electrochemical cell and double-flow peristaltic pump. Figure 1

A Determination Approach for Rivastigmine by Lepidocrocite Nanoparticles Supported on N-Chitosan Carbon Nanosheets/Anti-Fouling PAS: Application to Biosensing

In the present work, a triple amplified biosensor was constructed for ultrasensitive and selective analysis of an acetylcholinesterase inhibitor; rivastigmine (RIV) in human serum. The modified biosensor based on fabrication of pencil graphite electrode (PGE) with lepidocrocite nanoparticles (γ-FeOOH) dispersed in N-chitosan carbon nanosheets (N@CCNS). Pyrrolidinium acid sulfate (PAS) as an ionic liquid was added to amplify the signal of RIV. The physical properties of the modified electrodes were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy. The cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) were used to evaluate the performance of the modified electrode. Parameters affecting performance of the modified sensor were evaluated such as pH, scan rate, casting volume, concentration of nanocomposite …etc. The modified sensor showed a fast and sensitive electrochemical response to RIV sensing with wide linear range (3.0–90.0 nM), low detection limit (0.99 nM) and excellent anti-interference ability. Moreover, the fabricated sensor was successfully applied for determination of RIV in pharmaceutical tablets and spiked human serum and the obtained results are quite satisfactory.

Sonochemical driven simple preparation of nitrogen-doped carbon quantum dots/SnO2 nanocomposite: A novel electrocatalyst for sensitive voltammetric determination of riboflavin

We report a simple preparation of novel nanocomposite for the sensitive determination of riboflavin (RF) in real samples. Nitrogen-doped carbon quantum dots/SnO2 (N-CQD/SnO2) nanocomposite was prepared using sonochemical approach and applied as a voltammetric sensor for the sensitive determination of RF for the first time. The crystallographic phase, functional groups, surface analysis, and elemental distribution were examined using XRD, FT-IR, HR-TEM and EDS spectroscopic techniques respectively. This N-CQD/SnO2 nanocomposite-modified electrode shows a fast and sensitive electrochemical response to RF sensing with a good sensitivity (2.496 μA μM−1 cm-2), wide linear range (0.05–306 μM), low detection limit (8 nM) and excellent anti-interference ability. Furthermore, the developed sensor was investigated in commercial riboflavin tablets and milk powder and obtained results are quite satisfactory.

Electrochemical polymerization, characterization and in-situ conductivity studies of poly-3,4-ortho-xylendioxythiophene (PXDOT)

The electrochemical polymerization of 3,4-ortho-xylendioxythiophene (XDOT) in acetonitrile on Pt electrode let to obtain stable and well-adhered conducting polymer films. The voltamperometric response of the poly-3,4-ortho-xylendioxythiophene (PXDOT) showed a mirror-image, indicating fast electron transfer (ΔEp = 60 mV), which is a rare phenomenon in thick layers of conducting polymers. The in-situ electrochemical conductance experiments showed that the maximal conductance for PXDOT is reached at lower potentials and with less hysteresis than the observed for PEDOT, confirming a fast electrochemical response of the polymer. This behavior could be attributed to the presence of the xylen-unit attached to the polymer chain, which generates an internal order on the oligomeric chains, forming channels that facilitate the mobility of the electrolyte ions during the charge/discharge processes. Additionally, PXDOT showed an irreversible cathodic process which does not correspond to an n-doping, nevertheless induce a polymer internal rearrangement, which causes a major change in the p-doping signal. This cathodic process thus, it was attributed to the reduction of intrachain charge-trapped that was produced during electropolymerization.

Fabrication of High Aspect Ratio Millimeter-Tall Free-Standing Carbon Nanotube-Based Microelectrode Arrays.

Microelectrode arrays of carbon nanotube (CNT)/carbon composite posts with high aspect ratio and millimeter-length were fabricated using carbon-nanotube-templated microfabrication with a sacrificial "hedge". The high aspect ratio, mechanical robustness, and electrical conductivity of these electrodes make them a potential candidate for next-generation neural interfacing. Electrochemical measurements were also demonstrated using an individual CNT post microelectrode with a diameter of 25 μm and a length of 1 mm to perform cyclic voltammetry on both methyl viologen and dopamine in a phosphate-buffered saline solution. In addition to detection of the characteristic peaks, the CNT post microelectrodes show a fast electrochemical response, which may be enabling for in vivo and/or in vitro measurements. The CNT post electrode fabrication process was also integrated with other microfabrication techniques, resulting in individually addressable electrodes.

Electrochemical detection of nitrite and ascorbic acid at glassy carbon electrodes modified with carbon nano-onions bearing electroactive moieties

In this work, we evaluate two novel surfaces for the simultaneous detection of nitrite and ascorbic acid in aqueous media. Glassy carbon electrodes were first modified with small carbon nano-onions (GCE/CNO) and further functionalized either by electrografting ortho-aminophenol (oAP) groups or by physical adsorption of thionine to give electroactive surfaces that were characterized by cyclic voltammetry. The modified surfaces exhibited a fast electrochemical response and were able to detect the presence of nitrite and ascorbic acid by amperometry. The presence of both CNOs and the electroactive moiety on the electrode surface enhanced the sensitivity and lowered the limit of detection of the determinations as compared to GCE modified only with oAP or thionine. The CNO-modified electrodes showed good reproducibility and stability with time and were applied in the detection of ascorbic acid in orange juice.

Electrocatalytic Activity and Electroanalytical Performance of Nanodiamond-Derived Carbon Nano-Onions

Carbon nano-onions (CNOs) are an emerging, novel class of carbon nanomaterials. A CNO is a 0-D carbon analogue of a 1-D carbon nanotube (CNT) and a 2-D graphene. It is composed of sp2-bonded, concentric carbon shells surrounding a hollow core. The curved morphology of a CNO loosens the conjugation along the graphene sheet and results in the change in electronic structure. The unique structure as well as surface chemical functional groups of CNOs will significantly influence physicochemical, electronic, and electrochemical properties.In this talk, the physicochemical and electrochemical properties of CNOs will be presented. First, morphology and microstructure of CNOs were characterized by scanning and transmission electron microscopies (SEM, TEM), X-ray diffraction (XRD), and Raman spectroscopy. Chemical composition and chemical functional groups were probed by X-ray photoelectron spectroscopy (XPS). Raman spectra of CNOs showed a large value of ID/IG ratio, indicating that carbon concentric shells of CNOs include defects, i.e., exposed edge planes. Second, heteroatomic doping of CNOs and its electrocatalytic activity toward oxygen reduction reaction will be presented, in comparison with other carbon nanomaterials. Last, redox activities and electron transfer kinetics of CNOs were studied. CNOs showed remarkable electrochemical activities for the detection of biologically important molecules (such as high sensitivity, high selectivity and fast ET kinetics). Electrochemical measurements were carried out with standard redox couples such as Ru(NH3)6 3+/2+, Fe2+/3+, IrCl6 2 - /3 - and Fe(CN)6 3-/4- as well as redox-active biomolecules such as dopamine, epinephrine, and norepinephrine. The results showed a stable and fast electrochemical response of CNOs for all of the redox analytes and often surpassed the performance of other carbon electrodes like carbon nanotubes, graphite nanoflakes, and glassy carbon.

Thermally driven metastable solid-solution Li0.5FePO4 in nanosized particles and its phase separation behaviors

Nanosized LiFePO4 particles easily show a fast electrochemical response that can be achieved via a non-equilibrium pathway. To understand this intriguing phase transition behavior in nanosized LiFePO4 particles, the metastable solid-solution phase was prepared by thermal treatment with a chemically delithiated nanosized Li0.5FePO4 sample. Thermal treatment makes all the nanosized particles transform easily to the metastable solid-solution phase because of the large thermal energy while an electrochemical reaction does not. The phase separation behavior of the metastable solid-solution sample (Li0.5FePO4) was investigated under various kinetic conditions to understand critical factors affecting the phase separation behavior of nanosized LiFePO4 particles. The main findings in this study are as follows. The first finding is that the depressed phase separation behavior of the metastable phase may originate from the nanoparticle effect, in which the formation of a second phase inside a nanosized particle is not energetically favored because of the large interfacial energy. Therefore, phase separation in nanosized particles occurs between particles rather than inside a particle. If there was no over-potential, such as in the relaxed pellet experiment or in the relaxed electrode experiment in the electrolyte, the metastable phase was quite stable showing no phase separation behavior even though efficient pathways for lithium ions and electrons were well developed. The second finding is that the phase separation behavior of the metastable phase actually depends on the over-potential. Under open circuit voltage (OCV) conditions, the metastable phase started to exhibit a slight structural change during a long relaxation time, about ten days. The slow change of the metastable phase may be due to the low driving force, less than 10 mV, which comes from the energetic difference between the two-phase state and the metastable phase. This indicates that the phase separation behavior may require a large over-potential. When a large over-potential was applied using an external current, phase separation of the metastable phase was achieved, indicating that the phase separation behavior may be related to activation processes. Furthermore, the requirement for a large over-potential indirectly shows that the spinodal decomposition is depressed in nanosized particles. Considering that phase separation in nanosized particles occurs between particles, the surface charge transfer reaction can be a limited reaction for achieving phase separation because it is an activated process and governed by the over-potential. Considering the understanding obtained from the phase separation behavior of the metastable phase, the phase transition behavior of nanosized LiFePO4 particles during charging/discharging can proceed via the metastable phase because there is no spinodal decomposition behavior in nanosized particles and the metastable phase is quite stable.

Detection of Circulating Cancer Cells Using Electrocatalytic Gold Nanoparticles

A rapid cancer cell detection and quantification assay, based on the electrocatalytic properties of gold nanoparticles towards the hydrogen evolution reaction, is described. The selective labeling of cancer cells is performed in suspension, allowing a fast interaction between the gold nanoparticle labels and the target proteins expressed at the cell membrane. The subsequent electrochemical detection is accomplished with small volumes of sample and user-friendly equipment through a simple electrochemical method that generates a fast electrochemical response used for the quantification of nanoparticle-labeled cancer cells. The system establishes a selective cell-detection assay capable of detecting 4 × 10(3) cancer cells in suspension that can be extended to several other cells detection scenarios.

A novel method to synthesize whisker-like Co(OH) 2 and its electrochemical properties as an electrochemical capacitor electrode

A loose whisker-like Co(OH) 2 was synthesized by means of polyethylene glycol 4000 as soft template under ultrasonic condition, and investigated as an active electrode material for electrochemical capacitors. The composition and microstructure of the as-prepared Co(OH) 2 were investigated by X-ray diffraction spectroscopy and transmission electron microscopy. The formation mechanism of the whisker-like Co(OH) 2 was attentively proposed based on Fourier transform infrared spectroscopy analysis. Electrochemical studies revealed that the whisker-like Co(OH) 2 delivered a specific capacitance of 325 F/g at a current density of 20 mA/cm 2 ( ca. 1.3 A/g) and even 279 F/g at 80 mA/cm 2 ( ca. 5.3 A/g) due to its special nanostructure, indicating its fast electrochemical response property. A capacitance attenuation of ca. 7% over 1000 cycles meant the good cyclic stability of the whisker-like Co(OH) 2 for electrochemical capacitors application.

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

AbstractA room temperature ionic liquid N‐butylpyridinium hexafluorophosphate (BPPF6) was used as a binder to make an ionic liquid modified carbon paste electrode (IL‐CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL‐CPE was carefully studied. The oxidation peak potential of AA on the IL‐CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL‐CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (ks) as 0.87 and 0.800 s−1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10−5 to 3.0×10−3 mol/L with the linear regression equation as Ip (μA)=−2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10−6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.