Showing papers on "Reference electrode published in 2012"

Exploring the large voltage range of carbon/carbon supercapacitors in aqueous lithium sulfate electrolyte

Abstract: This study investigates the large voltage range of symmetric carbon/carbon capacitors in environmentally friendly aqueous lithium sulfate electrolyte. A high over-potential related to the hydrogen sorption mechanism at the negative electrode contributes usefully to enhance the operating voltage up to 1.9 V with an excellent stability during 10 000 charge/discharge cycles. Such a voltage value is two times higher than the values generally demonstrated with symmetric carbon/carbon capacitors in conventional aqueous media, while avoiding the disadvantages of the corrosive properties of acidic and basic electrolytes. Temperature programmed desorption analysis of the electrodes after long-term cycling gives the evidence that the maximum voltage is essentially limited by an irreversible electro-oxidation process at the positive electrode. If the potential of the positive electrode goes beyond a given value during cell operation, a massive electro-oxidation of carbon leads to a further deleterious increase of the maximum potential of the electrode and an increase of electrode resistance resulting in a decrease of capacitance. Inconvenience can be sidestepped by performing a controlled chemical oxidation of the carbon surface using hydrogen peroxide. As a consequence, the maximum potential of the electrode remains stable during operation of the cell at 1.9 V, and the system can be charged/discharged during 10 000 cycles with very moderate loss of capacitance or increase of resistance.

Self-cleaning and vibration wave energy digestion link containing electrogenerated chemiluminescence analyzing and detecting device

Abstract: The invention relates to a self-cleaning and vibration wave energy digestion link containing electrogenerated chemiluminescence analyzing and detecting device and belongs to the field of analyzing and testing. The technical scheme is mainly specific to a problem that glassy carbon electrodes are susceptible to adsorption pollution in prior devices. The device comprises an electrolytic tank, a glassy carbon electrode, a counter electrode and a reference electrode and is characterized by further comprising a tubular ultrasonic probe and a ultrasonic energy absorber which is made of microporous materials and is in a pen cap shape or a test tube shape, wherein the glassy carbon electrode, the counter electrode and the reference electrode are inserted into the electrolytic tank, a ring-shaped piezoelectric element is embedded on the end portion of the tubular ultrasonic probe, an electrode post of the glassy carbon electrode is sleeved on a hollow pipeline in the tubular ultrasonic probe in a sliding mode, the end face of a glassy carbon electrode working end is in a same plane with the end face of a working end of the tubular ultrasonic probe, and a working end of the reference electrode extends into an inner chamber of the ultrasonic energy absorber. By means of the device, a prompt ultrasonic cleaning operation which is specific to the glassy carbon electrode can be achieved, besides, depending on the ultrasonic energy absorber, the comprehensive interference of ultrasonic waves with the reference electrode can be inhibited.

Boron-based electrolyte solutions with wide electrochemical windows for rechargeable magnesium batteries

Abstract: Recently, we have developed a boron based electrolyte system with outstanding electrochemical performance, formed through the reaction of tri(3,5-dimethylphenyl)borane (Mes3B) and PhMgCl in THF, for rechargeable magnesium batteries. In this paper, the main components and equilibria of the unique boron based electrolyte solutions are identified by NMR, single-crystal XRD, etc. The results prove that the solutions contain various magnesium species, such as Mg2Cl3+, MgCl+, Ph2Mg and the tetracoordinated boron anion [Mes3BPh]−. Fluorescence spectra and Raman spectroscopy analyses indicate that the high anodic stability (ca. 3.5 V vs. Mg reference electrode (RE)) of the Mes3B–(PhMgCl)2 electrolyte is attributed to the non-covalent interactions between the anion [Mes3BPh]− and Ph2Mg. Furthermore, the air sensitivity of the boron based electrolyte and its electrochemical stability on the different current collectors are studied. Finally, the reversible electrochemical process of Mg intercalation into a Mo6S8 cathode confirms that the boron based electrolyte could be practically used in rechargeable Mg battery systems.

Dynamic potential–pH diagrams application to electrocatalysts for water oxidation

Abstract: The construction and use of “dynamic potential–pH diagrams” (DPPDs), that are intended to extend the usefulness of thermodynamic Pourbaix diagrams to include kinetic considerations is described. As an example, DPPDs are presented for the comparison of electrocatalysts for water oxidation, i.e., the oxygen evolution reaction (OER), an important electrochemical reaction because of its key role in energy conversion devices and biological systems (water electrolyses, photoelectrochemical water splitting, plant photosynthesis). The criteria for obtaining kinetic data are discussed and a 3-D diagram, which shows the heterogeneous electron transfer kinetics of an electrochemical system as a function of pH and applied potential is presented. DPPDs are given for four catalysts: IrO2, Co3O4, Co3O4 electrodeposited in a phosphate medium (Co–Pi) and Pt, allowing a direct comparison of the activity of different electrode materials over a broad range of experimental conditions (pH, potential, current density). In addition, the experimental setup and the factors affecting the accurate collection and presentation of data (e.g., reference electrode system, correction of ohmic drops, bubble formation) are discussed.

Electrochemical Reduction of Carbon Dioxide Using a Copper Rubeanate Metal Organic Framework

Abstract: We synthesized a copper rubeanate metal organic framework (CR-MOF) which has the potential to improve the catalytic activity of electrochemical reduction of CO2 due to its characteristics of electronic conductivity, proton conductivity, dispersed reaction sites, and nanopores. Synthesized CR-MOF particles were dropped on carbon paper (CP) to form a working electrode. The onset potential for CO2 reduction of a CR-MOF electrode was about 0.2 V more positive than that observed on a Cu metal electrode in an aqueous electrolyte solution. Our analysis of the reduction products during potentiostatic electrolysis showed formic acid (HCOOH) to be virtually the only CO2 reduction product on a CR-MOF electrode, whereas a Cu metal electrode generates a range of products. The quantity of products from the CR-MOF electrode was markedly greater (13-fold at −1.2 V vs. SHE) than that of a Cu metal electrode. Its stability was also confirmed.

User-Friendly Differential Voltage Analysis Freeware for the Analysis of Degradation Mechanisms in Li-Ion Batteries

Abstract: A user-friendly differential voltage analysis software has been developed and is described here. High-precision reference potential-specific capacity data for Li/negative electrode and Li/positive electrodes, as well as the cycled full cell potential-specific capacity, must be supplied by the user. From these, the differential voltage versus capacity, dV/dQ vs. Q, of a full Li-ion cell is calculated and compared to experiment. The calculated dV/dQ vs. Q curve has four adjustable parameters which are optimized manually with slider bars or automatically by least squares fitting of the calculation to experiment. The parameters are the positive electrode mass, the negative electrode mass, the positive electrode slippage and the negative electrode slippage. Examples of the use of the program are given for graphite/LiCoO2 wound cells cycled for hundreds of cycles. The variation of the four parameters with cycle number give insights into the mechanisms of cell failure equivalent to that which could be obtained with a Li reference electrode inserted within the cell. The software is available free of charge by contacting the authors.

Application of Electrochemically Reduced Graphene Oxide on Screen-Printed Ion-Selective Electrode

Abstract: In this study, a novel disposable all-solid-state ion-selective electrode using graphene as the ion-to-electron transducer was developed. The graphene film was prepared on screen-printed electrode directly from the graphene oxide dispersion by a one-step electrodeposition technique. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to demonstrate the large double layer capacitance and fast charge transfer of the graphene film modified electrode. On the basis of these excellent properties, an all-solid-state calcium ion-selective electrode as the model was constructed using the calcium ion-selective membrane and graphene film modified electrode. The mechanism about the graphene promoting the ion-to-electron transformation was investigated in detail. The disposable electrode exhibited a Nernstian slope (29.1 mV/decade), low detection limit (10–5.8 M), and fast response time (less than 10 s). With the high hydrophobic character of graphene materials, no water film was formed between...

Influence of the counter electrode on the photovoltaic performance of dye-sensitized solar cells using a disulfide/thiolate redox electrolyte

Abstract: Strong scientific interests focus on the investigation of iodine-free redox couples for their application in dye-sensitized solar cells (DSCs). Recently, a disulfide/thiolate-based redox electrolyte has been proposed as a valuable alternative to the conventional I3−/I− system due to its transparent and non-corrosive nature. In the work presented herein, we systematically studied the influence of different counter electrode materials on the photovoltaic performance of DSCs employing this promising organic redox electrolyte. Our investigations focused on understanding the importance of electrocatalytic activity and surface area of the electroactive material on the counter electrode, comparing the conventional platinum to cobalt sulfide (CoS) and poly(3,4-ethylenedioxythiophene) (PEDOT). Electrochemical Impedance Spectroscopy has been used to study in detail the interfacial charge transfer reaction at the counter electrode. By using a high surface area PEDOT-based counter electrode, we finally achieved an unprecedented power conversion efficiency of 7.9% under simulated AM1.5G solar irradiation (100 mW cm−2) which, to the best of our knowledge, represents the highest efficiency that has so far been reported for an organic redox couple.

Single-Molecule Electrochemical Gating in Ionic Liquids

Abstract: The single-molecular conductance of a redox active molecular bridge has been studied in an electrochemical single-molecule transistor configuration in a room-temperature ionic liquid (RTIL). The redox active pyrrolo-tetrathiafulvalene (pTTF) moiety was attached to gold contacts at both ends through −(CH2)6S– groups, and gating of the redox state was achieved with the electrochemical potential. The water-free, room-temperature, ionic liquid environment enabled both the monocationic and the previously inaccessible dicationic redox states of the pTTF moiety to be studied in the in situ scanning tunneling microscopy (STM) molecular break junction configuration. As the electrode potential is swept to positive potentials through both redox transitions, an ideal switching behavior is observed in which the conductance increases and then decreases as the first redox wave is passed, and then increases and decreases again as the second redox process is passed. This is described as an “off–on–off–on–off” conductance ...

Amperometric determination of xanthine in fish meat by zinc oxide nanoparticle/chitosan/multiwalled carbon nanotube/polyaniline composite film bound xanthine oxidase

Abstract: Xanthine oxidase (XOD) was immobilized on a composite film of zinc oxide nanoparticle/chitosan/carboxylated multiwalled carbon nanotube/polyaniline (ZnO-NP/CHIT/c-MWCNT/PANI) electrodeposited over the surface of a platinum (Pt) electrode. A xanthine biosensor was fabricated using XOD/ZnO-NP/CHIT/c-MWCNT/PANI/Pt as working electrode, Ag/AgCl as reference electrode and Pt wire as auxiliary electrode connected through a potentiostat. The ZnO-NPs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the enzyme electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). The biosensor showed optimum response within 4 s at 0.5 V potential, pH 7.0, 35 °C and linear range 0.1–100 μM with a detection limit of 0.1 μM. The enzyme electrode was employed for determination of xanthine in fish meat during storage. The electrode lost 30% of its initial activity after 80 uses over one month, when stored at 4 °C.

Improved electrochemical microsensor for the real-time simultaneous analysis of endogenous nitric oxide and carbon monoxide generation.

Abstract: An amperometric dual NO/CO microsensor was developed on the basis of a working electrode incorporating dual Pt microdisks (each diameter, 76 μm) and a Ag/AgCl reference electrode covered with a gas permeable membrane. One of the Pt disks was sequentially electrodeposited with Pt and Sn; the other Pt disk was deposited with Pt–Fe(III) oxide nanocomposites. The first showed activity for the oxidation of both NO and CO; the second showed activity only for NO oxidation. In the copresence of NO and CO, the currents measured at each electrode, respectively, represented the concentrations of CO and NO. The sensor showed high stability during the monitoring of organ tissue for at least 2.5 h and high selectivity to NO over CO at the Pt–Fe(III) oxide working electrode. Real-time coupled dynamic changes of NO and CO generated by a living C57 mouse kidney were monitored simultaneously and quantitatively in response to a NO synthase inhibitor (NG-nitro-l-arginine methyl ester), for the first time. CO was found to inc...

Electrochemical immunosensor modified with self-assembled monolayer of 11-mercaptoundecanoic acid on gold electrodes for detection of benzo[a]pyrene in water.

Abstract: Well-oriented bio-conjugates on gold electrode surfaces will indirectly influence the molecular recognition of antigens to surface bound antibodies thus improving the detection performance of electrochemical immunosensors This paper describes the modification of self-assembled monolayers (SAMs) on gold electrode surface with 11-mercaptoundecanoic acid (11-MUA) Activation of carboxylic acid terminal was performed by reaction of a mixture of water soluble carbodiimide and N-hydrosuccinimide (NHS) on the electrode surfaces Characterisation of the SAM formation on the gold electrode was performed using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and contact angle measurements An amperometric immunosensor was developed for the screening of polycyclic aromatic hydrocarbons (PAHs) in water The system consists of gold as the working electrode, platinum as the counter electrode and a Ag/AgCl reference electrode This three electrode system is integrated on a single chip The measurement employs the enzyme-linked immunosorbent assay (ELISA) principle Benzo[a]pyrene (BaP) was detected using an immunological reaction by measuring the alkaline phosphatase (AP) enzymatic reaction towards the substrate para-amino phenyl phosphate (pAPP) A competitive assay was performed within the electrode using AP as the labelled-enzyme A lower limit of detection (56 ng ml−1) of BaP was achieved after the activation of the mixture of carbodiimide and succinimide with the alkanethiol SAM on the gold electrode in comparison to that obtained for the unmodified electrode (142 ng ml−1) The developed surface functionalised sensor demonstrated acceptable reproducibility and good stability, with a wide linear response to BaP (4–140 ng ml−1)

A Potentiometric Indirect Uric Acid Sensor Based on ZnO Nanoflakes and Immobilized Uricase

Abstract: In the present work zinc oxide nanoflakes (ZnO-NF) structures with a wall thickness around 50 to 100 nm were synthesized on a gold coated glass substrate using a low temperature hydrothermal method. The enzyme uricase was electrostatically immobilized in conjunction with Nafion membrane on the surface of well oriented ZnO-NFs, resulting in a sensitive, selective, stable and reproducible uric acid sensor. The electrochemical response of the ZnO-NF-based sensor vs. a Ag/AgCl reference electrode was found to be linear over a relatively wide logarithmic concentration range (500 nM to 1.5 mM). In addition, the ZnO-NF structures demonstrate vast surface area that allow high enzyme loading which results provided a higher sensitivity. The proposed ZnO-NF array-based sensor exhibited a high sensitivity of ~66 mV/ decade in test electrolyte solutions of uric acid, with fast response time. The sensor response was unaffected by normal concentrations of common interferents such as ascorbic acid, glucose, and urea.

Electrogenerated Chemiluminescence for Potentiometric Sensors

Abstract: We report here on a generic approach to read out potentiometric sensors with electrogenerated chemiluminescence (ECL). In a first example, a potassium ion-selective electrode acts as the reference electrode and is placed in contact with the sample solution. The working electrode of the three-electrode cell is responsible for ECL generation and placed in a detection solution containing tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)32+] and the coreactant 2-(dibutylamino)ethanol (DBAE), physically separated from the sample by a bridge. Changes in the sample potassium concentration directly modulate the potential at the working electrode, and hence the ECL output, when a constant-potential pulse is applied between the two electrodes. A linear response of the ECL intensity to the logarithmic potassium concentration between 10 μm and 10 mM was found.

True Reference Nanosensor Realized with Silicon Nanowires

Abstract: Conventional gate oxide layers (e.g., SiO2, Al2O3, or HfO2) in silicon field-effect transistors (FETs) provide highly active surfaces, which can be exploited for electronic pH sensing. Recently, great progress has been achieved in pH sensing using compact integrateable nanowire FETs. However, it has turned out to be much harder to realize a true reference electrode, which – while sensing the electrostatic potential – does not respond to the proton concentration. In this work, we demonstrate a highly effective reference sensor, a so-called reference FET, whose proton sensitivity is suppressed by as much as 2 orders of magnitude. To do so, the Al2O3 surface of a nanowire FET was passivated with a self-assembled monolayer of silanes with a long alkyl chain. We have found that a full passivation can be achieved only after an extended period of self-assembling lasting several days at 80 °C. We use this slow process to measure the number of active proton binding sites as a function of time by a quantitative com...

Transport of redox probes through single pores measured by scanning electrochemical-scanning ion conductance microscopy (SECM-SICM).

Abstract: We report scanning electrochemical microscopy-scanning ion conductance microscopy (SECM-SICM) experiments that describe transport of redox active molecules which emanate from single pores of a track-etch membrane. Experiments are performed with electrodes which consist of a thin gold layer deposited on one side of a nanopipet. Subsequent insulation of the electrode with parylene results in a hybrid electrode for SECM-SICM measurements. Electrode fabrication is straightforward and highly parallel. For image collection, ionic current measured at the nanopipet both controls the position of the electrode with respect to the membrane surface and reports the local conductance in the vicinity of the nanopipet, while faradaic current measured at the Au electrode reports the presence of redox-active molecules. Application of a transmembrane potential difference affords additional control over migration of charged species across the membrane.