Showing papers on "Reference electrode published in 2013"

Bismuth nanoparticle decorating graphite felt as a high-performance electrode for an all-vanadium redox flow battery.

Abstract: Employing electrolytes containing Bi3+, bismuth nanoparticles are synchronously electrodeposited onto the surface of a graphite felt electrode during operation of an all-vanadium redox flow battery (VRFB). The influence of the Bi nanoparticles on the electrochemical performance of the VRFB is thoroughly investigated. It is confirmed that Bi is only present at the negative electrode and facilitates the redox reaction between V(II) and V(III). However, the Bi nanoparticles significantly improve the electrochemical performance of VRFB cells by enhancing the kinetics of the sluggish V(II)/V(III) redox reaction, especially under high power operation. The energy efficiency is increased by 11% at high current density (150 mA·cm–2) owing to faster charge transfer as compared with one without Bi. The results suggest that using Bi nanoparticles in place of noble metals offers great promise as high-performance electrodes for VRFB application.

Handbook of reference electrodes

Abstract: Electrode potentials.- Reference redox systems in non-aqueous systems and the relation of electrode potentials in non-aqueous and mixed solvents to standard potentials in water.- Liquid junction potentials.- Salt bridges and diaphragms.- Reference electrodes for aqueous solutions.- Reference Electrodes for Use in Nonaqueous Solutions.- Reference electrodes for ionic liquids and molten salts.- Reference Electrodes in Oxidic Glass Melts.- Reference electrodes for solid electrolyte devices.- Direct solid contact in reference electrodes.- Micro reference electrodes.- Conducting polymer based reference electrodes.- Screen-printed, disposable, reference electrodes.- Pseudo-reference electrodes.- The Kelvin Probe technique as reference electrode for application on thin and ultra-thin electrolyte films.

High performance platinum-free counter electrode of molybdenum sulfide–carbon used in dye-sensitized solar cells

Abstract: A high porous molybdenum sulfide–carbon (MoS2–C) hybrid film was prepared by using an in situ hydrothermal route. The MoS2–C hybrid film served as a low-cost and high efficient platinum-free counter electrode for a dye-sensitized solar cell (DSSC). The cyclic voltammetry, electrochemical impedance spectroscopy and Tafel curve analysis indicate that the MoS2–C electrode possesses low charge transfer resistance on the electrolyte–electrode interface, high electrocatalytic activity and fast reaction kinetics for the reduction of triiodide to iodide at the counter electrode, which is due to large specific surface area and special structure and compositions of MoS2–C film. A DSSC with the novel MoS2–C counter electrode achieve a high power conversion efficiency of 7.69% under standard light illumination, which exceeds that of the DSSC with a Pt counter electrode (6.74%).

A low-cost paper-based inkjet-printed platform for electrochemical analyses

Abstract: An electrode platform printed on a recyclable low-cost paper substrate was characterized using cyclic voltammetry. The working and counter electrodes were directly printed gold-stripes, while the reference electrode was a printed silver stripe onto which an AgCl layer was deposited electrochemically. The novel paper-based chips showed comparable performance to conventional electrochemical cells. Different types of electrode modifications were carried out to demonstrate that the printed electrodes behave similarly with conventional electrodes. Firstly, a self-assembled monolayer (SAM) of alkanethiols was successfully formed on the Au electrode surface. As a consequence, the peak currents were suppressed and no longer showed clear increase as a function of the scan rate. Such modified electrodes have potential in various sensor applications when terminally substituted thiols are used. Secondly, a polyaniline film was electropolymerized on the working electrode by cyclic voltammetry and used for potentiometric pH sensing. The calibration curve showed close to Nerstian response. Thirdly, a poly(3,4-ethylenedioxythiophene) (PEDOT) layer was electropolymerized both by galvanostatic and cyclic potential sweep method on the working electrode using two different dopants; Cl− to study ion-to-electron transduction on paper-Au/PEDOT system and glucose oxidase in order to fabricate a glucose biosensor. The planar paper-based electrochemical cell is a user-friendly platform that functions with low sample volume and allows the sample to be applied and changed by e.g. pipetting. Low unit cost is achieved with mask- and mesh-free inkjet-printing technology.

Paper-based electroanalytical devices with an integrated, stable reference electrode

Abstract: This paper describes the development of a referenced Electrochemical Paper-based Analytical Device (rEPAD) comprising a sample zone, a reference zone, and a connecting microfluidic channel that includes a central contact zone. We demonstrated that the rEPADs provide a simple system for direct and accurate voltammetric measurements that are referenced by an electrode with a constant, well-defined potential. The performance of the rEPADs is comparable to commercial electrochemical cells, and the layout can be easily integrated into systems that permit multiplexed analysis and pipette-free sampling. The cost of this portable device is sufficiently low that it could be for single-use, disposable applications, and its method of fabrication is compatible with that used for other paper-based systems.

On the Electrochemical Response of Porous Functionalized Graphene Electrodes

Abstract: Electrodes used in electroanalysis, which are based on carbonaceous nanomaterials such as carbon nanotubes or graphene, often exhibit large degrees of porosity. By systematically varying the morphology of functionalized graphene electrodes from nearly flat to highly porous, we demonstrate experimentally that minute amounts of electrode porosity have surprisingly significant effects on the apparent reaction kinetics as determined by cyclic voltammetry, both in the reversible and the irreversible regime. We quantify electrode porosity using a coulometric approach and, with the help of numerical simulations, determine the correlation between electrode pore volume and apparent electrode kinetics. We show that in the reversible and quasi-reversible regime, the voltamperometric response constitutes a superposition of thin film diffusion-related effects within the porous electrode and of the standard flat electrode response. For irreversible kinetics, however, we show that diffusive coupling between the electrode and the electrolyte can, under suitably chosen conditions, result in effective electrocatalytic behavior. Confirming past theoretical work by Compton and others, our experiments demonstrate that for a comparison of electroanalytical data obtained with different electrode materials it is not sufficient to only consider differences in the materials' chemical structure but equally important to take into account differences in electrode morphology.

An amperometric sensor based on ionic liquid and carbon nanotube modified composite electrode for the determination of nitrite in milk

Abstract: A novel carbon composite electrode has been fabricated using ionic liquid n-octylpyridinum hexafluorophosphate (OPFP) and single-walled carbon nanotube (SWCNT). This electrode combined the advantages of ionic liquid and SWCNT as well as the characteristics of the “bulk” composite electrodes. Compared with the commercial glassy carbon electrode (GCE) and the ionic liquid–graphite (IL-G) composite electrode, the ionic liquid–SWCNT (IL-SWCNT) composite electrode exhibited remarkable increase in the electron transfer rate for electroactive compound and significant decrease in the overpotential for the oxidation of nitrite. Based on the enhanced electrocatalytic activity for the oxidation of nitrite, a wide linear range from 1.0 μM to 12.0 mM with a low detection limit of 0.1 μM was obtained. Furthermore, the IL-SWCNT electrode was applied to determine nitrite levels in milk samples. Experimental results showed that the proposed electrode could be used as an effective and sensitive sensor for the determination of nitrite.

Pseudo-reference Electrodes

Abstract: Both the terms of pseudo-reference (literally “false” reference) electrode and quasi-reference (“almost” or “essentially”) electrode are used in the literature, often synonymously or interchangeably. The essential difference between a true reference electrode (as defined in Chap. 1) and a pseudo-reference electrode is the lack of thermodynamic equilibrium in the latter case. In many cases simply platinum or silver or Ag/AgCl wires serve as pseudo- or quasi-reference electrodes. Obviously, thermodynamic equilibrium cannot exist, since there is no common component (anion or cation) in the two adjacent phases. However, usually they are calibrated by a reference redox system by adding the internal reference during the experiments into the electrolyte (preferred) or measuring their potential after the experiments by using a reference redox system or a conventional reference electrode. Sometimes when a reference redox system (e.g., ferrocene or cobaltocane) is also used in situ, this reference electrode is called a quasi-reference electrode. These types of reference electrodes are used almost exclusively in nonaqueous systems (See Chaps. 2 and 6), in molten salts or at elevated temperatures, in ionic liquids (see Chap. 7), and mostly in three-electrode potentiostatic or potentiodynamic experiments. The advantages of the use of pseudo-reference electrodes are their simplicity, and because those are immersed directly into the electrolyte used in the cell, the ohmic resistance (impedance) effect is small, no liquid junction potential appears, and usually there is no contamination of the test solution by solvent molecules or ions that a conventional reference electrode might transfer. There are several disadvantages of the use of these reference electrodes. First is the lack of the thermodynamic equlibrium; therefore, one cannot calculate their potential. Second, because these are not ideally nonpolarizable electrodes, there is a shift of their potential during the measurements, which depends on the current density applied. Third, most pseudo-reference electrodes work over a limited range of conditions such as pH or temperature; outside of this range the electrodes’ behavior becomes unpredictable. However, it should be mentioned that, although under suitably selected conditions the potential of the pseudo-reference electrode, although unknown, might be surprisingly constant during the experiments.

Neutron reflectometry studies on the lithiation of amorphous silicon electrodes in lithium-ion batteries

Abstract: Neutron reflectometry is used to study in situ the intercalation of lithium into amorphous silicon electrodes. The experiments are done using a closed three-electrode electrochemical cell setup. As a working electrode, an about 40 nm thick amorphous silicon layer is used that is deposited on a 1 cm thick quartz substrate coated with palladium as a current collector. The counter electrode and the reference electrode are made of lithium metal. Propylene carbonate with 1 M LiClO4 is used as an electrolyte. The utility of the cell is demonstrated during neutron reflectometry measurements where Li is intercalated at a constant current of 100 μA (7.8 μA cm−2) for different time steps. The results show (a) that the change in Li content in amorphous silicon and the corresponding volume expansion can be monitored, (b) that the formation of the solid electrolyte interphase becomes visible and (c) that an irreversible capacity loss is present.

A Wireless Passive Sensor for Temperature Compensated Remote pH Monitoring

Abstract: Temperature must be accounted for in order to provide accurate measurements in electrode-based pH sensors. We present an integrated wireless passive sensor for remote pH monitoring employing temperature compensation. The sensor is a resonant circuit consisting of a planar spiral inductor connected in parallel to a temperature-dependent resistor (thermistor) and a voltage-dependent capacitor (varactor). A pH combination electrode consisting of an iridium/iridium oxide sensing electrode and a silver/silver chloride reference electrode, is connected in parallel with the varactor. A potential difference change across the electrodes due to pH variation of the solution changes the voltage-dependent capacitance and shifts the resonant frequency, while temperature of the solution affects the resistance and changes the quality factor of the sensor. An interrogator coil is inductively coupled to the sensor inductor and remotely tracks the resonant frequency and quality factor of the sensor. The sensor is calibrated for temperature over a range of 25 $^{\circ}{\rm C}$ –55 $^{\circ}{\rm C}$ and pH over a 1.5–12 dynamic range. By employing temperature compensation, a measurement accuracy of less than 0.1 pH is achieved and the response time of the sensor is demonstrated to be less than 1 s. The sensor overcomes the pH measurement error due to the temperature dependence of electrode-based passive pH sensors and has applications in remote pH monitoring where temperature varies over a wide range.

New approach to electrode kinetic measurements in square-wave voltammetry: amplitude-based quasireversible maximum.

Abstract: The influence of the potential pulse height of square-wave voltammetry (SWV) (i.e., the SW amplitude) is studied for a variety of quasireversible electrode mechanisms, including a simple solution-phase electrode reaction at a planar or spherical electrode, a solution phase electrode reaction coupled with a reversible follow-up chemical reaction, and a diffusionless surface confined electrode reaction. The electrode kinetics of all the electrode mechanisms depends critically on the SW amplitude, and the quasireversible kinetic region is a function of both frequency-related electrode kinetic parameters and the SW amplitude. Thus, a novel methodology for electrode kinetics measurements is proposed by altering the SW amplitude only, at a fixed frequency of the SW potential modulation, that is, at a constant scan rate of the voltammetric experiment. Electrode kinetic measurements at a constant SW frequency are of exceptional importance especially when complex electrode mechanisms are studied, which depend on several frequency-related kinetic parameters. The electrode kinetic measurements are based on a novel feature termed the "amplitude-based quasireversible maximum", manifested as a parabolic dependence of the amplitude-normalized net SW peak current versus the SW amplitude. The position of the amplitude-based quasireversible maximum depends on the standard rate constant of the electrode reaction, enabling estimation of this important kinetic parameter in a simple and fast procedure. The novel quasireversible maximum is attributed to all studied electrode mechanisms, implying that it is a general feature of most electrode mechanisms under conditions of SWV.

Fabrication of a Microneedle/CNT Hierarchical Micro/Nano Surface Electrochemical Sensor and Its In-Vitro Glucose Sensing Characterization

Abstract: We report fabrication of a microneedle-based three-electrode integrated electrochemical sensor and in-vitro characterization of this sensor for glucose sensing applications. A piece of silicon was sequentially dry and wet etched to form a 15 × 15 array of tall (approximately 380 µm) sharp silicon microneedles. Iron catalyst was deposited through a SU-8 shadow mask to form the working electrode and counter electrode. A multi-walled carbon nanotube forest was grown directly on the silicon microneedle array and platinum nano-particles were electrodeposited. Silver was deposited on the Si microneedle array through another shadow mask and chlorinated to form a Ag/AgCl reference electrode. The 3-electrode electrochemical sensor was tested for various glucose concentrations in the range of 3~20 mM in 0.01 M phosphate buffered saline (PBS) solution. The sensor's amperometric response to the glucose concentration is linear and its sensitivity was found to be 17.73 ± 3 μA/mM-cm2. This microneedle-based sensor has a potential to be used for painless diabetes testing applications.

Simultaneous determination of droxidopa and carbidopa using a carbon nanotubes paste electrode

Abstract: A novel carbon paste electrode modified with carbon nanotube and 5-amino-2’-ethyl -biphenyl-2-ol (5AEB) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of droxidopa and carbidopa, is described. Cyclic voltammetry was used to investigate the redox properties of this modified electrode at various scan rates. The apparent charge transfer rate constant, ks, and transfer coefficient, α, for electron transfer between 5AEB and carbon nanotubes paste electrode were calculated as 17.3 ± 0.1 s−1 and 0.5, respectively. The electrode was also employed to study the electrocatalytic oxidation of droxidopa, using cyclic voltammetry, chronoamperometry, square wave voltammetry and electrochemical impedance spectroscopy as diagnostic techniques. It has been found that the oxidation of droxidopa at the surface of modified electrode occurs at a potential of about 355 mV less positive than that of an unmodified CPE. The diffusion coefficient, electron transfer coefficient, and heterogeneous rate constant, for oxidation of droxidopa at the modified electrode surface were also determined. Square wave voltammetry exhibits a linear dynamic range from 1.2 × 10−7 to 2.25 × 10−4 M and a detection limit of 50.0 nM for droxidopa. Finally this modified electrode was used for simultaneous determination of droxidopa and carbidopa for the first time.