Showing papers on "Reference electrode published in 2015"

Photoluminescence‐Tunable Carbon Nanodots: Surface‐State Energy‐Gap Tuning

Abstract: A controllable wet oxidation method for synthesizing excitation-independent C-dots with tunable fluorescent colors was developed. carbon fibers (CFs) were added to a nitric acid solution. Then, the well-stirred solution was heated to 120°C and refluxed for 48 h. The corresponding solution containing C-dots was collected at a given time and then neutralized with NaOH. The resulting solution was first filtered by membrane filters and then ultrafiltered successively. The ECL experiments were conducted in a three-electrode electrochemical system with a Pt-disk working electrode, a Pt-wire counter electrode, and an Ag/AgCl reference electrode. The results revealed that the PL properties of C-dots, mainly influenced by their size and degree of surface oxidation, can be tuned by varying reaction time, temperature, and concentration of nitric acid. The energy gap of the surface states, where electrons and holes recombine to emit fluorescence, correlated with the extent of the π-electron system and surface chemistry.

Carbon Nanotube Chemiresistor for Wireless pH Sensing

Abstract: The ability to accurately measure real-time pH fluctuations in-vivo could be highly advantageous. Early detection and potential prevention of bacteria colonization of surgical implants can be accomplished by monitoring associated acidosis. However, conventional glass membrane or ion-selective field-effect transistor (ISFET) pH sensing technologies both require a reference electrode which may suffer from leakage of electrolytes and potential contamination. Herein, we describe a solid-state sensor based on oxidized single-walled carbon nanotubes (ox-SWNTs) functionalized with the conductive polymer poly(1-aminoanthracene) (PAA). This device had a Nernstian response over a wide pH range (2–12) and retained sensitivity over 120 days. The sensor was also attached to a passively-powered radio-frequency identification (RFID) tag which transmits pH data through simulated skin. This battery-less, reference electrode free, wirelessly transmitting sensor platform shows potential for biomedical applications as an implantable sensor, adjacent to surgical implants detecting for infection.

All-solid-state reference electrodes based on colloid-imprinted mesoporous carbon and their application in disposable paper-based potentiometric sensing devices.

Abstract: Reference electrodes are used in almost every electroanalytical measurement. Here, all-solid-state reference electrodes are described that employ colloid-imprinted mesoporous (CIM) carbon as solid contact and a poly(vinyl chloride) reference membrane to contact the sample. Such a reference membrane is doped with a moderately hydrophilic ionic liquid and a hydrophobic redox couple, leading to well-defined constant potentials at the interfaces of this membrane to the sample and to the solid contact, respectively. Due to the intrinsic properties of CIM carbon, reference electrodes with a CIM carbon solid contact exhibit excellent resistance to common interfering agents such as light and O2, with outstanding potential stability in continuous potentiometric measurements. The potential drift of CIM carbon-based reference electrodes without redox couple is as low as 1.7 μV/h over 110 h, making them the most stable all-solid-state reference electrodes reported so far. To demonstrate the compatibility of CIM carbo...

High Performance Flexible Supercapacitor Electrodes Composed of Ultralarge Graphene Sheets and Vanadium Dioxide

Abstract: Little is known regarding the effect of the graphene lateral size on the electrochemical performance of hybrid graphene electrode. This work examines the electrochemical performance of a flexible hybrid supercapacitor electrode composed of ultralarge graphene oxide (UGO; mean lateral size of 47 ± 22 μm) and vanadium dioxide (VO2) nanobelts, referring to a reference electrode composed of small scale graphene oxide (SGO; mean lateral size of 0.8 ± 0.5 μm) and VO2.Thermal treatment converts UGO/VO2 and SGO/VO2 to URGO/VO2 (denoted VURGO) and SRGO/VO2 (denoted VSRGO) electrodes, respectively. The sheet resistance of the VURGO film (0.57 ± 0.03 kΩ sq.–1) was two orders of magnitude lower than that of the VSRGO (55.74 ± 9.35 kΩ sq.–1). The VURGO hybrid electrode showed a specific capacitance of 769 F g−1, which was significantly better than the corresponding values for the VSRGO electrode (385 F/g). These results support the notion that the use of ultralarge graphene sheets (≈22 500 μm2) lowers the intersheet resistance due to the presence of fewer intersheet tunneling barriers. This article highlights the potential utility of URGO (as a conductive support) in hybrid electrode containing VO2 nanobelts for high performance flexible hybrid supercapacitor.

On-chip highly sensitive saliva glucose sensing using multilayer films composed of single-walled carbon nanotubes, gold nanoparticles, and glucose oxidase

Abstract: It is very important for human health to rapidly and accurately detect glucose levels in biological environments, especially for diabetes mellitus. We proposed a simple, highly sensitive, accurate, convenient, low-cost, and disposable glucose biosensor on a single chip. A working (sensor) electrode, a counter electrode, and a reference electrode are integrated on a single chip through micro-fabrication. The working electrode is functionalized through a layer-by-layer (LBL) assembly of single-walled carbon nanotubes (SWNTs) and multilayer films composed of chitosan (CS), gold nanoparticles (GNp), and glucose oxidase (GOx) to obtain high sensitivity and accuracy. The glucose sensor has following features: (1) direct electron transfer between GOx and the electrode surface; (2) on-a-chip; (3) glucose detection down to 0.1 mg/dL (5.6 μM); (4) good sensing linearity over 0.017–0.81 mM; (5) high sensitivity (61.4 μA/mM-cm2) with a small reactive area (8 mm2); (6) fast response; (7) high reproducibility and repeatability; (8) reliable and accurate saliva glucose detection. Thus, this disposable biosensor will be an alternative for real time tracking of glucose levels from body fluids, e.g. saliva, in a noninvasive, pain-free, accurate, and continuous way. In addition to being used as a disposable glucose biosensor, it also provides a suitable platform for on-chip electrochemical sensing for other chemical agents and biomolecules.

High Energy Density Aqueous Electrochemical Capacitors with a KI-KOH Electrolyte.

Abstract: We report a new electrochemical capacitor with an aqueous KI-KOH electrolyte that exhibits a higher specific energy and power than the state-of-the-art nonaqueous electrochemical capacitors. In addition to electrical double layer capacitance, redox reactions in this device contribute to charge storage at both positive and negative electrodes via a catholyte of IOx–/I– couple and a redox couple of H2O/Had, respectively. Here, we, for the first time, report utilizing IOx–/I– redox couple for the positive electrode, which pins the positive electrode potential to be 0.4–0.5 V vs Ag/AgCl. With the positive electrode potential pinned, we can polarize the cell to 1.6 V without breaking down the aqueous electrolyte so that the negative electrode potential could reach −1.1 V vs Ag/AgCl in the basic electrolyte, greatly enhancing energy storage. Both mass spectroscopy and Raman spectrometry confirm the formation of IO3– ions (+5) from I– (−1) after charging. Based on the total mass of electrodes and electrolyte in ...

Novel Ion-to-Electron Transduction Principle for Solid-Contact ISEs

Abstract: Solid-contact ion-selective electrodes (SC-ISEs) are traditionally employed as potentiometric sensors, where the ion activity is related to the zero-current potential of the sensor versus the reference electrode. In this communication, an alternative ion-to-electron transduction principle for SC-ISEs is introduced. The suggested signal transduction principle resembles “constant-potential coulometry” utilizing the redox capacitance of the internal solid contact in order to convert changes in ion concentration (activity) into electrical current and charge. This short communication provides proof-of-concept for the suggested signal transduction method for SC-ISEs utilizing poly(3,4-ethylenedioxythiphene) (PEDOT) as the solid contact that was coated with a cation-sensitive polymeric membrane.

On the electrochemical origin of the enhanced charge acceptance of the lead–carbon electrode

Abstract: Bi-functional electrode materials, composed of capacitive activated carbon (AC) and battery electrode materials, possess higher power performance than traditional battery electrode materials. Negative electrodes of lead acid batteries with AC additives (i.e., lead–carbon electrodes) display much better charge acceptance than do traditional lead negative electrodes, and are suitable for energy storage in hybrid electrical vehicles. In this paper, we discuss the electrochemical processes on AC in lead–carbon electrodes. In the charging process of the lead–carbon electrode, lead electrodeposits on AC at potentials higher than the open circuit potential of lead, and the large surface area of AC provides extra active sites for lead electrodeposition and the growth of the electrochemical active surface area of lead. Namely, AC acts as an electron bumper and electron distributor in the charging process of the lead–carbon electrode. Most importantly, at high charge rates, the hydrogen evolution reaction (HER) on AC is prohibited by reversible hydrogen adsorption; and meanwhile the adsorbed hydrogen contributes to the charging process.

Paper-based microfluidic sampling for potentiometric determination of ions

Abstract: In this work, paper-based microfluidic sampling was used together with potentiometric determination of ions (Cd2+, Cl−, Pb2+) and pH Calibration solutions and samples were absorbed into paper substrates and potentiometric detection was performed by placing solid-state ion-selective electrodes (ISEs) and a reference electrode in direct contact with the paper substrate The paper substrate was found to influence the determination of Pb2+ at low concentrations, indicating complexation of Pb2+ by chemically active groups present in paper Paper-based microfluidic sampling was successfully applied in measurements of pH in various foodstuffs and environmental samples by employing a conventional pH glass electrode However, some influence of the paper substrate on the measured pH was observed for samples with pH close to neutral Despite some limitations, paper-based microfluidic sampling with potentiometric sensing opens new possibilities for direct chemical analysis of specific sample types The method described in this work is particularly interesting for analysis of small sample volumes with a high content of solid impurities and for analysis of eg liquid or moisture from polluted surfaces and foodstuff

Pre-lithiation of electrode materials in a semi-solid electrode

Abstract: Embodiments described herein relate generally to electrochemical cells having pre-lithiated semi-solid electrodes, and particularly to semi-solid electrodes that are pre-lithiated during the mixing of the semi-solid electrode slurry such that a solid-electrolyte interface (SEI) layer is formed in the semi-solid electrode before the electrochemical cell formation. In some embodiments, a semi-solid electrode includes about 20% to about 90% by volume of an active material, about 0% to about 25% by volume of a conductive material, about 10% to about 70% by volume of a liquid electrolyte, and lithium (as lithium metal, a lithium-containing material, and/or a lithium metal equivalent) in an amount sufficient to substantially pre-lithiate the active material. The lithium metal is configured to form a solid-electrolyte interface (SEI) layer on a surface of the active material before an initial charging cycle of an electrochemical cell that includes the semi-solid electrode.

A solid-state thin-film Ag/AgCl reference electrode coated with graphene oxide and its use in a pH sensor.

Abstract: In this study, we describe a novel solid-state thin-film Ag/AgCl reference electrode (SSRE) that was coated with a protective layer of graphene oxide (GO). This layer was prepared by drop casting a solution of GO on the Ag/AgCl thin film. The potential differences exhibited by the SSRE were less than 2 mV for 26 days. The cyclic voltammograms of the SSRE were almost similar to those of a commercial reference electrode, while the diffusion coefficient of Fe(CN)63− as calculated from the cathodic peaks of the SSRE was 6.48 × 10−6 cm2/s. The SSRE was used in conjunction with a laboratory-made working electrode to determine its suitability for practical use. The average pH sensitivity of this combined sensor was 58.5 mV/pH in the acid-to-base direction; the correlation coefficient was greater than 0.99. In addition, an integrated pH sensor that included the SSRE was packaged in a secure digital (SD) card and tested. The average sensitivity of the chip was 56.8 mV/pH, with the correlation coefficient being greater than 0.99. In addition, a pH sensing test was also performed by using a laboratory-made potentiometer, which showed a sensitivity of 55.4 mV/pH, with the correlation coefficient being greater than 0.99.

Electrochemistry at highly oriented pyrolytic graphite (HOPG): lower limit for the kinetics of outer-sphere redox processes and general implications for electron transfer models.

Abstract: The electron transfer (ET) kinetics of three redox couples in aqueous solution, IrCl6(2-/3-), Ru(NH3)6(3+/2+) and Fe(CN)6(4-/3-), on different grades of highly oriented pyrolytic graphite (HOPG) have been investigated in a droplet-cell setup. This simple configuration allows measurements to be made on a very short time scale after cleavage of HOPG, so as to minimise possible effects from (atmospheric) contamination, and with minimal, if any, change to the HOPG surface. However, the droplet-cell geometry differs from more conventional electrochemical setups and is more prone to ohmic drop effects. The magnitude of ohmic drop is elucidated by modelling the electric field in a typical droplet configuration. These simulations enable ohmic effects to be minimised practically by optimising the positions of the counter and reference electrodes in the droplet, and by using a concentration ratio of electrolyte to redox species that is higher than used conventionally. It is shown that the ET kinetics for all of the redox species studied herein is fast on all grades of HOPG and lower limits for ET rate constants are deduced. For IrCl6(2-/3-) and Fe(CN)6(4-/3-), ET on HOPG is at least as fast as on Pt electrodes, and for Ru(NH3)6(3+/2+) ET kinetics on HOPG is comparable to Pt electrodes. Given the considerable difference in the density of electronic states (DOS) between graphite and metal electrodes, the results tend to suggest that the DOS of the electrode does not play an important role in the ET kinetics of these outer-sphere redox couples over the range of values encompassing HOPG and metals. This can be rationalised because the DOS of all of these different electrode materials is orders of magnitude larger than those of the redox species in solution, so that with strong electronic coupling between the redox couple and electrode (adiabatic electron transfer) the electronic structure of the electrode becomes a relatively unimportant factor in the ET kinetics.

Optimization of electrode characteristics for the Br2/H2 redox flow cell

Abstract: The Br2/H2 redox flow cell shows promise as a high-power, low-cost energy storage device. The effect of various aspects of material selection, processing, and assembly of electrodes on the operation, performance, and efficiency of the system is determined. In particular, (+) electrode thickness, cell compression, hydrogen pressure, and (−) electrode architecture are investigated. Increasing hydrogen pressure and depositing the (−) catalyst layer on the membrane instead of on the carbon paper backing layers have a large positive impact on performance, enabling a limiting current density above 2 A cm−2 and a peak power density of 1.4 W cm−2. Maximum energy efficiency of 79 % is achieved. In addition, the root cause of limiting-current behavior in this system is elucidated, where it is found that Br− reversibly adsorbs at the Pt (−) electrode for potentials exceeding a critical value, and the extent of Br− coverage is potential-dependent. This phenomenon limits maximum cell current density and must be addressed in system modeling and design. These findings are expected to lower system cost and enable higher efficiency.

Hierarchical nanoporous platinum-copper alloy for simultaneous electrochemical determination of ascorbic acid, dopamine, and uric acid

Abstract: A hierarchical nanoporous PtCu alloy was fabricated by two-step dealloying of a PtCuAl precursor alloy followed by annealing. The new alloy possesses interconnected hierarchical network architecture with bimodal distributions of ligaments and pores. It exhibits high electrochemical activity towards the oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA) at working potentials of 0.32, 0.47 and 0.61 V (vs. a mercury sulfate reference electrode), respectively. The new alloy was placed on a glassy carbon electrode and then displayed a wide linear response to AA, DA, and UA in the concentration ranges from 25 to 800 μM, 4 to 20 μM, and 10 to 70 μM, respectively. The lower detection limits are 17.5 μM, 2.8 µM and 5.7 μM at an S/N ratio of 3.