| 1. |
- Alexiadis, Alessio, et al.
(författare)
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Comparison between CFD calculations of the flow in a rotating disk cell and the Cochran/Levich equations
- 2012
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 669, s. 55-66
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Tidskriftsartikel (refereegranskat)abstract
- Three CFD (Computational Fluid Dynamics) models (single-phase. VOF and Euler-Euler) are employed to simulate the flow in a finite, rotating electrode cell under different operative conditions. The main dimensionless groups are derived and their effect on the flow is investigated. Except very close to the rotating electrode (i.e. in the hydrodynamic layer), the results show a flow pattern considerably different from Cochran's approximate analytical solution often used in electrochemistry. Historically, the Cochran equation was used to derive the Levich equation, which permits the calculation of the limiting current density on a rotating electrode. Despite the general inadequacy of Cochran's analytical solution, however, we show that the Levich equation often retains its validity because, in many practical situations, the concentration boundary layer is considerably smaller than the hydrodynamic boundary layer. When bubbles are generated on the electrode and a certain critical void fraction is exceeded, however, the Levich equation also becomes inaccurate. We propose, therefore, an amended version of this equation, which provides results closer to the CFD calculations.
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| 2. |
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| 3. |
- Hussain, Mushtaque, et al.
(författare)
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Effect of anions on the morphology of Co3O4 nanostructures grown by hydrothermal method and their pH sensing application
- 2014
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 717-718, s. 78-82
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Tidskriftsartikel (refereegranskat)abstract
- A fast, reliable, accurate, precise and sensitive pH sensor device is highly demanding for the monitoring of pH in biological, clinical and food industry samples. In this research work, the effect of anions on the morphology of cobalt oxide (Co3O4) nanostructures is investigated using low temperature chemical approach for the growth. Different anions have shown visible effect on the morphology of Co3O4 nanostructures. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy techniques were used for the material characterization. This study has shown highly dense, uniform and good crystal quality of fabricated Co3O4 nanostructures. The nanostructures obtained from the cobalt chloride were used for the development of potentiometric pH sensor electrode. The pH sensor electrode showed excellent linearity and close to Nernstian response for the pH range of 3-13 with a sensitivity of -58.45 mV/pH. Moreover, the proposed sensor showed a fast response time of 53 s, and acceptable reducibility and repeatability. The highly sensitive and a fast time response of the proposed sensor device indicate its potential application for the monitoring of pH from real samples including biological fluids.
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| 4. |
- Jarolimova, Zdenka, et al.
(författare)
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All solid state chronopotentiometric ion-selective electrodes based on ferrocene functionalized PVC
- 2013
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 709, s. 118-125
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Tidskriftsartikel (refereegranskat)abstract
- An all solid contact ion-selective electrode based on poly(vinyl chloride) covalently modified with ferrocene moieties allows one to operate the membrane in a chronopotentiometric sensing mode. The membrane is considered as initially non-perm-selective towards anions, and an applied anodic current provokes a defined anion flux in direction of the membrane. With this protocol, a variety of anions can be depleted at the membrane surface. Since this model system does not yet contain an ionophore, their order of preference follows the expected Hofmeister selectivity sequence. The all solid-state configuration tolerates an imposed current density of 1.4 μA mm−2, which translates into an upper detection limit of ca. 1.2 mM. Higher current densities of up to 31.2 μA mm−2are possible with addition of freely dissolved alkyl ferrocene derivative for an expected upper detection limit of 17.0 mM. Numerical simulations are performed in order to establish the fundamental basis of the mechanism that takes place in this all solid-state membrane electrode. The oxidation of bound Fc and the ion-transfer process are considered in the simulation. In view of developing an analytical sensor, different anions are tested. A linear range of two orders of magnitude from 0.01 to 1 mM is found. The membranes are evaluated over several days, displaying practically the same slopes and intercepts, with a RSD of less than 2%. Electrochemical limitations of free Fc and bound Fc are critical evaluated. This approach should allow one to develop a new family of solid-state chronopotentiometric ion sensors that require relatively high current densities.
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| 5. |
- Karlsson, Christoffer, 1986-, et al.
(författare)
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Quinone Pendant Group Kinetics in Poly(pyrrol-3-ylhydroquinone)
- 2014
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 735, s. 95-98
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we investigate the kinetics of the redox processes occurring in acidic aqueous electrolyte in electropolymerized poly(pyrrol-3-ylhydroquinone), which has been proposed for electrical energy storage applications. The redox conversion of the pendant groups is found to be limited by the quinone redox kinetics in thin films, rather than by the conduction through the polypyrrole backbone. Rate constants for the elementary steps involved in this 2e−, 2H+ process are reported. As the films are made thicker, a gradual transition to a diffusion limited reaction is observed. The origin of the diffusion process, as well as the elementary reaction steps limiting the pendant group redox conversion is analyzed using DFT computations. The fact that the electron transport through the thin film conducting polymer backbone is not limiting the quinone reaction kinetics should allow for design of battery electrodes with high rate capabilities based on the studied material.
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| 6. |
- Nasef, Hany, et al.
(författare)
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Electrochemical molecular beacon DNA biosensor for the detection and discrimination of the DF508 cystic fibrosis mutation
- 2011
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 662:2, s. 322-327
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Tidskriftsartikel (refereegranskat)abstract
- Cystic fibrosis is one of the most common genetically inherited diseases in Northern Europe, consisting of a defect of chloride transport in the epithelium, with the DF508 mutation being the most common mutation associated with the disease. In this work the design and characterisation of a reagent-less electrochemical genosensor, based on the use of an electrochemical molecular beacon targeting the DF508 mutation is presented. Different aspects of the sensing platform including molecular beacon design and surface chemistry of the sensor surface were evaluated. Operational parameters such as assay buffer and assay time were also optimised. Using the optimised molecular beacon designs a clear differentiation between the targeted sequence (i.e. mutant) and potential interferent (i.e. wild type) was demonstrated, with a total required assay time of 20 min. The major advantage of the proposed reagent-less sensing platform is the fact that this only required, as intervention of the end-user, the addition of the sample.
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| 7. |
- Nissfolk, Jarl, et al.
(författare)
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Interpretation of small-modulation photocurrent transients in dye-sensitized solar cells : A film thickness study
- 2010
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 646:1-2, s. 91-99
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Tidskriftsartikel (refereegranskat)abstract
- Electron transport in dye-sensitized solar cells with varying mesoporous TiO2 film thicknesses was investigated using experimental and computational methods. More specifically, photocurrent transients resulting from small-amplitude square-wave modulation of the incident light were recorded for a series of solar cells, whereby the dependence of the wavelength and direction of the illumination was investigated. The responses were compared to simulations using different models for diffusional charge transport and analyzed in detail. The photocurrent transients are composed of two components: an initial fast response in case of illumination from the working electrode side, or an initial apparent delay of photocurrent decay for illumination from the counter electrode side, followed by a single exponential decay at longer times, with a time constant that is identified as the electron transport time. The initial response depends on the thickness and the absorption coefficient of the film. Transport times for different films were compared at equal short-circuit current density, rather than at equal light intensity. Experimentally, the transport time showed a power-law dependence on the film thickness with an exponent of about 1.5. Analysis using the quasi-static multiple trapping (MT) formulation demonstrates that this behavior originates from differences in quasi-Fermi level in the TiO2 films of different thickness when equal photocurrents are generated. The Fokker-Planck relation was used to derive expressions for the electrons flux in porous TiO2 films with a position-dependent diffusion coefficient.
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| 8. |
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| 9. |
- Steegstra, Patrick, 1978, et al.
(författare)
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In situ pH measurements with hydrous iridium oxide in a rotating ring disc configuration
- 2012
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 685, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- Many chemical reactions are pH dependent and for electrochemical reactions taking place at an electrode surface, changes in the near surface pH can be decisive for their outcome. Near surface pH changes have successfully been utilised for formation of oxide films and to control the shape and morphology of the deposit. The mechanistic insight into such processes is hampered by the difficulty to measure the local pH in situ. In the present paper the rotating ring disc electrode (RRDE) configuration is used to measure the near surface pH for two model reactions, hydrogen evolution and oxygen reduction. Iridium oxide is electrodeposited on the titanium ring and used as the pH sensing material. At low current densities and therefore low hydroxide ion concentrations, the pH response is rather slow, limiting the applicability of potentiodynamic sweep experiments under such conditions. At higher current densities a linear relationship between the logarithm of the current and pH is found. Tracking of small pH changes can be made by step experiments where the response is measured as a function of time and steady state conditions can be assured. Key issues for successful use of the RRDE configuration with iridium oxide as the pH sensing material are pre-conditioning of the ring electrode to obtain well defined redox properties of the film and choice of ring substrate onto which the iridium oxide is deposited. (C) 2012 Elsevier B.V. All rights reserved.
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| 10. |
- Tripachev, Oleg, et al.
(författare)
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Gold autodeactivation during oxygen electroreduction studied by electrochemical impedance spectroscopy
- 2012
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 683, s. 21-24
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Tidskriftsartikel (refereegranskat)abstract
- The deactivation of a polycryst. Au electrode is obsd. during O electroredn. reaction (ORR) in basic medium. At that, the cause of the process is chem. decompn. of the ORR intermediate and blocking of active sites of the electrode surface by hydroxyl radical-like species. The deactivation mechanism is discussed.
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