| 1. |
- Larsson, Henrik, et al.
(author)
-
Electron transport in quaternized poly(4-vinylpyridine) films containing pentacyanoferrate(II/III) on electrodes. The influence of the binding type of the electroactive complex
- 1992
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 336:1-2, s. 263-279
-
Journal article (peer-reviewed)abstract
- This study is an attempt to investigate how charge transport in thin redox polymer films spin-coated onto glassy carbon electrode surfaces is affected by the way in which the electroactive group is bound to the polymeric matrix. Two different redox polymers based on methylated and cross-linked poly(4-vinylpyridine) and pentacyanoferrate(II/III) have been synthesized. In the first case, an anionic complex formed by coordinating pyridine to pentacyanoferrate(II) was electrostatically bound to the methylated pyridine groups in the polymer matrix. In the other case, pentacyanoferroate(II) was coordinated directly to unmethylated pyridine groups in the partly methylated polymer film. The film thicknesses were estimated with ellipsometric measurements. Their electrochemical characteristics were investigated using cyclic voltammetry, chronocoulometry and impedance spectroscopy. The apparent charge-transport diffusion coefficient D(app) was almost two orders of magnitude greater in the ion-exchange polymer than in the redox polymer with coordinatively bound electroactive groups. The temperature dependence of D(app) was evaluated using Arrhenius plots.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Eskhult, Jonas, et al.
(author)
-
On the origin of the spontaneous potential oscillations observed during galvanostatic deposition of layers of Cu and Cu2O in alkaline citrate solutions
- 2006
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 594:1, s. 35-49
-
Journal article (peer-reviewed)abstract
- Potential oscillations are demonstrated under reducing galvanostatic conditions in alkaline solutions of 0.4 M Cu(II) and 1.2 M citrate at elevated temperatures. The oscillations, which give rise to the deposition of layers of Cu and Cu2O, as verified by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) as well as Raman measurements, originate from local modulations of the pH in the vicinity of the working electrode. A reaction scheme for the oscillations is presented based on the model previously proposed by Leopold et al. [J. Electroanal. Chem., 547 (2003) 45-52] for the Cu(II)-lactate system. It is shown that the oscillations are due to the fact that the rate of the electrodeposition Of Cu2O is modulated by the local pH variations. This causes this reaction to be switched on and off as the local pH increases and decreases, respectively. In analogy with the Cu(II)-lactate case, a local pH increase is obtained during the deposition of copper from the [Cu(2)H(-2)Cit(2)](4-) complex ([Cu(2)H(-2)Cit(2)](4-) + 4e(-) + 2H(2)O = 2Cu + 2[Cit](3-) + 2OH(-)) predominating in the solution. This increase stems from the protonation of the liberated citrate. As a result of this, electrodeposition Of Cu2O ([Cu(2)H(-2)Cit(2)](4-) + 2e(-) + H2O = Cu2O + 2[Cit](3-)) becomes possible at the rate required by the constant current. However, electrochemical quartz crystal microbalance (EQCM) data clearly show that the onset of this reaction is accompanied by an electroless deposition of Cu2O. This reaction, which under oscillating conditions mainly involves a comproportionation reaction ([Cu(2)H(-2)Cit(2),](4-) + 2Cu + 2OH(-) = 2Cu(2)O + 2[Cit](3-)), can give rise to Cu2O deposition at current efficiencies much larger than 100%. As a result of the combined electroless deposition and electrodeposition Of Cu2O, the local pH decreases rapidly, mainly due to the comproportionation reaction. When the local pH drops, the electrodeposition Of Cu2O becomes unable to sustain the current and the potential shifts negatively. This causes the onset of the reduction of the previously deposited Cu2O (i.e. Cu2O + 2e(-) + H2O = 2Cu + 2OH(-)). The EQCM and XRD results, however, clearly show that this reduction is incomplete during the oscillating conditions. This finding, which explains the presence of both copper and Cu2O in the deposits, is ascribed to the formation of a growing layer of copper on top of the remaining Cu2O. It is shown that the extent of the Cu2O reduction (and thus the amount Of Cu2O in the obtained deposits) depends on the Cu(II) concentration in the solution. Finally, the oscillation cycle is completed by a gradual replacement of the reduction Of Cu2O by the reduction of the [Cu(2)H(-2)Cit(2)](4-) complex, which causes the local pH to increase again. The proposed model is discussed in detail with particular emphasis on the reactions taking place in the region of the oscillation potential peak.The requirements for the attainment of oscillations under quiescent and forced convection conditions are discussed as well as the applicability of the model with respect to other Cu(II)complx systems.
|
|
| 5. |
- Fredin, Kristofer, et al.
(author)
-
The influence of cations on charge accumulation in dye-sensitized solar cell
- 2007
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 609:2, s. 55-60
-
Journal article (peer-reviewed)abstract
- The relation between open-circuit voltage, VOC, light intensity, , and accumulated charge, Q, has been studied for dye-sensitized solar cells (DSCs) containing different counterions to the iodide/triiodide redox couple. At higher light intensities, VOC scaled in the order Cs+ > K+ > Na+ > Li+, which was caused in part by shifts in the conduction band edge. The relation between VOC and Q was fitted to an exponential trap model. It was found that inclusion of a capacitive term improved the fit significantly. The determined values of C were found to be relatively large, up to 75 μF cm−2, and dependent of cation. Physically, the largest fraction of C could be ascribed to the TiO2 bulk or TiO2/dye/electrolyte interface. The interpretation of the trap distribution broadening parameter, β, was found to be dependent of fitting model. Using the model including the linear CVOC term, β was independent of cation and could be viewed as a TiO2 material parameter, while in the model excluding CVOC, β was dependent of cation. Voltage decay experiments were performed to study the cationic influence on recombination. Electron lifetimes were calculated from the voltage decay curves and it was found that the DSC containing Li+ yielded by far the shortest lifetime followed by the DSCs containing Na+, K+ and Cs+. Voltage decay curves include the effect of TiO2 conduction band shifts in the comparison of electron lifetimes with different cations. We therefore suggest that the electron lifetimes should be calculated from the corresponding charge decay curves. From such a comparison, it was found that the DSC containing Li+ yielded the shortest lifetime whereas the DSCs containing Na+, K+ or Cs+ showed approximately identical lifetimes.
|
|
| 6. |
- Jarolimova, Zdenka, et al.
(author)
-
All solid state chronopotentiometric ion-selective electrodes based on ferrocene functionalized PVC
- 2013
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 709, s. 118-125
-
Journal article (peer-reviewed)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.
|
|
| 7. |
- Karlsson, Christoffer, 1986-, et al.
(author)
-
Quinone Pendant Group Kinetics in Poly(pyrrol-3-ylhydroquinone)
- 2014
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 735, s. 95-98
-
Journal article (peer-reviewed)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.
|
|
| 8. |
- Lindberg, Jonas, et al.
(author)
-
The effect of O2 concentration on the reaction mechanism in Li-O2 batteries
- 2017
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728 .- 1873-2569. ; 797, s. 1-7
-
Journal article (peer-reviewed)abstract
- The promising lithium-oxygen battery chemistry presents a set of challenges that need to be solved if commercialization is ever to be realized. This study focuses on how the O2 reaction path is effected by the O2 concentration in the electrolyte. An electrochemical quartz crystal microbalance system was used to measure current, potential, and change in electrode mass simultaneously. It is concluded that the mass reversibility is O2 concentration dependent while the coulombic efficiency is not. The mass reversibility is higher at low O2 concentration meaning that more of the deposited Li2O2 is removed during oxidation in relation to the amount deposited during reduction. The first step of the reduction is the formation of soluble LiO2, which is then either reacting further at the electrode or being transported away from the electrode resulting in low current efficiency and low deposited mass per electrons transferred. During the oxidation, the first step involves de-lithiation of Li2O2 at low potential followed by bulk oxidation. The oxidation behavior is O2 concentration dependent, and this dependence is likely indirect as the O2 concentration effects the amount of discharge product formed during the reduction. The O2 concentration at different saturation pressures was determined using a mass spectrometer. It was found that the electrolyte follows Henry's law at the pressures used in the study. In conclusion, this study provides insight to the O2 concentration dependence and the preferred path of the O2 electrochemical reactions in lithium-oxygen batteries.
|
|
| 9. |
- Nasef, Hany, et al.
(author)
-
Electrochemical molecular beacon DNA biosensor for the detection and discrimination of the DF508 cystic fibrosis mutation
- 2011
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 662:2, s. 322-327
-
Journal article (peer-reviewed)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.
|
|
| 10. |
- Paulsson, Heléne, et al.
(author)
-
Electron transport and recombination in dye-sensitized solar cells with ionic liquid electrolytes
- 2006
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 586:1, s. 56-61
-
Journal article (peer-reviewed)abstract
- The electron transport and recombination in dye-sensitized TiO2 solar cells with different electrolytes have been investigated. The electrolytes were based on iodine-doped ionic liquids (diethylmethylsulphonium, dibutylmethylsulphonium or 3-hexyl-1-methylimidazolium iodide) or an organic solvent (3-methoxypropionitrile with LiI, I-2 and 1-methylbenzimidazole). The most viscous electrolytes showed a clear limitation in photocurrent, which can be attributed to a low diffusion coefficient for the triiodide that transports positive charge to the counter electrode. No essential difference was found in the electron transport properties of the solar cells, which appear to be dominated by the properties of the nanostructured TiO2 film. The intensity-modulated photocurrent response was strongly affected by current saturation. This is proposed being caused by recombination processes. The electron lifetime is depending on the type of cation used in the ionic liquid, where bulky, less absorptive cations seem to give longer lifetimes.
|
|
| 11. |
- Ruiz, Vanesa, et al.
(author)
-
A study of Faradaic phenomena in activated carbon by means of macroelectrodes and single particle electrodes
- 2008
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 618:1-2, s. 33-38
-
Journal article (peer-reviewed)abstract
- The electrochemical behaviour of a chemically activated carbon with oxygen-containing surface groups was studied using a conventional macroelectrode configuration with disc electrodes and the single particle microelectrode technique. The results of both experimental set-ups were compare taking into account the visible peaks of the surface groups, capacitance and Faradaic currents. Galvanostatic cycling and cyclic voltammetry performed at different potential windows clearly indicated that the microelectrode configuration was more sensitive to Faradic phenomena (i.e. oxygenated functional groups). The incorporation of mainly CO2-evolving groups after positive polarization may cause the degradation of the carbon material, leading to a distortion in its capacitive behaviour as a result of a restriction of the available surface area.
|
|
| 12. |
- Sjödin, Martin, 1974-, et al.
(author)
-
Proton-coupled electron transfer from an interfacial phenol monolayer
- 2020
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 859
-
Journal article (peer-reviewed)abstract
- A tert-butyl protected phenol is covalently link to a mixed self-assembled monolayer on a gold or platinum electrode. The phenol reduction potential shows the expected pH-dependence of a one-electron, one-proton couple with a decrease in formal reduction potential of 59 ± 5 mV per pH. A titration of the phenol is observed with a pKa of 13.2 and the reduction potential for the phenolate is 0.11 V . NHE. The kinetic behavior of the proton-coupled oxidation deviates substantially from the commonly used models for a step-wise reaction that assume the proton transfer reactions are in equilibrium throughout the reaction. A novel model for step-wise proton-coupled reactions is presented that fully accounts for the pH dependent kinetics and allows the formal rate constants and the transfer coefficients to be determined.
|
|
| 13. |
- Sjödin, Martin, 1974-, et al.
(author)
-
Reprint of "Proton-coupled electron transfer from an interfacial phenol monolayer"
- 2020
-
In: Journal of Electroanalytical Chemistry. - : ELSEVIER SCIENCE SA. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 875
-
Journal article (peer-reviewed)abstract
- A tert-butyl protected phenol is covalently link to a mixed self-assembled monolayer on a gold or platinum electrode. The phenol reduction potential shows the expected pH-dependence of a one-electron, one-proton couple with a decrease in formal reduction potential of 59 +/- 5 mV per pH. A titration of the phenol is observed with a pK(a) of 13.2 and the reduction potential for the phenolate is 0.11 V. NHE. The kinetic behavior of the proton-coupled oxidation deviates substantially from the commonly used models for a step-wise reaction that assume the proton transfer reactions are in equilibrium throughout the reaction. A novel model for step-wise proton-coupled reactions is presented that fully accounts for the pH dependent kinetics and allows the formal rate constants and the transfer coefficients to be determined.
|
|
| 14. |
- Tripachev, Oleg, et al.
(author)
-
Gold autodeactivation during oxygen electroreduction studied by electrochemical impedance spectroscopy
- 2012
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 683, s. 21-24
-
Journal article (peer-reviewed)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.
|
|
| 15. |
- Waita, Sebastian M., et al.
(author)
-
Electrochemical Characterization of TiO2 Blocking Layers Prepared by Reactive DC Magnetron Sputtering
- 2009
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 637:1-2, s. 79-83
-
Journal article (peer-reviewed)abstract
- Thin TiO2 (anatase) films were prepared by reactive DC magnetron sputtering and characterized in detail. Specifically, they were tested as compact blocking underlayers in dye-sensitized solar cells. Elastic recoil detection analysis and optical measurement showed some porosity in the sputtered films, but electrochemical measurements demonstrated good blocking characteristics. This suggests the presence of small voids rather than pinholes in the deposited films. In the case of an iodide/iodine redox couple, thin underlayers (similar to 20 nm) improved the fill factor without affecting other properties of the cell. in case of a ferrocene/ferrocenium-based electrolyte, the presence of underlayers was necessary to obtain functional dye-sensitized solar cells.
|
|
| 16. |
- Waita, Sebastian M., et al.
(author)
-
Electron transport and recombination in dye sensitized solar cells fabricated from obliquely sputter deposited and thermally annealed TiO2 films
- 2007
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728 .- 1873-2569. ; 605:2, s. 151-156
-
Journal article (peer-reviewed)abstract
- Dye sensitized solar cells based on annealed titanium dioxide films prepared by oblique reactive DC magnetron sputtering have been investigated in detail. Electron transport and recombination were studied using intensity-modulated photocurrent and photovoltage spectroscopy. Electron transport time as well as lifetime were found to increase upon lowering of the light intensity and to increase upon increasing the thickness of the TiO2 film. The properties are very similar to those observed for solar cells based on colloidal TiO2 films despite the morphologies being very different. In all cases, films are composed of a porous assembly of TiO2 nanocrystals. Grain boundaries with associated trap and/or energy barriers may explain the observed transport properties.
|
|
| 17. |
- Zettersten, Camilla, et al.
(author)
-
The influence of the thin-layer flow cell design on the mass spectra when coupling electrochemistry to electrospray ionisation mass spectrometry
- 2006
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 590:1, s. 90-99
-
Journal article (peer-reviewed)abstract
- The influence of the flow cell configuration on the mass spectra obtained when coupling an electrochemical thin-layer flow cell to electrospray mass spectrometry (ESI-MS) has been investigated. It is shown that interferences due to the electrochemical reaction on the counter electrode and/or the absence of 100% conversion efficiency can alter the mass spectra when conventional thin-layer flow cells are used in conjunction with ESI-MS. The effects, which affect the intensities and distribution of the peaks in the mass spectra, can result in the inability to detect products formed at the working electrode. Comparisons of mass spectra, generated after the electrochemical oxidation of a dinuclear Mn complex (where bpmp = 2,6-bis[bis(2-pyridylmethyl) amino]methyl-4-methylphenol) using two different thin-layer flow cells clearly show that the potential dependence and appearance of the mass spectra depend on the flow cell configuration used. The use of a modified thin-layer flow cell, in which the counter electrode had been separated from the working electrode, gave rise to significantly increased intensities for the oxidised MnIII,IV state of the complex. With the conventional unmodified cell, the corresponding complex was only seen for considerably higher oxidation potentials. The different results can be explained by the reduced risk of redox cycling and interferences due to species generated at the counter electrode with the modified cell. As interferences due to the counter electrode reactions likewise may be expected with many coulometric flow cells, the electrochemical cell design clearly needs to be considered when using electrochemistry coupled to ESI-MS to study electrochemical reactions.
|
|
| 18. |
- Zuleta, Marcelo, et al.
(author)
-
Determination of diffusion coefficients of BF4- inside carbon nanopores using the single particle microelectrode technique
- 2006
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 586:2, s. 247-259
-
Journal article (peer-reviewed)abstract
- The electrochemical and mass transport properties of TEABF(4) in a nanoporous (NP) carbon material, obtained from silicon carbide, was studied using single particles and a microelectrode technique. The carbon particles of size 100-200 mu m were studied by cyclic voltammetry and potential step measurements. The effective diffusion coefficients (D-eff) were calculated starting from the asymptotic solutions of Fick's second law for short and long time regions. The results show that cycling at low sweep rates was needed in order for the electrolyte to penetrate the inner porosity of the particles. The carbon material showed different electrochemical and mass transport properties depending on the applied potential. At negative polarisation, the results suggest that TEA(+) was adsorbed on the pore wall, however, being transported very slowly inside the pores. The average D-eff after cycling at both positive and negative potentials was 1.1(+/- 0.4) x 10(-8) cm(2) s(-1), using the Cottrell relation and 1.5(+/- 0.6) x 10(-8) cm(2) s(-1), using the radial diffusion solution. The average value of D-eff after cycling at negative potentials was 1.7(+/- 0.6) x 10(-8) cm(2) s(-1) using both mathematical solutions.
|
|
| 19. |
- Zyoud, Ahed, et al.
(author)
-
Combined electrochemical/chemical bath depositions to prepare CdS film electrodes with enhanced PEC characteristics
- 2013
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 707, s. 117-121
-
Journal article (peer-reviewed)abstract
- A new method to prepare CdS film electrodes, based on electrochemical deposition (ECD), followed by chemical bath deposition (CBD), is described. The ECD/CBD-CdS film electrodes combine the advantages of both ECD-CdS film (good adherence to FTO/glass substrate) and CBD-CdS film (suitable film thickness) together. The new ECD/CBD electrode showed higher photo-electrochemical (PEC) efficiency and stability than either ECD- or CBD-CdS film electrodes, especially after annealing. Inter-particle connection and uniformity of the ECD/CBD-CdS film were further enhanced by annealing. Consequently, the electrode PEC conversion efficiency and stability were enhanced. The combined preparation technique, followed by annealing, is potentially useful for future manufacturing of CdS and other film electrode systems. (C) 2013 Elsevier B.V. All rights reserved.
|
|
| 20. |
- Fontes, Eduardo, et al.
(author)
-
Mathematical modelling of the MCFC cathode : On the linear polarisation of the NiO cathode
- 1997
-
In: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 432:1-2, s. 121-128
-
Journal article (peer-reviewed)abstract
- Experimental polarisation curves for the porous lithiated NiO cathode used in molten carbonate fuel cells very often exhibit a linear shape over a wide potential range. It is shown by means of mathematical modelling that this linear behaviour can be explained by the interplay of intrinsic electrode kinetics, diffusion of electroactive species through an electrolyte film and the effective ohmic resistance of the pore electrolyte, providing that the cathodic transfer coefficient has a value of about 1.5. In contrast, with the generally assumed value of 0.5 of this transfer coefficient and with reasonable values of the effective electrolyte conductivity, predicted polarisation curves will always bend downwards over the overvoltage region of interest. The evolution of the polarisation curves with increasing electrolyte fill can be simulated by a model according to which the electroactive surface area becomes gradually blocked with the increasing amount of electrolyte.
|
|
| 21. |
- Gode, Peter, et al.
(author)
-
In-situ measurements of gas permeability in fuel cell membranes using a cylindrical microelectrode
- 2002
-
In: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 518:2, s. 115-122
-
Journal article (peer-reviewed)abstract
- A new method to study permeation of gases in proton conducting membranes using a cylindrical microelectrode is presented. The focus of this work was to develop an in-situ method to study transport properties of hydrogen and oxygen close to real fuel cell operating conditions. The gas permeability is strongly affected by the change of water content in the membrane and it is therefore of advantage that, by using this method, measurements can be carried out over a wide range of relative humidities. The numerical method makes it possible to separate the diffusion coefficient and the concentration of dissolved gas in the membrane and also allows kinetic limitations to be taken into account. Chronoamperometric measurements on Nafion(R) 117 were successfully evaluated numerically. Experiments at temperatures of 25 and 60 degreesC with respect to oxygen permeation and at 60 degreesC for hydrogen permeation at relative humidities in the range 30-94% are presented. The reproducibility of data was excellent when measuring with different microelectrodes, on the same membrane sample, but differed when measuring on different samples. In general, the permeability increases with increasing temperature and relative humidity.
|
|
| 22. |
- Hjelm, A. K., et al.
(author)
-
Investigation of LiMn2O4 cathodes for use in rechargeable lithium batteries by linear sweep voltammetry (LSV) Part II. Experimental study using thin films, single particles and composite electrodes
- 2001
-
In: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 509:2, s. 139-147
-
Journal article (peer-reviewed)abstract
- Thin films, single particles and a composite electrode of the cathode material LiMn2O4 in the lithium battery system were investigated by linear sweep voltammetry (LSV) in 1 M LiClO4 + PC:EC. The experimental data were compared to and analysed by mathematical models described in Part I of this work. Analysis of the measured peak potential. E-p, showed clearly that the larger the characteristic length, the larger is the potential peak shift., at a given sweep rate. From the observations of the measured peak current behaviour, I-p, it seems that the composite electrode and the single particles are semi-infinite diffusion limited at all sweep rates applied. For the thin films, when increasing the sweep rate, a transition from finite to semi-infinite mass transfer limitation is indicated. A model based on solid-phase diffusion, interfacial charge transfer and an external IR-drop could fairly well be fitted to the experimental data measured on a single electrode system at a given sweep rate. It was found that the determined parameter values. i.e. solid-phase diffusion coefficient and the IR-drop, vary greatly with sweep rate and characteristic length. These results indicate that the physical description used is an oversimplification for describing the reaction mechanism in LiMn2O4.
|
|
| 23. |
- Hjelm, A. K., et al.
(author)
-
Investigation of LiMn2O4 cathodes for use in rechargeable lithium batteries by linear sweep voltammetry Part I. Theoretical study
- 2001
-
In: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 506:2, s. 82-91
-
Journal article (peer-reviewed)abstract
- Linear sweep voltammetry (LSV) is a well-known tool for electrochemical investigations. Different aspects on the use of LSV in the study of an intercalation electrode in the rechargeable lithium battery system have been studied. Mathematical models were used to simulate voltammetry responses for an intercalation material influenced by solid phase diffusion, charge transfer and IR-drop. It was shown how the peak potential and the peak current density vary with sweep rate for different rate determining processes. The simulations show that finite and semi-infinite diffusion is relatively easy to distinguish and also, these two processes behave differently from processes influenced by charge transfer and an external IR-drop. However, the separation of charge transfer and IR-drop is difficult. The use of the convolution sweep voltammetry method was also investigated. It was found that finite diffusion and a non-zero initial concentration limit the applicability in these systems.
|
|
| 24. |
- Kostela, Johan, 1975-, et al.
(author)
-
Electrochemical properties of an amphiphilic viologen in differently charged micelles
- 2002
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569. ; 536:1-2, s. 97-107
-
Journal article (peer-reviewed)abstract
- The electrochemical properties of N-tetradecyl-N′-methylviologen (TMV) in differently charged micelles were studied with a glassy carbon electrode using electrochemical techniques. The redox potential varied depending on the charge of the surrounding surfactants. When the viologen was situated in cationic micelles the redox potential for the 2+/1+ reaction was more positive than when situated in negatively charged micelles. The non-ionic micelles destabilised the 2+-state most showing the highest redox potentials. From studies of several different cationic micelles it was concluded that the most important parameter for the redox potential was the surface charge density. A calculation based on a simple model confirmed this. Other interactions also influenced the stability of the redox states. Adsorption, desorption and reorganisation of the surfactants at the electrode surface caused capacitive currents. To control the nonfaradaic current, differential pulse voltammetry (DPV) was used in addition to cyclic voltammetry.
|
|
| 25. |
- Larsson, Henrik, et al.
(author)
-
Charge propagation in [Os(bpy)2(PVP)xCl]Cl polymers. An example of mean field behavior in a system with constrained diffusion of redox sites?
- 1995
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569. ; 381:1-2, s. 133-142
-
Journal article (peer-reviewed)abstract
- Chronocoulometry and impedance spectroscopy were used to study the dynamics of charge transport in a series of methylated [Os(bpy)(2)(PVP)(x)Cl]Cl polymers (PVP = poly(4-vinylpyridine); bpy = 2,2'-bipyridine; 5 less than or equal to x less than or equal to 40) which were deposited as thin firms on glassy carbon electrodes. Apparent charge propagation diffusion coefficients D-app were of the order of 10(-8) cm(2) s(-1) and were approximately linearly dependent on the total concentration of redox sites but independent of the ratio of oxidized to reduced centres present in a particular coating. Attempts were made to explain these observations in terms of a recent theory of charge transport appropriate for systems in which the redox sites are permanently attached to the polymer chains. It was found that the concentration dependence and magnitude of D-app could be explained satisfactorily by a mean field model of charge propagation.
|
|
| 26. |
- Sharp, Michael, et al.
(author)
-
Studies of the temperature dependence of charge propagation rates in quaternized poly(4-vinylpyridine) polymers containing electrostatically bound and coordinated redox sites
- 1995
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569. ; 386:1-2, s. 189-195
-
Journal article (peer-reviewed)abstract
- The activation parameters associated with charge propagation in a series of quaternized poly(4-vinylpyridine) polymers, which contained both electrostatically hound and coordinated redox sites and which were deposited as thin films on electrode surfaces, were derived from the temperature dependence of apparent charge transport diffusion coefficients. The values of the activation energies and entropies obtained are discussed in terms of models of charge transport that are appropriate for redox polymers in which physical displacements of the redox sites are either free or constrained.
|
|
| 27. |
- Yang, Zhongping, et al.
(author)
-
Electrochemical characterisation of mixed monolayer assemblies of thiol analogues of cholesterol and fatty acids on gold
- 1997
-
In: Journal of Electroanalytical Chemistry. - : Elsevier Science B.V., Amsterdam.. - 0022-0728 .- 1873-2569. ; 430:1-2, s. 189-195
-
Journal article (peer-reviewed)abstract
- A self-assembled monolayer (SAM) on gold prepared from a binary mixture of a thiol analogue of cholesterol (thiocholesterol, TC) and a functionalised alkanethiol (11-mercaptoundecanoic acid, MUA) has been investigated by voltammetry. The voltammetric results are in agreement with previously reported spectroscopic data and show that the geometric arrangement and composition of the molecules in the mixed monolayer controls the heterogeneous electron transfer process of Fe(CN)(6)(3-) across the assembly. The quantitative description of the influence of TC on the electron transfer rate constant is given through Tafel plots. At the pure MUA SAM electrode, the electron transfer is governed by penetration through the monolayer. The introduction of TC into the SAMs creates defects giving rise to diffusion controlled electron transfer in addition to penetration. By raising the TC content the electron transfer rate constant increases due to diffusion, This behaviour can be explained by a model in which the assembly goes from a penetrative but defect-free film barrier (pure MUA SAM) via a structure with defects in the mixed composition regime to a defect-rich structure consisting of an array of ultramicroelectrodes (pure TC SAM). (C) 1997 Elsevier Science S.A.
|
|
| 28. |
- Zuleta, Marcelo, et al.
(author)
-
Determination of the effective diffusion coefficient of nanoporous carbon by means of a single particle microelectrode technique
- 2003
-
In: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 549, s. 101-108
-
Journal article (peer-reviewed)abstract
- A single particle microelectrode technique with a micromanipulator was applied and adapted for characterisation of mass transport properties of ionic species in a high surface area nanoporous carbon, with uniform pore size of 8 Angstrom. The effective diffusivity of 6 M KOH in this material was determined by means of potential step experiments on nanoporous carbon particles of different sizes. The results were analysed for short times (Cottrell model) and for long times (spherical diffusion model). The average effective diffusion coefficient for short and long times was 1.5x10(-9) and 1.2x10(-9) cm(2) s(-1), respectively. The relatively small diffusivity values are discussed in terms of interaction between the ion hydration shell and water molecules adsorbed on the pore wall.
|
|
| 29. |
- Böhme, Solveig, 1987-, et al.
(author)
-
Overlapping and rate controlling electrochemical reactions for tin(IV) oxide electrodes in lithiu-ion batteries
- 2017
-
In: Journal of Electroanalytical Chemistry. - 0022-0728 .- 1873-2569. ; 797, s. 47-60
-
Journal article (peer-reviewed)abstract
- The results of this extensive electrochemical study of the electrochemical reactions of SnO2 electrodes in lithium-ion batteries demonstrate that the different reduction and oxidation reactions overlap significantly during the cycling and that the rates of the redox reactions are limited by the mass transport through the layers of oxidation or reduction products formed on the electrodes. The experiments, which were carried out in the absence and presence of the lithium alloy reactions, show that the capacity losses seen on the first cycles mainly can be explained by an incomplete oxidation of the lithium tin alloy and an incomplete reformation of SnO2. The latter can be explained by the formation of thin tin oxide layers (i.e., SnO and SnO2), protecting the remaining tin, as the oxidation current then becomes limited by the Li+ diffusion rate though these layers. The results, also show that the first cycle SnO2 reduction was incomplete for the about 20 μm thick electrodes containing 1 to 6 μm large SnO2 particles. This can be ascribed to the formation of a layer of tin and Li2O (protecting the remaining SnO2) during the reduction process. Although the regeneration of the SnO2 always was slower than the reduction of the SnO2, the results clearly show that the SnO2 conversion reaction is far from irreversible, particularly at low scan rates and increased temperatures. Electrochemical cycling at 60 °C hence gave rise to increased capacities, but also a faster capacity loss, compared to at room temperature. These new findings indicate that a full utilization of SnO2 based electrodes at a given cycling rate only can be reached with sufficiently small particles since the allowed particle size is given by the time available for the mass transport through the formed surface layers. The present results consequently provide important insights into the phenomena limiting the use of SnO2 electrodes in lithium-ion batteries.
|
|
| 30. |
|
|
| 31. |
- Hussain, Mushtaque, et al.
(author)
-
Effect of anions on the morphology of Co3O4 nanostructures grown by hydrothermal method and their pH sensing application
- 2014
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 717-718, s. 78-82
-
Journal article (peer-reviewed)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.
|
|
| 32. |
|
|
| 33. |
|
|
| 34. |
- Larses, Patrik, et al.
(author)
-
Hydrogen evolution at mixed α-Fe1 − xCrxOOH
- 2018
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728. ; 819, s. 114-122
-
Journal article (peer-reviewed)abstract
- The activity of mixed α-Fe 1 − x Cr x OOH oxides towards hydrogen evolution in alkaline solution is discussed based on Density Functional Theory (DFT) calculations, cyclic voltammetry and steady state measurements. Thermogravimetric and XRD measurements indicate an isomorphic substitution of Fe by Cr. Electrochemical characterization shows increasingly sluggish hydrogen evolution reaction (HER) kinetics with increased Cr loadings. This decrease in activity is accompanied by the inhibition of the reduction of iron in α-Fe 1 − x Cr x OOH. To investigate the origin of this decrease in activity, DFT calculations were performed for mixtures of Fe and Cr placed at Fe(OH) 2 . Based on phase diagrams, the most stable structures under HER conditions are identified and used to estimate the theoretical overpotential. In contrast to experiment, no decrease in HER activity is observed. Instead, mixed FeCr sites display an overpotential comparable to that of Pt. Taking into account the inhibition of the bulk reduction in the presence of Cr, the activity decreases in agreement with experiment. These results are very important in the search for cathodes in the chlorate process that are active also in the absence of chromate in solution and may offer a new route for Pt free HER catalysts in alkaline solution.
|
|
| 35. |
- Larsson, Henrik
(author)
-
Ellipsometric determinations of the thicknesses of dry and electrolyte-immersed poly(4-vinylpyridine) films containing coordinated light-absorbing [Os(bpy)2pvpCl]2+/+ redox groups
- 1994
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 365:1-2, s. 229-237
-
Journal article (peer-reviewed)abstract
- Ellipsometry has been used to measure the dimensions of quaternized poly(4-vinylpyridine) films containing [Os(bpy)2pvpCl]2+/+ redox groups on glassy carbon electrodes. Film thicknesses and complex refractive indices were deduced using molar absorptivities obtained from photometry or a combination of photometry and cyclic voltammetry. The precision in the film thicknesses was estimated using data obtained from thick and thin films with the same polymer + redox group compositions and from data recorded at 60-degrees and 70-degrees angles of incidence of 633 nm laser light. The effects of errors in the experimentally determined molar absorptivity of the redox groups on film thickness were also assessed. The results of this study suggest that reliable thicknesses can be obtained for both dry and electrolyte-swollen films, and that the presence of light-absorbing redox groups within coatings such as these presents no real obstacle for ellipsometric determinations.
|
|
| 36. |
|
|
| 37. |
- Phal, Sereilakhena, et al.
(author)
-
Covalently electrografted carboxyphenyl layers onto gold surface serving as a platform for the construction of an immunosensor for detection of methotrexate
- 2018
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 812, s. 235-243
-
Journal article (peer-reviewed)abstract
- Abstract The classical way to modify a gold electrode surface for immunosensor development is through self-assembly of functionalised thiols for subsequent attachment of antibodies. Here is described a new pathway for surface modification using a diazonium salt-based immunosensor for detection of methotrexate (MTX) with electrochemical immittance spectroscopy (EIS). The diazonium salt, 4-carboxybenzenediazonium tetrafluoroborate was synthesized using a diazotization reaction and characterized by IR and cyclic voltammetry (CV). The Au electrode was electrografted with diazonium and used for anti-MTX antibody immobilization. The EIS detection of MTX was studied with and without application of redox probe; Fe(CN)63−/4−. MTX could not be detected using Fe(CN)63−/4−as redox probe, whereas EIS measurements without redox probe and analysis of the data with singular decomposition (SVD) gave good results. A multivariate calibration model showed good linear behavior on a logarithmic scale with a detection limit for MTX of 7×10−12molL−1.
|
|
| 38. |
|
|
| 39. |
- Wreland Lindström, Rakel, et al.
(author)
-
Electrocatalysis and transport effects on nanostructured Pt/GC electrodes
- 2010
-
In: J ELECTROANAL CHEM. - : Elsevier BV. - 1572-6657 .- 0022-0728. ; 644:2, s. 90-102
-
Journal article (peer-reviewed)abstract
- The role and contribution of transport processes in electrocatalytic reactions was investigated in model studies of the oxidation of CO (single-product reaction) and formaldehyde (dual-product reaction), using nanostructured Pt/glassy carbon electrodes with variable Pt loading and defined reactant transport conditions. Nanostructured electrodes with monodispersed, uniformly distributed Pt nanostructures (100-140 nm diameter) supported on planar glassy carbon (GC) electrodes with different densities were prepared by Colloidal Lithography (CL) or Hole-Mask Colloidal Lithography (HCL). Transport effects were evaluated by varying the density of the nanostructures and the electrolyte flow. The resulting changes in the transport limited reaction current (CO oxidation - transition from planar to spherical diffusion with decreasing Pt nanostructure density) and in the distribution of the reaction products HCOOH and CO2 (HCHO oxidation), which is probed by differential electrochemical mass spectrometry (DEMS), are discussed focusing on transport effects. The increasing amount of CO2 with decreasing space velocity (higher nanostructure density, lower electrolyte flow) is explained by increasing re-adsorption and further reaction of desorbing reaction intermediates. (C) 2009 Elsevier B.V. All rights reserved.
|
|
| 40. |
- Alexiadis, Alessio, et al.
(author)
-
Comparison between CFD calculations of the flow in a rotating disk cell and the Cochran/Levich equations
- 2012
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 669, s. 55-66
-
Journal article (peer-reviewed)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.
|
|
| 41. |
- Castillo, John, et al.
(author)
-
Direct electrochemistry and biolelectrocatalysis of H2O2 reduction of recombinant tobacco peroxidase on graphite. Effect of peroxidase single-point mutation on Ca2+-modulated catalytic activity
- 2006
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 588:1, s. 112-121
-
Journal article (peer-reviewed)abstract
- Direct electron transfer (DET) reactions and bio(electro)catalytic reduction of H2O2 catalysed by native and recombinant forms of tobacco peroxidase (nTOP and rTOP) were studied in homogeneous-phase catalysis and when TOPs were adsorbed on graphite electrodes. Non-glycosylated wild type and Glu141 -> Phe mutant forms of rTOP were produced using an Escherichia coli expression system. Mutation was introduced to explore the mechanisms for modulation of the catalytic activity of TOP by Ca2+ ions. At the pH optimum of 5.0, direct electrochemical Fe3+/2+ transformation of the peroxidase heme was characterised by potentials of -208 mV (nTOP) and -239 mV vs. Ag vertical bar AgCl (rTOP), and 0.9 +/- 0.1 and 1.1 +/- 0.4 pmoles of adsorbed nTOP and rTOP, correspondingly, were in DET contact with graphite. Kinetic analysis of amperometric (at +50 mV) data on H2O2 reduction at TOP-modified electrodes, placed in a wall-jet flow-through electrochemical cell, yielded 82% (nTOP) and 88% (rTOP) of adsorbed TOP molecules active in the DET reaction. The efficiency of DET (and bioelectrocatalysis) increased 3.5-fold when changing from glycosylated nTOP to rTOP. The Glu141 Phe mutation in the heme-binding pocket of rTOP enabled to achieve a Ca2+-tolerance of TOP in the reaction with H2O2, which is characteristic of other plant peroxidases, and to a large extent in heterogeneous DET and reaction with a second substrate catechol. The results promote further applications of TOP for biosensor- and solid-phase biocatalysts development. (c) 2005 Elsevier B.V. All rights reserved.
|
|
| 42. |
- Evertsson, Jonas, et al.
(author)
-
Anodization of Al(100), Al(111) and Al Alloy 6063 studied in situ with X-ray reflectivity and electrochemical impedance spectroscopy
- 2017
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 799, s. 556-562
-
Journal article (peer-reviewed)abstract
- We present results from the anodization of single crystal Al(100) and Al(111) surfaces and the aluminum alloy AA 6063 studied in situ by X-ray reflectivity and electrochemical impedance spectroscopy. We observe that the anodic oxide layer grows linearly with the anodization potential and that the thicknesses are similar for all samples. However, the thicknesses obtained from X-ray reflectivity are higher than that obtained from electrochemical impedance spectroscopy. We attribute the higher thicknesses to an outer porous oxide layer, which is not detected by electrochemical impedance spectroscopy. Both, electrochemical impedance spectroscopy and X-ray reflectivity suggests that a more heterogeneous and rough oxide is formed on AA 6063 due to the influence of the alloying elements and intermetallic particles during the growth.
|
|
| 43. |
- Gonzalez-Arribas, Elena, et al.
(author)
-
A conventional symmetric biosupercapacitor based on rusticyanin modified gold electrodes
- 2018
-
In: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657. ; 816, s. 253-258
-
Journal article (peer-reviewed)abstract
- Here we report on an entirely new kind of bioelectronic device - a conventional biosupercapacitor, which is built from copper containing redox proteins. Prior to biodevice fabrication, detailed spectroelectrochemical studies of the protein, viz. Acidithiobacillus ferrooxidcats rusticyanin, in solution and in adsorbed state, were performed, including estimation of the redox potential of the T1 site (0.62 V vs. NHE), protein midpoint potential when adsorbed on a self-assembled monolayer (0.34 V vs. NHE), as well as biocapacitance of rusticyanin modified gold electrodes (115 mu F cm(-2)). The symmetrical biosupercapacitor based on two identical gold electrodes modified with rusticyanin is able to capacitively store electricity and deliver electric power accumulated mostly in the form of biopseudocapacitance, when charged and discharged externally. When charged during Just 5 s, the biosupercapacitor with a total capacitance of about 73 mu F cm(-2) provided a maximum of 4 mu A cm(-2) peak current at 0.40 V. The biodevice, which can be charged and discharged at least 50 times without a significant loss of ability to store electric energy, had a low leakage current below 50 nA cm(-2).
|
|
| 44. |
|
|
| 45. |
- Hadidi, Hooman, et al.
(author)
-
Numerical investigation of capacitive deionization (CDI) with divergent and convergent channels
- 2023
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 944
-
Journal article (peer-reviewed)abstract
- This research aims to explore the impact of tilted channel configurations of CDI cells on desalination performance. The results reveal that the titled convergent channels have a faster average salt adsorption rate (ASAR) than the regular straight geometry. For desalination operations that end at a quarter of the equilibrium salt adsorption capacity (SAC), the convergent spacer with a slight slope of 1.5 degrees has a 20 % higher ASAR than the typical straight geometry (0.15 mg/g/min for convergent and 0.12 mg/g/min for straight). This gain increases to about 24, 29.5, and 33%, respectively, for slopes of 3.5, 5.5, and 7 degrees, compared to the straight geometry with the same spacer thickness. By looking at the underlying mechanisms, the spacer geometry is found to shift the location of the initial adsorption. This affects how quickly the device outputs the cleaned water. Interestingly, the geometry angle can also affect the location of the depletion zone, so tilted spacers can also affect the behavior during electrode starvation. Specifically, the convergent geometry has the depletion zone in the middle of the electrode instead of the corner near the outlet, as seen for straight and divergent channels. Together, these findings indicate how to construct tilted spacers to enhance CDI performance.
|
|
| 46. |
|
|
| 47. |
|
|
| 48. |
- Johnsson Wass, J R Tobias, et al.
(author)
-
Quantum chemical modelling of oxygen reduction on cobalt hydroxide and oxyhydroxide
- 2007
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 599:2, s. 295-312
-
Journal article (peer-reviewed)abstract
- Quantum chemistry has been employed to analyse the experimentally observed production of H2O2 during electrochemical reduction of O-2 on cobalt oxyhydroxide, CoOOH(s). The site for O-2 reduction was modelled using both small hydrated Co hydroxide clusters and periodic slab models of a step edge site. A catalytic site was found for the Co(II) model cluster, Co(OH)(2)(H2O)(7), which was also found in the step edge models. However, the site was found to bind O-3(2) very loosely and the Co(II) site alone displayed no electron affinity. The reduction reaction was initiated by adding an electron with O-2 present at the Co(II) site. This produces a superoxide ligand, which upon protonation is able to undergo further reduction to HO2- as Co(III) is formed at the site. Adding a second electron leads to detachment of HO2- as Co(II) is restored. A catalytic redox cycle is presented based on this understanding. The reduction behaviour explains why O-2 is readily reduced on p-type CoOOH at potentials where H2O2 is reduced at a low rate only. O-2 has the ability to introduce new charge carriers into the electrode, which means that the current is limited by charge transfer kinetics and not the electrical properties of the electrode material. H2O2 cannot produce additional charge carriers, and the electrode material limits the current.
|
|
| 49. |
- Kanso, Hussein, et al.
(author)
-
Sunlight photocurrent generation from thylakoid membranes on gold nanoparticle modified screen-printed electrodes
- 2018
-
In: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 816, s. 259-264
-
Journal article (peer-reviewed)abstract
- In this work we report on the increase in photocurrent obtained by using thylakoid membranes “wired” with an osmium redox polymer (OsRP) immobilized onto screen-printed carbon and gold electrodes (SPCEs and SPAuEs), modified with gold microparticles (AuMPs) and gold nanoparticles (AuNPs). Both AuMPs and AuNPs were electrodeposited by using the same electrodeposition method in order to study the influence of different electrode surface morphologies, namely AuMPs and AuNPs, on the photocurrent generated when illuminated ΔΔΔ with light with an intensity equivalent to that of sunlight (400 W m−2). AuMPs/SPCEs showed the highest current density (62.5 μA cm−2) upon illumination probably due to a higher capacitive current directly related to the enhanced electroactive area (AEA) and roughness factor (ρ). Finally, the so modified electrodes AuMPs/SPCE and AuNPs/SPAuE were characterized by using scanning electron microscopy (SEM) showing a different surface morphology, resulting in a higher surface roughness for AuMPs/SPCE compared to AuNPs/SPAuE therefore an intimate interaction between the large thylakoid membrane and the AuNPs. A high photocurrent density of 62.5 μA cm−2 was generated at a light intensity of 400 W m−2.
|
|
| 50. |
|
|
