| 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. |
- Castillo, John, et al.
(författare)
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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
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 588:1, s. 112-121
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
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| 4. |
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| 5. |
- Eskhult, Jonas, et al.
(författare)
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On the origin of the spontaneous potential oscillations observed during galvanostatic deposition of layers of Cu and Cu2O in alkaline citrate solutions
- 2006
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 594:1, s. 35-49
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Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Evertsson, Jonas, et al.
(författare)
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Anodization of Al(100), Al(111) and Al Alloy 6063 studied in situ with X-ray reflectivity and electrochemical impedance spectroscopy
- 2017
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 799, s. 556-562
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Tidskriftsartikel (refereegranskat)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.
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| 7. |
- Fredin, Kristofer, et al.
(författare)
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The influence of cations on charge accumulation in dye-sensitized solar cell
- 2007
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 609:2, s. 55-60
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Tidskriftsartikel (refereegranskat)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.
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| 8. |
- Gonzalez-Arribas, Elena, et al.
(författare)
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A conventional symmetric biosupercapacitor based on rusticyanin modified gold electrodes
- 2018
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657. ; 816, s. 253-258
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Tidskriftsartikel (refereegranskat)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).
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| 9. |
- Hadidi, Hooman, et al.
(författare)
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Numerical investigation of capacitive deionization (CDI) with divergent and convergent channels
- 2023
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Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 944
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Tidskriftsartikel (refereegranskat)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.
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| 10. |
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