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1.
  • Alexiadis, Alessio, et al. (författare)
  • Comparison between CFD calculations of the flow in a rotating disk cell and the Cochran/Levich equations
  • 2012
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 669, s. 55-66
  • 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)
  • 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
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 588:1, s. 112-121
  • 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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5.
  • Eskhult, Jonas, et al. (författare)
  • On the origin of the spontaneous potential oscillations observed during galvanostatic deposition of layers of Cu and Cu2O in alkaline citrate solutions
  • 2006
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 594:1, s. 35-49
  • 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)
  • Anodization of Al(100), Al(111) and Al Alloy 6063 studied in situ with X-ray reflectivity and electrochemical impedance spectroscopy
  • 2017
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 799, s. 556-562
  • 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)
  • The influence of cations on charge accumulation in dye-sensitized solar cell
  • 2007
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 609:2, s. 55-60
  • 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)
  • A conventional symmetric biosupercapacitor based on rusticyanin modified gold electrodes
  • 2018
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657. ; 816, s. 253-258
  • 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)
  • Numerical investigation of capacitive deionization (CDI) with divergent and convergent channels
  • 2023
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 944
  • 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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12.
  • Hussain, Mushtaque, et al. (författare)
  • Effect of anions on the morphology of Co3O4 nanostructures grown by hydrothermal method and their pH sensing application
  • 2014
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 717-718, s. 78-82
  • 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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13.
  • Jarolimova, Zdenka, et al. (författare)
  • All solid state chronopotentiometric ion-selective electrodes based on ferrocene functionalized PVC
  • 2013
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 709, s. 118-125
  • 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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14.
  • Johnsson Wass, J R Tobias, et al. (författare)
  • Quantum chemical modelling of oxygen reduction on cobalt hydroxide and oxyhydroxide
  • 2007
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 599:2, s. 295-312
  • Tidskriftsartikel (refereegranskat)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.
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15.
  • Kanso, Hussein, et al. (författare)
  • Sunlight photocurrent generation from thylakoid membranes on gold nanoparticle modified screen-printed electrodes
  • 2018
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 816, s. 259-264
  • Tidskriftsartikel (refereegranskat)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.
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16.
  • Karlsson, Christoffer, 1986-, et al. (författare)
  • Quinone Pendant Group Kinetics in Poly(pyrrol-3-ylhydroquinone)
  • 2014
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 735, s. 95-98
  • 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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17.
  • Larses, Patrik, et al. (författare)
  • Hydrogen evolution at mixed α-Fe1 − xCrxOOH
  • 2018
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728. ; 819, s. 114-122
  • Tidskriftsartikel (refereegranskat)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.
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18.
  • Larsson, Henrik, et al. (författare)
  • 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
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 336:1-2, s. 263-279
  • Tidskriftsartikel (refereegranskat)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.
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19.
  • Larsson, Henrik (författare)
  • 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
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 365:1-2, s. 229-237
  • Tidskriftsartikel (refereegranskat)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.
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20.
  • Li, Xianchan, 1982, et al. (författare)
  • Single cell amperometry reveals curcuminoids modulate the release of neurotransmitters during exocytosis from PC12 cells
  • 2016
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 781, s. 30-35
  • Tidskriftsartikel (refereegranskat)abstract
    • We used single cell amperometry to examine whether curcumin and bisdemethoxycurcumin (BDMC), substances that are suggested to affect learning and memory, can modulate monoamine release from PC12 cells. Our results indicate both curcumin and BDMC need long-term treatment (72 h in this study) to influence exocytosis effectively. By analyzing the parameters calculated from single exocytosis events, it can be concluded that curcumin and BDMC affect exocytosis through different mechanisms. Curcumin accelerates the event dynamics with no significant change of the monoamine amount released from single exocytotic events, whereas BDMC attenuates the amount from single exocytotic event with no significant change of the event dynamics. This comparison of the effect of curcumin and BDMC on exocytosis at the single cell level brings insight into their different mechanisms, which might lead to different biological actions. The effect of curcumin and BDMC on the opening and closing of the exocytotic fusion pore were also investigated. These results might be helpful for understanding the improvement of learning and memory and the anti-depression properties of curcuminoids.
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21.
  • Lindberg, Jonas, et al. (författare)
  • The effect of O2 concentration on the reaction mechanism in Li-O2 batteries
  • 2017
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728 .- 1873-2569. ; 797, s. 1-7
  • Tidskriftsartikel (refereegranskat)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.
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22.
  • Loupe, Neili, et al. (författare)
  • DFT - experimental IR spectroscopy of lithiated single ion conducting perfluorinated sulfonated ionomers: Ion induced polarization band broadening
  • 2017
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 800, s. 176-183
  • Tidskriftsartikel (refereegranskat)abstract
    • The impact of state of hydration and ion exchange on the exchange site local symmetry of Aquivion and Nafion perfluorinated sulfonated ionomers (PFSI) are probed by transmission IR spectroscopy.Hydrated PFSI-H membranes exhibit a pair of bands corresponding to a dissociated sulfonate exchange site with a local 3-fold axis of symmetry (C3V). C3V bands are supplanted by C1 bands (no local symmetry) corresponding to the sulfonic acid form of the exchange site. At intermediate states of hydration C3V and C1 bands co-exist. Hydrated PFSI-Li exhibits C3V bands. In contrast to PFSI-H, the PFSI-Li C3V bands persist throughout dehydration, with a final aggregate structure where each Li+ provides 1/3 of a charge per sulfonate oxygen with an overall C3V motif. The C3V band FWHM values progressively increase (hydrated PFSI-H
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23.
  • Molina Osorio, Andres, et al. (författare)
  • Modelling electrochemical modulation of ion release in thin-layer samples
  • 2021
  • Ingår i: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - : Elsevier BV. - 1572-6657. ; 903, s. 115851-
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we present a model based on the finite element approach to describe the electrochemically controlled release of ions from a redox-active film into a sample confined to a thin-layer spatial domain. The model includes the effect of interfacial charge transfer kinetics and 1D-diffusion treatment for an electron transfer-ion transfer (ET-IT) coupled reaction. More in detail, the oxidation of the redox-active film (ET) involves an ion release to an aqueous phase (IT). The dynamic concentration of the released ion is calculated when the ET-IT reaction proceeds under potentiostatic control, and the effect of the thickness of each phase (i.e., film or aqueous) on the diffusion profile is analyzed. The model is experimentally validated for the particular case in which oxidation of a thin film of polyaniline (PANI, 10 mu m in thickness) is linked to the release of protons from the film into an electrolyte solution. The proton release produces certain pH changes in the electrolyte that are monitored by a pH sensor located at 330 mu m from the PANI film. The charge associated with the proton release is related to the dynamic concentration of protons in the electrolyte through pH-coulograms that agree with the theoretical predictions. Overall, the model can reproduce the general behavior of the experimental proton pump and provides key insights into the functioning mechanism of electrochemical systems where redox and ion transfer reactions are coupled.
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24.
  • Momodu, Damilola, et al. (författare)
  • Stable ionic-liquid-based symmetric supercapacitors from Capsicum seed-porous carbons
  • 2019
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 838, s. 119-128
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, a symmetric ionic-liquid based supercapacitor was assembled with porous carbon derived from Capsicum (bell pepper) seeds. The “peppered”-activated carbon (ppAC) was synthesized using varying amounts of KHCO 3 activating agent (AA) at 850 °C carbonization temperature. The best device performance reported was recorded with optimum amounts of AA to raw material. The need for less amount of AA is crucial if the entire activation/carbonization process is to be scaled-up with the cost and final product yield also being important for a viable synthesis. A mechanism of saturation of pores with unreacted AA which leads to lower porosity metrics in the samples with increasing the amount of AA during carbonization/activation was also proposed. Using an ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bistrifluorosulfonylimide (EMIM-TFSI), the ppAC-based supercapacitor operated up to a maximum cell voltage of 3.20 V. A specific energy of 37 Wh kg −1 was obtainable with a corresponding practical power density of 0.6 kW kg −1 at 0.5 A g −1 . A specific energy of ∼26 Wh kg −1 was still achievable when the applied current was doubled to 1.0 A g −1 and a high cyclic stability (approx. 99% coulombic efficiency) was proven over 25,000 cycles. Further ageing test performed on the device revealed a remarkable improvement in the electrochemical performance after a 180 h (ca. 1 week) floating time. The obtained results also confirmed a uniquely distributed porous carbon in which the complete utilization of the entire less-corrosive KHCO 3 AA for optimal pore activation at elevated carbonization temperatures. Thus, the efficient design combinations for stable, high-energy and power ionic liquid-based supercapacitors with cheaper biomass-based materials are demonstrated.
  •  
25.
  • Munktell, Sara, et al. (författare)
  • Towards high throughput corrosion screening using arrays of bipolar electrodes
  • 2015
  • Ingår i: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - : Elsevier BV. - 1572-6657. ; 747, s. 77-82
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work we demonstrate the possibility of combining bipolar electrochemistry with arrays of samples as a fast and versatile method for comparing their corrosion resistances at a wide range of potentials. Several steel samples of different grades were arranged in a bipolar electrochemical cell and exposed to an electric field by applying a constant current. The gradient in electrochemical potential difference across each sample resulted in a pitting corrosion gradient on the anodic parts which was used as a simple, straightforward and qualitative method of screening the corrosion properties of several samples in one single experiment. In the cell, all samples acted as individual bipolar electrodes but interestingly, the current density for each sample was also found to be influenced by the corrosion resistances of its neighbours. Results from the bipolar array were also compared with standard polarisation curves and the pitting resistance equivalent number (PREN) for each steel type.
  •  
26.
  • Munteanu, Florentina, et al. (författare)
  • NADH electrooxidation using carbon paste electrodes modified with nitro-fluorenone derivatives immobilized on zirconium phosphate
  • 2004
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 564, s. 167-178
  • Tidskriftsartikel (refereegranskat)abstract
    • The basic electrochemistry of carbon paste electrodes modified with two new redox mediators, nitro-fluorenone derivatives, one neutral and one negatively charged, adsorbed on zirconium phosphate has been studied as well as their ability to oxidize NADH electrocatalytically. Cyclic voltammetry of these chemically modified electrodes performed in different aqueous buffer solutions at different pHs revealed that the immobilized redox species present very stable redox properties and the formal potential is virtually independent of the pH and/or the constituents of the contacting solution. The second order rate constants for the electrocatalytic oxidation of NADH were evaluated from rotating disk electrode experiments, and found to be of the order of between 106 and 107 M−1 s−1, among the highest reported so far compared with literature values. The catalytic efficiency can be enhanced by addition of Ca2+ ions to the electrolyte solution and it is shown that Ca2+ affects both the neutral and negatively charged mediator.
  •  
27.
  • Mwanza, Daniel, et al. (författare)
  • Capacitive label-free ultrasensitive detection of PSA on a covalently attached monoclonal anti-PSA antibody gold surface
  • 2022
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657. ; 927
  • Tidskriftsartikel (refereegranskat)abstract
    • A rapid, low-cost, and accurate point-of-care analytical device for the determination of prostate-specific antigen (PSA) is required for the early diagnosis and prognosis of prostate cancer (PCa). In this work, an electrochemical capacitive immunosensor was developed for the label-free detection of PSA. The immunosensor was based on the covalent immobilization of monoclonal anti-PSA antibody via carbodiimide chemistry onto gold electrode (AuE) pre-modified with a thin monolayer film of isophthalic acid (IPA). A methodology based on the steric hindrance of 1,3-substituted aryldiazonium salt was adopted to control the growth of the IPA thin film on the gold electrode. The non-specific binding sites were blocked with bovine serum albumin (BSA) to afford an AuE-IPA-anti-PSA-mAb|BSA immunosensor. The immunosensor was characterized by X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The analytical performance of the developed sensor was evaluated using the capacitance Nyquist plots generated from the complex impedance data. In addition, complex capacitance was also calculated from the imaginary part of the impedance and plotted against the log of frequency. The double layer capacitance from the circuit fitting (RSC) was also used and compared the sensitive capacitance signals to the changes in PSA concentrations. The LOD values were in fg.mL−1 and distinguishable from the blank (PBS) for the Nyquist plots of capacitance, complex capacitance, and double layer capacitance signals. The developed immunosensor exhibited good stability, selectivity, low detection limits, and a wide linear range which was suitable for screening of prostate cancer using prostate-specific antigen.
  •  
28.
  • Nasef, Hany, et al. (författare)
  • Electrochemical molecular beacon DNA biosensor for the detection and discrimination of the DF508 cystic fibrosis mutation
  • 2011
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 662:2, s. 322-327
  • 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.
  •  
29.
  • Nazarov, Andrej P., et al. (författare)
  • Electrochemical and corrosion properties of ZnO/Zn electrode in atmospheric environments
  • 2015
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier B.V.. - 1572-6657. ; 737, s. 129-140
  • Tidskriftsartikel (refereegranskat)abstract
    • ZnO films of different thicknesses were prepared by thermal oxidation of zinc. The oxide covered surfaces were characterized by Scanning Kelvin Probe (SKP) and Scanning Kelvin Probe-Surface Photovoltage (SKP-SPV) techniques, Infrared Reflection Absorption Spectroscopy (IRRAS), contact angle measurements, and dc voltammetry. The influence of the thickness of ZnO on the absorption of the light, water and oxygen was evaluated. SKP and dc electrochemistry were used to estimate the mechanism of electron exchange between the zinc surface and an aqueous solution containing a red-ox system [Fe(CN)6]2-/[Fe(CN)6]3-. It was shown that ZnO/Zn electrodes with a thick ZnO film nobled the Volta potential that enhanced the electron transfer from the bulk zinc to the molecule of the oxidizer- [Fe(CN)6]3-. Atmospheric corrosion of oxidized zinc surface was investigated after deposition of a single droplet of NaCl aqueous electrolyte. Thicker ZnO films promote the oxygen reduction and the spreading area of the cathodic reaction from the local NaCl contamination. It enlarged the area of metal surface participating in the cathodic reaction and consequently accelerated the atmospheric corrosion. The ability to enhance the oxygen reduction was discussed from the point of view of the band structure and the semiconducting properties of the ZnO layer.
  •  
30.
  • Nissfolk, Jarl, et al. (författare)
  • Interpretation of small-modulation photocurrent transients in dye-sensitized solar cells : A film thickness study
  • 2010
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 646:1-2, s. 91-99
  • 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.
  •  
31.
  • Papaderakis, Athanasios, et al. (författare)
  • Ternary IrO2-Pt-Ni deposits prepared by galvanic replacement as bifunctional oxygen catalysts
  • 2020
  • Ingår i: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - : ELSEVIER SCIENCE SA. - 1572-6657. ; 877
  • Tidskriftsartikel (refereegranskat)abstract
    • Bifunctional oxygen catalysts with IrO2 and Pt active components have been prepared by means of galvanic partial replacement of Ni layers electrodeposited on glassy carbon substrates (Ni/GC). The resulting IrO2Pt(Ni)/GC electrodes have a homogeneous and compact morphology (SEM), while surface electrochemistry and spectroscopic measurements (EDS, XPS) confirm the ternary bulk structure (EDS: 56.39% Ir- 7.60% Pt - 36.01% Ni atomic ratio) and the existence of a IrO2-Pt thin skin on the outermost layers of the deposits (XPS: Ir+ Pt atomic ratio of 21.7). IrO2Pt (Ni)/GC electrodes were evaluated as bifunctional electrocatalysts for oxygen evolution (OER) and oxygen reduction (ORR) reactions in acid, by means of steady-state current-potential measurements and linear sweep voltanunetry at a Rotating Disc Electrode (RDE) respectively. The OER overpotential required for a current density (per substrate geometric area) of 1 (eta(1)) and 10 mA cm(-2) (eta(10)) on the prepared electrodes was 235 and 302 my respectively, which is in the range of some typical thermally produced IrO2-based DSAs. Their intrinsic OER catalytic activity (as estimated by normalization of the recorded currents at an overpotential of 260 mV by the oxides charge) was found to be 0.29 mA mC(-1) comparable or better to other thermally produced IrO2 and Pt-IrO2 systems. Koutecky-Levich analysis shows that ORR proceeds on the ternary catalysts via the four electrons pathway. The overall ORR catalytic activity (0.4 mA cm(-2) at +0.8 V vs. SIIE) is found to be in the range of that recorded on nanoparticle catalysts, while a suppression of the intrinsic activity compared to bulk Pt is observed most probably due to the presence of IrO2, the latter being in line with similar non-alloyed Pt-IrO2 systems reported in the literature.
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32.
  • Paulsson, Heléne, et al. (författare)
  • Electron transport and recombination in dye-sensitized solar cells with ionic liquid electrolytes
  • 2006
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 586:1, s. 56-61
  • Tidskriftsartikel (refereegranskat)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.
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33.
  • Phal, Sereilakhena, et al. (författare)
  • Covalently electrografted carboxyphenyl layers onto gold surface serving as a platform for the construction of an immunosensor for detection of methotrexate
  • 2018
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657 .- 1873-2569. ; 812, s. 235-243
  • Tidskriftsartikel (refereegranskat)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.
  •  
34.
  • Quentel, Francois, et al. (författare)
  • Studying ion transfers across a room temperature ionic liquid vertical bar aqueous electrolyte interface driven by redox reactions of lutetium bis(tetra-tert-butylphthalocyaninato)
  • 2007
  • Ingår i: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - 1572-6657. ; 611, s. 192-200
  • Tidskriftsartikel (refereegranskat)abstract
    • Ion transfer reactions across the interface between an aqueous electrolyte solution and the room temperature ionic liquid (RTIL) 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([hmim][fap]) were studied with the help of three-phase electrodes. The electrode assembly comprised an edge plane pyrolytic graphite electrode modified with a thin layer of [hmim][fap] containing lutetium bis(tetra-tert-butylphthalocyaninato) (Lu[tBu(4)Pc](2)) as redox probe. Lu[tBu(4)Pc]2 can be oxidized and reduced to a stable hydrophobic monovalent cation and anion, respectively, hence allowing investigation of the transfer of cations and anions in one and the same voltammetric experiment. In spite of the strong hydrophobicity of the salt [hmim][fap], the electrode reactions of he redox probe studied in contact with various inorganic aqueous electrolytes, were frequently accompanied by expulsion of ions constituting the RTIL into the aqueous phase. Using ion chromatography it was found that the distribution of ions in the aqueous electrolyte/RTIL biphasic system is strongly determined by ion exchange reactions. The affinity of the ions of the RTIL for the aqueous phase was assessed using the water-nitrobenzene (W-NB) system, and the following Gibbs energies of ion transfer were found: Delta(W–>NB) G([hmim]+)(circle minus) = -16.6 +/- 0.9 kJ mol(-1) and Delta(W-NB) G([fap]-)(circle minus) 22.4 +/- 0.3 kJ mol(-1). (C) 2007 Elsevier B.V. All rights reserved.
  •  
35.
  • Rajendra Babu Kalai Arasi, Azega, 1995, et al. (författare)
  • Effect of plasma treatment on electrochemical performance of lignin-based carbon fibers
  • 2023
  • Ingår i: Journal of Electroanalytical Chemistry. - 1572-6657. ; 946
  • Tidskriftsartikel (refereegranskat)abstract
    • The abundant and renewable nature of lignin obtained from wood renders it as a sustainable carbon resource for energy storage applications. However, their environmentally unfavorable processing conditions and limited energy storage performance prohibit the use of lignin-based carbon materials' use as supercapacitor electrodes. The material's properties require advancement to overcome the limitation of low specific capacitances. In this study, we report on the impact on the electrochemical performance of inherently hydrophobic lignin-based carbon fibers (LCF) by subjecting them to a mild plasma treatment. The electrode’s capacitance was thus increased by 20%, with better rate capability and energy-power performance (11 Wh/kg and 0.8 kW/kg) in the KOH electrolyte. The quantified improvements were attributed to the capacitive functional groups, and enhanced surface wettability, which increased ion accessibility to active surface area improving charge-transfer ability to the surface with more additional functional groups. Remarkably, the selected plasma conditions introduced mostly desirable functional groups that limited any parasitic faradaic reactions prone to affect the device's long-term cycling stability and self-discharge characteristics. Furthermore, the impact of different inherent and introduced oxygen surface functional groups, including COO−, COH, CO, and CO, on the capacitive performance of these fibers at different device conditions (such as cycling and electrochemical activation) was investigated in different aqueous electrolytes. To ensure environmental favorability, the electrospinning of lignin fibers was conducted using a high molecular fraction of lignin without the inclusion of any fossil-based co-spinning polymers.
  •  
36.
  • Ruiz, Vanesa, et al. (författare)
  • A study of Faradaic phenomena in activated carbon by means of macroelectrodes and single particle electrodes
  • 2008
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 618:1-2, s. 33-38
  • Tidskriftsartikel (refereegranskat)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.
  •  
37.
  •  
38.
  • Shao, Cairu, et al. (författare)
  • Influence of Cr doping on the oxygen evolution potential of SnO2/Ti and Sb-SnO2/Ti electrodes
  • 2019
  • Ingår i: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - : ELSEVIER SCIENCE SA. - 1572-6657. ; 832, s. 436-443
  • Tidskriftsartikel (refereegranskat)abstract
    • Oxygen evolution potential is the determining factor affecting the anode efficiency of the wastewater treatment process. In this study, we focus on increasing oxygen evolution potential of Cr-SnO2/Ti and Cr-Sb-SnO2/Ti electrodes with the pyrolytic method. XRD, SEM and XPS techniques had been applied to characterize the microstructures and chemical compositions of the samples. Electrochemical measurements had been performed to evaluate the oxygen evolution potential as a criterion of the wastewater treatment efficiency. The results show that co-doping of Sb and Cr improved the crystallinity and grain size of SnO2 coating, and Cr existed in the form of Cr(III) valence states. The Cr doping treatment improved the electronic conductivity and the electrocatalytic activity of the electrodes. DFT calculation of the band-structure indicates Cr doped SnO2 had a superior electrical conductivity, where Cr atom acts as an acceptor providing vacancies for electron transportation. The DOS diagrams reveal the Cr doped SnO2 showing a p-type conductivity which would subsequently influence the built-in potential on metal-semiconductor interface. We proposed the mechanism of the increase of oxygen evolution potential is the doping of Cr expands the built-in potential.
  •  
39.
  • Sjödin, Martin, 1974-, et al. (författare)
  • Proton-coupled electron transfer from an interfacial phenol monolayer
  • 2020
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 859
  • Tidskriftsartikel (refereegranskat)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.
  •  
40.
  • Sjödin, Martin, 1974-, et al. (författare)
  • Reprint of "Proton-coupled electron transfer from an interfacial phenol monolayer"
  • 2020
  • Ingår i: Journal of Electroanalytical Chemistry. - : ELSEVIER SCIENCE SA. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 875
  • Tidskriftsartikel (refereegranskat)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.
  •  
41.
  • Steegstra, Patrick, 1978, et al. (författare)
  • In situ pH measurements with hydrous iridium oxide in a rotating ring disc configuration
  • 2012
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 685, s. 1-7
  • 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.
  •  
42.
  • Tavahodi, Mojtaba, et al. (författare)
  • Interaction of polymer-coated gold nanoparticles with cellobiose dehydrogenase : The role of surface charges
  • 2018
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 819, s. 226-233
  • Tidskriftsartikel (refereegranskat)abstract
    • Studying the interaction of functional proteins such as enzymes and nanoparticles (NPs) includes the important topic of investigating any possible changes in stability and function of enzymes in nanostructured environments. The effects of NPs on the enzyme activity and stability are governed by their physical and chemical properties such as structure, shape, size, surface chemistry and their surface charges. In this study, the influence of negatively and positively charged AuNPs are investigated on the activity of immobilized Myriococcum thermophilum cellobiose dehydrogenase (MtCDH) and its electron transfer rate with graphite electrodes modified with positively and negatively AuNPs. The MtCDH modified graphite electrode premodified with positively charged AuNPs showed an alkaline shift in the pH of maximum activity from pH5.5 to 8. No change in the pH of maximum activity was observed when MtCDH graphite electrodes were premodified with negatively charged AuNPs. The results clearly demonstrated the effect of surface charge of AuNPs on the activity of the enzyme. The catalytic current density and the KM app value for MtCDH graphite electrode premodified with positively charged AuNPs were enhanced with up to 66 and 8 times, respectively. Two spectroscopic assays were also performed in solution to investigate the influence of the presence of positively or negatively charged AuNPs on the activity of MtCDH in homogeneous solution. The results clearly demonstrated that not only the rate of the heterogeneous electron transfer between the immobilized MtCDH and the electrode but also the rate of the homogeneous electron transfer between soluble MtCDH and the acceptor was highly dependent on the type of surface charge of the AuNPs.
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43.
  • Tripachev, Oleg, et al. (författare)
  • Gold autodeactivation during oxygen electroreduction studied by electrochemical impedance spectroscopy
  • 2012
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 683, s. 21-24
  • 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.
  •  
44.
  • Waita, Sebastian M., et al. (författare)
  • Electrochemical Characterization of TiO2 Blocking Layers Prepared by Reactive DC Magnetron Sputtering
  • 2009
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 0022-0728 .- 1873-2569 .- 1572-6657. ; 637:1-2, s. 79-83
  • Tidskriftsartikel (refereegranskat)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.
  •  
45.
  • Waita, Sebastian M., et al. (författare)
  • Electron transport and recombination in dye sensitized solar cells fabricated from obliquely sputter deposited and thermally annealed TiO2 films
  • 2007
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657 .- 0022-0728 .- 1873-2569. ; 605:2, s. 151-156
  • Tidskriftsartikel (refereegranskat)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.
  •  
46.
  • Wiberg, Cedrik, 1989, et al. (författare)
  • Naphthalene diimides (NDI) in highly stable pH-neutral aqueous organic redox flow batteries
  • 2021
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 896
  • Tidskriftsartikel (refereegranskat)abstract
    • In the pursuit of environmentally friendly energy storage, aqueous organic redox flow batteries (AORFBs) that use naphthalene diimide hold promise for successful application. In the present article, two different naphthalene diimides (NDI) are studied as negative electrolyte materials for pH-neutral aqueous organic/ organometallic redox flow batteries. The two molecules, one core-unsubstituted NDI (2H-NDI) and one coredimethylamino substituted NDI (2DMA-NDI) are coupled with a solubilized ferrocene (BTMAP-Fc) at a concentration of 50 mM in phosphate buffered potassium chloride. High energy efficiencies and coulombic efficiencies were obtained for both batteries, but a gradual capacity fade was observed while cycling. However, when changing the cation of the supporting electrolyte from potassium to ammonium, similar energy and coulombic efficiencies were obtained, but with undetectable capacity losses over 320 cycles. Finally, 2H-NDI and BTMAPFc at 500 mM were tested in the ammonium-based electrolyte, and while obtaining high coulombic efficiency, the energy efficiency and cycling stability decreased compared to the same system at lower concentration. It is concluded that loss of activity is mainly due to formation of electrochemically inactive compounds and that the electrolyte cation is of great importance for the outcome. Important design strategies for AORFB molecules include using supporting salts that prevent self-association and introducing sterically hindering substituents to the structures.
  •  
47.
  • Wreland Lindström, Rakel, et al. (författare)
  • Electrocatalysis and transport effects on nanostructured Pt/GC electrodes
  • 2010
  • Ingår i: J ELECTROANAL CHEM. - : Elsevier BV. - 1572-6657 .- 0022-0728. ; 644:2, s. 90-102
  • Tidskriftsartikel (refereegranskat)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.
  •  
48.
  • Ye, Chen-Qing, et al. (författare)
  • EIS analysis on chloride-induced corrosion behavior of reinforcement steel in simulated carbonated concrete pore solutions
  • 2013
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier BV. - 1572-6657. ; 688, s. 275-281
  • Tidskriftsartikel (refereegranskat)abstract
    • The corrosion behavior of reinforcement steel in simulated carbonated concrete pore (SCCP) solution containing different concentrations of chloride was studied by electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) measurements simultaneously, and the topographies of the steel specimens and the elemental distribution at corrosion area were examined by scanning electron microscope (SEM)/electron microprobe analysis (EMPA). The results showed the capacitive loop and polarization resistance decreased with chloride increasing. Furthermore, when the chloride concentration reached a critical value, the Bode plots obviously exhibited two phase angle peaks indicating two time constants. However, when the chloride content exceeded a critical value, the phase angle peaks decreased to one phenomenal peak. An equivalent circuit with two RC loops was used to characterize the corrosion behavior of reinforcement steel in SCCP solution according to the measurements of EIS. Based on the dependence of the equivalent circuit elements on chloride content and immersion time, the formation, growth and breakdown of passive film of the steel were discussed. It was found that the EIS evaluation of corrosion behavior for reinforcement steel in SCCP solution was good agreement with the LPR and SEM measurements. The EMPA mapping revealed MnS inclusions at steel surface play a leading role in the initiation of pitting corrosion.
  •  
49.
  • Žalnėravičius, Rokas, et al. (författare)
  • Nanoplatelet MoS2 arrays decorated with Pt nanoparticles for non-enzymatic detection of hydrogen peroxide
  • 2019
  • Ingår i: Journal of Electroanalytical Chemistry. - : Elsevier. - 1572-6657. ; 839, s. 274-282
  • Tidskriftsartikel (refereegranskat)abstract
    • An electrochemical detection platform for monitoring of hydrogen peroxide was designed based on molybdenum disulphide nanocomposites. Bulk MoS2 as well as flower-like MoS2 sheets on Ti substrate were synthesized via a hydrothermal approach. Monodispersed MoS2 nanoparticles with average size less than 2 nm were fabricated by simple and low-cost ultrasonication and gradient centrifugation method. The MoS2/Ti structures were further assessed for amperometric H2O2 detection. The nanoflower MoS2/Ti electrode were electrochemically designed with highly dense Pt nanoparticles. The structure and surface morphology were subsequently characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The electrochemical behaviours and sensing performances of the MoS2/GC, MoS2/Ti and Pt/MoS2/Ti electrodes were studied by cyclic voltammetry (CV) and chronoamperometry. The MoS2 nanoparticle modified GC electrode displayed excellent sensitivity towards H2O2 at applied voltage of -0.6 V and the best sensitivity of 1.93 mu A mu M-1 cm(-2) was reached with Pt/MoS2/Ti electrodes. The electrodes prepared by using novel hybrid MoS2 nanomaterials showed high sensitivity, selectivity and long-term stability (at least 10 days) for monitoring of H2O2 and, thus, deserve further studies of their application in development of sensors and biosensors.
  •  
50.
  • Zaman, Siama, et al. (författare)
  • CuO nanoflowers as an electrochemical pH sensor and the effect of pH on the growth
  • 2011
  • Ingår i: JOURNAL OF ELECTROANALYTICAL CHEMISTRY. - : Elsevier. - 1572-6657. ; 662:2, s. 421-425
  • Tidskriftsartikel (refereegranskat)abstract
    • Well-crystallized flower-shaped cupric oxide (CuO) nanostructures composed of thin leaves have been synthesized by simple low-temperature chemical bath method and used to fabricate pH sensor. We examined the effect of the pH on the growth of the CuO nanostructures, by changing the pH of the precursor solutions different morphologies of the CuO nanostructures were obtained. CuO nanoflowers have recently become important as a material that provides an effective surface for electrochemical activities with enhanced sensing characteristics. The proposed sensor exhibited a linear electrochemical response within a wide pH range of (2-11). The experimental results (time response, electrochemical activity, reproducibility, absorption spectra, and XRD) indicate that the CuO nanoflowers can be used in pH sensor applications with enhanced properties.
  •  
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