The design and fabrication of a home-made thin-layer electrochemical flow cell are reported. The performance and electrochemical characteristics of thin-layer cells are evaluated in terms of flow ...rate and channel thickness. The adaptability of the flow cell for amperometric and electrochemiluminescence measurements is demonstrated. Also, a flow injection method comprising electrochemical generation followed by spectrophotometric detection is proposed for determination of bromide using the fabricated cell. The influence of chemical, electrochemical, and flow parameters on the absorbance and current signals are investigated, and under optimized conditions, the analytical features of the proposed method with respect to bromide detection are evaluated.
Electrochemical impedance spectroscopy (EIS) and Electrochemical noise measurements (ENM) were used to evaluate protective properties of three different organic coating systems. The coatings under ...investigation were two-component aerospace coatings, applied on aluminum substrate. They were immersed in a 0.5
mol
l
−1 sodium chloride (NaCl) solution, within a controlled flow cell and were tested for 1 year.
The impedance modulus in the low frequency domain and the noise resistance were calculated and compared. From EIS data, coating capacitances and coating resistances of coating performance were estimated. The electrochemical results are in good agreement with final visual observations. The results of this study yield a performance ranking of the three different coatings.
A method has been developed for photometric detection of cyclodextrins (CD) in liquid chromatography using iodine (I₂) generated electrochemically in-situ. Iodide ion in the mobile phase was ...electrochemically oxidized to I₂ which was subsequently reacted with I⁻, in an electrochemical flow cell, forming I₃ ⁻. The absorbance of I₃ ⁻ was found to be greatly enhanced when CD were present in the mobile phase. The absorbance enhancement was caused by the change in the mole fraction of I₃ ⁻, because of the inclusion reaction of I₃ ⁻ with CD. On the basis of this phenomenon, CD were detected by means of a photodiode-array UV–visible detector positioned downstream of the electrochemical flow cell. The signals were found to be linearly dependent on CD concentration. Because the formation constants of I₃ ⁻ with CD decrease in the order α-CD>β-CD>γ-CD, α-CD was most detectable by the method. Detection limits were 1.0 μmol L⁻¹ for α-CD, 65 μmol L⁻¹ for monoG1-β-CD, 100 μmol L⁻¹ for β-CD, and 200 μmol L⁻¹ for γ-CD.
Mass-transfer measurements were made in a parallel plate cell equipped with baffles which produced a three-channel serpentine flow pattern and three-dimensional mass-transfer distribution effects. ...The entry and exit configurations were in the form of slots of rectangular cross-section. Local mass-transfer coefficient values obtained in the different channels, using surface-flush microelectrodes, reflected the complex hydrodynamics associated with phenomena such as the cell inlet and exit effects, the flow reversal effects at the baffles and preferential flow phenomena in the channels. Mass-transfer measurements obtained by averaging point measurements over various zones of the cell compared favourably with those of other workers. A hydrodynamic model of flow in the cell corresponded well to the measured mass-transfer distribution.
Ce travail porte sur la destruction quantitative et d'une manière respectueuse pour l'environnement de solutions concentrées en nitrates par deux procédés différents. Dans les deux cas, la solution ...de nitrates est d'abord réduite électrochimiquement en ammoniums sur électrode de cuivre avec une sélectivité élevée, ceci quel que soit le pH de la solution d'électrolyse. Dans le premier procédé, l'ammonium est ensuite oxydé en azote à l'aide d'ions hypochlorites générés électrochimiquement. Une excellente sélectivité réactionnelle en azote de 91,5% est obtenue avec des rendements chimiques et faradiques élevés pour la réaction de réduction des nitrates en azote, accompagnée d'une consommation énergétique basse. Le deuxième procédé est un couplage électrochimique / biologique où les solutions d'ammonium seront utilisées comme substrat azoté pour produire du biohydrogène via des boues traitées thermiquement. Une consommation complète de la solution d'ammonium provenant de la réduction des nitrates est obtenue. Un rendement maximal de 0,35 mole H2/mole de glucose est atteint en utilisant des boues activées collectées d'un bassin d'aération contre 1,1 mole H2/mole de glucose produit dans le cas des boues prélevées d'un digesteur anaérobie.
This work deals with the quantitative and environmentally friendly destruction of concentrated nitrates solutions using two different processes. In both cases, the nitrates solution was firstly reduced electrochemically into ammonium on a porous copper electrode. Whatever the initial pH of the electrolytic solution, a high ammonium selectivity was obtained. In the first process, the ammonium was subsequently oxidized to nitrogen gas by hypochlorite ions generated electrochemically. An excellent selectivity of 91.5% with high current efficiency and high chemical yield toward the nitrogen formation was recorded, with a low power consumption. The second method is an electrochemical / biological coupling process where the obtained ammonium solution will be used as a nitrogen source to produce biohydrogen (H2) via heat-treated sludge cultures. A complete assimilation of the ammonium solution resulting from the electroreduction of nitrate was obtained. A maximum hydrogen yield of 0.35 mol H2/mole glucose was achieved using activated sludge collected from an aeration tank versus 1.1 mole H2/mole glucose produced in the case of sludge taken from an anaerobic digester.
A flow-through electrochemical cell has been used for the production of conducting polymer colloids. The polypyrrole/nitrate system was selected to investigate the effect of electrochemical and ...hydrodynamic conditions on the amount and quality of the colloids produced. The colloids produced are stable and exhibit small and relatively uniform particles.
This paper demonstrates the effects on local mass transfer of placing a variety of partial obstructions in the form of fences or steps (arranged in single or multiple configurations) on the walls of ...a parallel plate electrochemical flow cell. For the wall on which the fence is placed, a plot of the position of mass transfer relative to an obstruction against the Reynolds number for different fence heights shows that, for each fence, the distance to peak position initially increases with the Reynolds number, but tends to decrease at higher Reynolds numbers. For the wall opposite to the fence, a pronounced peak immediately opposite the obstruction, corresponding to a position of maximum velocity, and a second downstream peak, corresponding to a recirculation/reattachment zone, were identified. A correlation of the peak Sherwood number as a function of the Peclet number for all fence heights and also for a backward-facing step was compared with data of other workers. The numerical prediction of flow reattachment to the walls produced excellent agreement with the positions of peak mass transfer for both the fences and the step, but agreed less well in terms of magnitude.
Summary Ashton, Sean James
Design, Construction and Research Application of a Differential Electrochemical Mass Spectrometer (DEMS),
07/2012
Book Chapter
The aim of this thesis was to design, construct and demonstrate the research application(s) of a DEMS instrument. The approach to this problem began with the analysis of previous DEMS design ...solutions before embarking on the design and construction of the DEMS instrument created in this thesis. In doing so, the intended research application of the DEMS instrument was always kept in mind: that is, to perform fundamental research studies that approach problems which are relevant to the immediate development concerns of PEMFCs.
We present a new coupled discretization approach for species transport in an incompressible fluid. The Navier-Stokes equations for the flow are discretized by the divergence-free Scott-Vogelius ...element on barycentrically refined meshes guaranteeing LBB stability. The convection-diffusion equation for species transport is discretized by the Voronoi finite volume method. In accordance to the continuous setting, due to the exact integration of the normal component of the flow through the Voronoi surfaces, the species concentration fulfills discrete global and local maximum principles. Besides of the the numerical scheme itself, we present important aspects of its implementation. Further, for the case of homogeneous Dirichlet boundary conditions, we give a convergence proof for the coupled scheme. We report results of the application of the scheme to the interpretation of limiting current measurements in an electrochemical flow cell with cylindrical shape.
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•Ti/Pt, Ti/Pt-SnSb and Nb/BDD anodes applied to a flow cells arrangement in series.•Nature of the anode material and current density affected the efficiency of individual flow ...cells.•Efficiency of flow cells system in series affected by anodes position and current density.•Colour and COD removal enhanced with energy consumption reduced.•System of two flow cells in series is an interesting alternative to treat dye effluents.
Electrochemical measurements and bulk electrolysis using individual or an assembling of flow cells in series were performed to study the anodic oxidation of amaranth dye solutions with Ti/Pt and Ti/Pt-SnSb anodes. Polarisation curves demonstrated that Ti/Pt-SnSb has high electroactivity to eliminate the pollutant. Bulk electrolysis with this material, at 30mAcm−2, removed 97.5% and 70.3% of colour and COD. Two cell configurations led to higher removal rates depending on the cell-electrode position. Additionally, experiments combining Ti/Pt-SnSb and Nb/BDD materials were performed to clarify the effect of non-active anodes in the system. Assembling cells revealed to be an interesting pre-treatment to degrade organic compounds. The suitable system choice will be dependent on the final target COD value, the reaction time and the energy consumption.
