Actual Electrode Research Articles

Efficient Reduction of CO[sub 2] in a Solid Oxide Electrolyzer

When the economy is based on renewable energy resources, such as wind and solar, the major source of H2 for chemical production and energy storage will be from the electrolysis of water. The ability to reduce CO2 efficiently by a similar process could also play a role in reducing greenhouse gas emissions and moving us toward a more sustainable economy. 1 CO produced in this manner could be used in chemical production or reacted with H2 to produce liquid fuels via the Fischer‐Tropsch reaction. 2 Solid oxide electrolyzers SOEs, which are essentially solid oxide fuel cells SOFCs operated in reverse, are capable of higher water electrolysis efficiencies compared to solution-based electrolysis cells because they operate at higher temperatures 925 K. The higher operating temperatures result in a lower Nernst potential, the thermodynamic potential required for water splitting, and in lower electrode overpotentials. 3 The electrode overpotential is the difference between the actual electrode potential and the Nernst potential, and is a measure of the lost efficiency in the cell. SOEs also differ from low-temperature, solution-based electrolyzers in that the electrolyte membrane conducts oxygen anions, rather than protons. The material most often used for the electrolyte is yttria-stabilized zirconia YSZ, a material that is a good oxygen-anion conductor and an electronic insulator. In an SOE, the cathode the fuel-side electrode reaction for water electrolysis is the electrochemical dissociation of steam to produce H2 and O 2 anions, Reaction 1, while recombination of the oxygen ions to O2, Reaction 2, occurs at the anode the air-side electrode H2 O+2 e  → O 2 +H 2

Modified Mathematical Models for Melting Rate in Submerged Arc Welding

Modified mathematical models for melting rate during submerged arc welding with straight and reverse polarities have been proposed. The present work is a result of a critical analysis of existing models and subsequent modification in order to improve the predictability and practicability. The proposed models bridge the gap between less scientific shop-fioor-friendly models and scientifically correct but not so shop-floor- friendly models. Instead of experimental measurement of electrode extension or making the assumption that the electrode extension is equal to contact tube to work-piece distance, the present work models the role of electrode extension during melting by considering the effect of process parameters on it. On the other hand, influence of process parameters on arc heating has also been incorporated. The developed models cover the effect of fundamental parameters like current, voltage, electrode extension and wire diameters. Simulated annealing has been used to calibrate the proposed models and subsequently the models are validated with data points different from the points used for model calibration. The modified models provide better accuracy than the models that have been constituted with the above stated assumption as well as it is more practical than those models in which actual electrode extension has been experimentally measured. The outcome of investigation has been analyzed in terms of improvement in the predictability, resemblance with physics of the process and generalization capacity of the models. The approach of the present work is applicable for future research in other welding processes.

Electrochemical Behavior of Nanocrystalline Ru0.8Me0.2O2 − x ( Me = Fe , Co , Ni ) Oxide Electrodes in Double-Layer Region

Nanocrystalline oxides with average chemical composition corresponding to were prepared by the sol-gel approach. All prepared materials were of single-phase character with rutile-type structure. The effect of nanocrystal size and nature of doping cation on electrochemical supercapacitor behavior was studied by means of cyclic voltammetry and electrochemical impedance. The specific capacitance of the Ru-based oxides increases by doping with lower-valence cation from ca. of actual electrode surface area observed for pure to in the case of Ni doped material. The improved capacitance behavior of the doped materials is ascribed to improvement of transport properties of the oxide structure enabling easier diffusion of compensating protons.

Electrochemical Behavior of Surface-Fluorinated Natural Graphite in Propylene Carbonate-Containing Solvent

Surface fluorination of natural-graphite samples with average particle sizes of 5, 10, and (abbreviated to , , and ) was performed by at 200 and for and electrochemical properties of surface-fluorinated natural-graphite samples were investigated in –ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PC) (1:1:1 in volume). Surface fluorine concentrations were in the range of 11.1–15.3 and for natural-graphite samples fluorinated at 200 and 300°C, respectively, for three natural-graphite samples. The surface areas of and were only slightly increased by fluorination, while the increase in surface area was large in the case of . However, the increase in surface disorder by fluorination was larger for and than for . Electrochemical reduction of PC on and was highly reduced by surface fluorination, which led to a large increase in first coulombic efficiencies. The increase in first coulombic efficiencies for surface-fluorinated and is attributed to the increase in their surface disorder and probably actual electrode area by fluorination.

Imaging of conductivity changes and electrode movement in EIT

Electrical impedance tomography (EIT) attempts to reconstruct the internal impedance distribution in a medium from electrical measurements at electrodes on the medium surface. One key difficulty with EIT measurements is due to the position uncertainty of the electrodes, especially for medical applications, in which the body surface moves during breathing and posture change. In this paper, we develop a new approach which directly reconstructs both electrode movements and internal conductivity changes for difference EIT. The reconstruction problem is formulated in terms of a regularized inverse, using an augmented Jacobian, sensitive to impedance change and electrode movement. A reconstruction prior term is computed to impose a smoothness constraint on both the spatial distribution of impedance change and electrode movement. A one-step regularized imaging algorithm is then implemented based on the augmented Jacobian and smoothness constraint. Images were reconstructed using the algorithm of this paper with data from simulated 2D and 3D conductivity changes and electrode movements, and from saline phantom measurements. Results showed good reconstruction of the actual electrode movements, as well as a dramatic reduction in image artefacts compared to images from the standard algorithm, which did not account for electrode movement.

Subthalamic stimulation for Parkinson disease: determination of electrode location necessary for clinical efficacy

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) performed using intraoperative microelectrode recording (MER) to adjust electrode placement has become a widely used treatment for patients with advanced Parkinson disease (PD). Few studies have been conducted to examine the location of implanted electrodes relative to the intended target, and even fewer have been undertaken to investigate the degree to which variations in the location of these electrodes impacts their clinical efficacy. This study was performed to examine these issues. The authors located 52 bilaterally implanted DBS electrode tips on postoperative magnetic resonance (MR) images obtained in 26 consecutive patients. Postoperative and preoperative planning MR images were merged to determine the DBS electrode tip coordinates relative to the midcommissural point. Surgical records listed the intended target coordinates for each DBS electrode tip. Clinical outcome assessment included the Unified PD Rating Scale (UPDRS) motor score at 1 year, standardized questionnaires, and routine follow-up visits. The mean difference between electrode tip location and intended target for all 52 electrodes was less than 2 mm in all axes. Only one electrode was farther than 3 mm from the intended target, and this was the only electrode that had to be replaced due to lack of clinical efficacy (lack of tremor suppression); its reimplantation 4 mm more medially provided excellent tremor control. High correlation coefficients indicate that the MR imaging analysis accurately determined the anatomical location of the electrode tips. Blinded videotape reviews of UPDRS motor scores comparing effects of stimulation in patients who were "on" and "off" medication identified subgroups in whom there was minimal and maximal stimulation response. Patients in these subgroups had no differences between the MR imaging-determined actual electrode tip location and its intended location. Similarly, improvements of dyskinesias and severity of symptoms encountered during the wearing-off period for the drug did not correlate with variations of electrode tip location. The findings in this study lead the authors to suggest that a DBS electrode placed anywhere within a 6-mm-diameter cylinder centered at the presumed middle of the STN (based on stereotactic atlas coordinates) provides similar clinical efficacy. Future studies may be warranted to evaluate prospectively the degree to which MER modification of the anatomically and/or image-determined target improves clinical efficacy of DBS electrodes.

Deep Brain Stimulation in Intraoperative MRI Environment - Comparison of Imaging Techniques and Electrode Fixation Methods

We performed 118 consecutive DBS cases from November 1999 to June 2002. Intraoperatively there were 10 cases studied with fluoroscopy, 73 with 0.2 Tesla (T) MRI and 35 with 1.5 T MRI. Ten electrodes were secured by Medtronic caps, 25 by methyl methacrylate with titanium miniplates, and 82 by Navigus caps. The 3-dimensional displacement between the planned target and actual electrode position (3DD) was determined by fusing the postoperative MRI with the preoperative imaging. The 3DD for using Medtronic caps, methyl methacrylate with miniplates, and Navigus caps were 4.80 +/- 3.16, 2.64 +/- 1.26 and 2.23 +/- 1.15 mm (mean +/- SD), respectively. Navigus caps had statistically significant accuracy (P = 0.03) in holding the electrode when compared with Medtronic caps, and it facilitated electrode revision. The fixation devices significantly affect the final vertical position of the electrode. The 3DD for fluoroscopy, 0.2 T and 1.5 T MRI cases were 4.80 +/- 3.16, 2.31 +/- 1.21 and 2.34 +/- 1.14 mm (mean +/- SD), respectively. No statistically significant difference (P = 0.91) in 3DD was demonstrated between 0.2 T and 1.5 T MRI cases. The presence of intraoperative 1.5 T MRI allowed near real-time electrode position confirmation and early detection of hemorrhagic complications. Satisfactory microelectrode recording was feasible in low-field 0.2 T and high-field 1.5 T MRI environments. Further studies on performing DBS in real-time intraoperative MRI are warranted.

A CFD STUDY OF FLOWS IN SLAG CLEANING FURNACES

A computational fluid dynamics (CFD) study of a three-dimensional magneto-hydrodynamic flow is conducted for an industrial scale slag cleaning furnace with three electrodes immersed into the slag by using idealized and actual electrode shapes. The trajectories of nickel droplets are calculated which demonstrates the potential areas of nickel droplet settling. Calculations are also carried out for varied boundary conditions along the free surface of the slag and the furnace wall. Some effect of the electrode shape on the slag flow and metal droplet settling is observed, but a similar flow and heat transfer behaviour is revealed using the cylindrical electrode. It is important to correctly present the boundary conditions at the free surface and the furnace wall in order to obtain reasonable predictions for the slag flow and heat transfer. Numerical predictions are validated with the experimental data measured in an operating slag cleaning furnace.On effectue une étude numérique de dynamique des fluides (CFD) de l’écoulement magnétohydrodynamique tridimensionnel d’un four à échelle industrielle de nettoyage de scorie. À cet effet, on a employé trois électrodes immergées dans la scorie en utilisant des formes idéalisées et actuelles d’électrode. On calcule les trajectoires des gouttelettes de nickel, ce qui démontre les zones potentielles de sédimentation de gouttelette de nickel. On effectue également des calculs pour des conditions limites variées le long de la surface libre de la scorie et de la paroi du four. On observe un certain effet de la forme de l’électrode sur l’écoulement de la scorie et sur la sédimentation de la gouttelette de métal, mais un comportement relativement similaire d’écoulement et de transfert de chaleur est révélé avec l’électrode cylindrique. Il est important de présenter correctement les conditions limites à la surface libre et à la paroi du four afin d’obtenir des prédictions raisonnables d’écoulement et de transfert de chaleur de la scorie. On valide les prédictions numériques avec les données expérimentales mesurées dans un four opérationnel de nettoyage de scorie.

Influence of the local variation of the polarization resistance on SOFC cathodes

According to the electrode theory widely accepted, the polarization resistance ( R p) of SOFC oxygen electrodes should be independent of the electrolyte resistivity ( ρ). This is a natural consequence from the usual theory, since it assumes that R p is only determined by the interaction between the electrode and gas phase. However, it has been recently found that R p increases with ρ. This observation suggests that the R p-determining factor should involve an electrolyte factor. This paper is an attempt to explain the R p vs. ρ relationship as being due to the locally variable polarization resistance of the electrode. Since the actual electrode makes discrete contacts with the electrolyte surface and the polarization resistance is more or less locally variable, it can be regarded as an assembly of many electrode elements having various local performances. When a load current is applied to such an electrode, an interfacial resistance ( r i) arises due to a geometrical effect of the discrete contacts. By taking the effect of r i into account, it was predicted that R p increases with increasing r i. The validity of the theory was tested by checking whether or not the r i increases with increasing ρ. The r i was measured by extrapolating the resistance of the electrolyte vs. sample length to zero length. In fact, r i increases with increasing ρ. To obtain experimental evidence for the locally variable polarization, we measured the decay curves as a function of pO 2. The slope of the decay curve increases with increasing pO 2, suggesting that there is a local difference of polarization which drives an interfacial ionic current through the short-circuit pathway. We also tested this mechanism by an artificial nonuniform electrode which had a substructure consisting of two electrode elements, Ag and Au pastes electrodes. A polarization difference between the two electrode elements was found to increase with increasing ρ of the electrolyte, as expected from the local current mechanism. This theory involves no mechanism of the local polarization resistance, therefore, being compatible with any known polarization mechanism as far as the R p vs. ρ relation is concerned.

A fluorescence-based imaging-fiber electrode chemical sensor for hydrogen peroxide

The fabrication and characterization of imaging fiber electrodes (IFEs) is presented, and the concept of an electrochemically-modulated, fluorescence-based, imaging-fiber electrode chemical sensor (IFECS) is demonstrated. In brief, an imaging fiber distal tip was sputter-coated with a semi-transparent gold layer to create an IFE, and a fluorescent redox dye was immobilized across the IFE face to create an IFECS. An electroactive analyte was imaged by monitoring the change in the immobilized redox dye’s fluorescence following its homogeneous electron transfer reaction with the electroactive analyte. Fluorescence images were collected through the IFECS and detected by an epi-fluorescence microscope/CCD imaging system. Cyclic voltammetry and fluorescence microscopy were utilized to characterize the electrochemical and fluorescence properties of IFECSs. Reversible voltammetry was observed for the rhodamine B isothiocyanate (RBITC) redox couple at IFEs. IFECSs using RBITC as the fluorescent redox dye and Nafion as the immobilization polymer were fabricated to detect hydrogen peroxide. The IFECS’s RBITC-fluorescence was decreased by ∼27% upon exposure to 250 μM hydrogen peroxide and ∼95% of the original fluorescence was observed following the electrochemical regeneration of the Nafion-immobilized RBITC. These IFECSs represent the first union in which remote fluorescence imaging of an electroactive analyte can be performed through the actual fiber-optic electrode itself.

Fundamental studies of ion injection and trapping of electrosprayed ions on a quadrupole ion trap

The quadrupole ion trap is a highly versatile and sensitive analytical mass spectrometer. Because of the advantages offered by the ion trap, there has been intense interest in coupling it to ionization techniques such as electrospray which form ions externally to the ion trap. In this work, simulation and experiment were employed to study the injection of electrosprayed ions into the quadrupole ion trap in a Finnigan MAT LCQ LC/MS n mass spectrometer. SIMION v6.0 was chosen for the simulation studies because it allowed the actual ion trap electrode geometry including endcap holes to be simulated. The endcap holes weaken the rf trapping field in the region near the holes; this distortion of the field is important when ions have large axial excursions as they do in ion injection. In addition, the field penetrates out the endcap holes and affects ions as they approach the ion trap. The results of simulating ions started outside the ion trap agreed well with experimentally obtained ion injection data of the effect of q z during injection. From these simulations, a model for the process by which injected ions are trapped was developed. Injected ions can be trapped even with the modest helium buffer gas pressures commonly used (≈1 mTorr) because ions naturally oscillate for long times (and therefore distances) at certain q z values and initial rf phases. This allows enough collisions to occur to damp the ions’ excess kinetic energy.

Specificity of the kinetics of H2 evolution to the structure of single-crystal Pt surfaces, and the relation between opd and upd H

Abstract It is well known that transition metals exhibit a wide range of catalytic activities for various processes. One of the best examples is the dependence of H 2 evolution kinetics on the nature of the cathode metal. This leads to an expectation that a similar specific dependence would also be observed at various single-crystal surfaces of Pt. In earlier literature this has, however, not been found. In the present paper, it is shown that such conclusions arise from the actual surface-specific electrode kinetics being obscured by effects associated with diffusion of H 2 from a supersaturated region generated near the electrode. By means of Tafel polarization and impedance measurements at several Pt single-crystal surfaces rotated at 3500 rpm, it is shown that there are , in fact, clear specific dependences of the H 2 evolution kinetic parameters on the Pt surface lattice geometry which are related to upd H deposition kinetics and to the well-known surface specificity of the H upd behaviour at Pt as seen in cyclic voltammetry. The question of how the opd H, additional to the upd H, is accommodated at cathodic overpotentials, is addressed.

The influence of impurities on discharge modes and departures to similarity law in for positive polarity

The effect of gaseous impurities such as water vapour and oxygen on the dielectric strength of compressed may be due to either gas composition or electrode surface protrusions. The assumption of a local field enhancement due to protrusions has been rejected due to the actual electrode roughness observed microscopically. It has been shown that the gaseous impurities lead to the creation of initiatory electrons through electron detachment from hydrated negative ions involving water vapour and oxygen, inducing changes in the breakdown regimes. Moreover, without hydration, electrode surfaces are passivated (fluorine deposition) and behave as covered with an insulating layer.

A 3-D SAR model for current source interstitial hyperthermia.

A three-dimensional (3-D) model is presented for the calculation of the specific absorption rate (SAR) in human tissue during current source interstitial hyperthermia. The model is capable of millimeter resolution and can cope with irregular implants in heterogeneous tissue. The SAR distribution is calculated from the electrical potential. The potential distribution is determined by the dielectric properties of the tissue and by the electrode configuration. The dielectric properties and the current injection of the electrodes are represented on a 3-D uniform grid. The calculated potential at an electrode current injection point is not the actual electrode potential at that point. To estimate this potential a grid independent representation of an electrode together with an analytical solution in the neighborhood of the electrode are used. The calculated potential on the electrode surface is used to estimate the electrode impedance. The tissue implementation is validated by comparing calculated distributions with analytical solutions. The electrode implementation is verified by comparing different discretizations of an electrode configuration and by comparing numerically calculated electrode impedances with analytically calculated impedances.

Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at thick-film gold electrodes

Cyclic voltammetric and electrochemical impedance spectroscopic investigations of screen-printed, thick-film gold electrodes reveal significant differences when compared with conventional polished gold disk electrodes of comparable size. The rough and porous structure of the thick-film electrode surface leads to an actual electrode area which is increased six-fold compared to polished disk electrodes. Due to the catalytic properties of these surface structures it is possible to perform the electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) at relatively low overpotentials, i.e. +0.145 V vs. SCE. By operating electrodes at this potential, electrode fouling processes and interference from electroactive species, e.g. acetaminophen, are minimized. An amperometric glucose sensor based on polymer matrix-entrapped glucose dehydrogenase with a working potential of +0.145 V vs. SCE was successfully incorporated into a flow injection analysis (FIA) system.

Multiparticle simulation of ion motion in the ion trap mass spectrometer: Resonant and direct current pulse excitation

A PC-based program that simulates the behavior of a collection of ions is extended to include the effects of collisions with the buffer gas and enhanced visualization methods. The simulations are based on the quadrupole field associated with the actual ion trap electrode structure. Ionization is simulated in such a way as to distribute ionization events randomly over rf phase angles and yield a realistic collection of stored ions. The effects of buffer gas collisions on ion motion during both mass-selective instability and resonance ejection scans are found to include the expected dampening of spatial excursions as well as limitation of the kinetic energy of trapped ions. In both experiments, ion ejection occurs over a number of secular cycles in the vicinity of the theoretical instability point. Activation via a resonant ac signal or a short dc pulse is shown to result in phase-locking of the ions as well as the expected increase in the size of the excursions in the z direction and in ion kinetic energy. Collisions cause dephasing and loss of kinetic energy. Radial dc activation is compared with activation in the axial direction. Experimental data for dc pulse activation of the n-butylbenzene molecular ion are analyzed in phase space and the onset of surface-induced dissociation is correlated with changes in the experimental m/z 91 to m/z 92 fragment ion ratio. Poincaré sections are shown for resonantly excited ions and their value in demonstrating improvement of the resolution of these experiments over conventional mass-selective instability scans is shown.

Steady state solution for electrochemical processes with multiple reacting species

At steady state, the dissociation-association electrochemical reactions in a dilute solution are governed by the nondimensional equations \[ ∂ ∂ x ( d i ∂ u i ∂ x + d i e i ∂ ϕ ∂ x u i ) + R i = 0 , i = 1 , . . . , m , 0 ≤ x ≤ 1 , ∑ i = 1 m e i u i = 0 \frac {\partial }{{\partial x}}\left ( {{d_i}\frac {{\partial {u_i}}}{{\partial x}} + {d_i}{e_i}\frac {{\partial \phi }}{{\partial x}}{u_i}} \right ) + {R_i} = 0, \qquad i = 1,...,m, 0 \le x \le 1, \\ \sum \limits _{i = 1}^m {{e_i}{u_i} = 0} \] where d i , e i {d_i}, {e_i} , and u i {u_i} are the diffusion coefficient, charge, and concentration of the i i th species, respectively. ϕ \phi is the electric potential of the solution. R i {R_i} is the net source of the i i th species in the solution which includes the external input or production due to the reactions in the solution. The extra electroneutrality condition ∑ i = 1 m e i u i = 0 \sum _{i = 1}^m {e_i}{u_i} = 0 determines the electric potential ϕ \phi . This system of nonlinear differential equations is subject to the nonlinear boundary conditions modeling the actual electrode kinetics. We prove the existence of the solution to this system and construct an iterative numerical algorithm to compute the solution. Numerical results are also presented in the paper.

Spatial variations in the charge density of argon discharges in the Gaseous Electronics Conference reference reactor

The spatially dependent ion and electron concentrations of argon discharges in the gaseous electronics conference reference reactor reach a saddle point maximum in the center of the glow. The concentrations were measured using a Langmuir probe. The charge density decreases in the axial direction from the glow center to the electrode sheath edges as expected. In contrast, the charge density increases in the radial direction from the glow center to the radial electrode edge. The maximum occurs approximately 1 cm inside of the actual electrode edge. The most plausible explanation for this increase is enhanced ionization at the electrode edges due to field enhancement there. The electric field is enhanced by the close proximity of the ground shield and driven electrode at the radial edge of the electrode. We estimate that the ionization rate in the plasma near the electrode edge must be almost double of that in the glow center.

Large scale simulation of mass spectra recorded with a quadrupole ion trap mass spectrometer

This paper reports initial results from a study based on a large scale computer simulation of the ion trap mass spectrometer (ITMS). A large number of ions (10 4) are given initial positions and velocities with selected random distributions within the ion trap and a trajectory is calculated for each ion using a new supercomputer ion trap mass spectrometer simulation called numerical quadrupole simulation. Ion velocity and position are computed by numerical integration of the Mathieu equations for a quadrupole field superimposed with a pure dipole term to approximate the electric fields present during resonance ejection. The integration is accomplished via a Taylor series approximation of the solution to the equations of motion. The simulation produces mass spectra which are quantitatively compared with experimental data collected from an ITMS. The actual ITMS electrode geometry was measured as well as the r.f. voltage applied to the ring electrode during mass analysis. Based on these measurements the program was generalized to approximate the quadrupole field created by the non-ideal ITMS electrodes. Good agreement in peak shape and the r.f. voltage of ion ejection is achieved for the molecular ion region of the decapeptide substance P when experimental results are compared with simulations. This is true both in the low and high resolution experiments, the latter being achieved by lowering the rate at which the r.f. voltage is scanned. Data are also given showing that resonant ejection of ions is controlled by the phases of the r.f. and a.c. potentials and that resolution can be improved by choosing the a.c. frequency land initial phase angle with respect to the r.f. phase.

Steady-state solution for electroplating

At steady state, electroplating processes are governed by the dimensionless equations ...(formule)... where d i , e i , and u i are respectively the diffusion coefficient, charge, and concentration of the ith species. The extra electroneutrality condition Σ i=1 n e i u i = 0 will determine the electric potential Φ. This system of nonlinear differential equations is subject to the nonlinear boundary conditions modelling the actual electrode kinetics. The authors prove the existence of the solution and construct a computational algorithm. Numerical experiments are performed on practical data