Rotating Disk Electrode System Research Articles

Highly Active PdPt Catalysts for the Electrochemical Reduction of H2O2

Recent studies have shown that the use of hydrogen peroxide as a fuel cell oxidant instead of oxygen significantly increases the power density. In this paper, we report on highly active carbon supported PdPt catalysts for hydrogen peroxide reduction. Four different PdPt electrocatalysts, Pd/C, Pt/C, Pd0.5Pt0.5/C, and Pd0.25Pt0.75/C, were prepared and characterized using transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and Brunauer–Emmet–Teller surface area analysis. The electrocatalytic activities of these synthesized catalysts were studied using a rotating disk electrode system with a combination of linear sweep voltammetry and chronoamperometry. Our studies show that the Pd0.25Pt0.75/C catalyst has the highest activity for hydrogen peroxide reduction, outperforming the Pd/C, Pt/C, and Pd0.5Pt0.5/C catalysts.

Oxygen reduction activity of N-doped carbon-based films prepared by pulsed laser deposition

Carbon-based films with nitrogen species on their surface were prepared on a glassy carbon (GC) substrate for application as a non-platinum cathode catalyst for polymer electrolyte fuel cells. Cobalt and carbon were deposited in the presence of N 2 gas using a pulsed laser deposition method and then the metal Co was removed by HCl-washing treatment. Oxygen reduction reaction (ORR) activity was electrochemically determined using a rotating disk electrode system in which the film samples on the GC substrate were replaceable. The ORR activity increased with the temperature of the GC substrate during deposition. A carbon-based film prepared at 600 °C in the presence of N 2 at 66.7 Pa showed the highest ORR activity among the tested samples (0.66 V vs. NHE). This film was composed of amorphous carbons doped with pyridine type nitrogen atoms on its surface.

Characteristics of Silver Electrodeposition Solution and Silver Film Fabricated by Electrodeposition with Additives for Interconnection

As the electrodeposition reaction is a heterogeneous reaction including both material transfer and electrochemical reaction, this study tries to find out the reaction mechanism about Ag electrodepostion used as semiconductor interconnection using rotating disk electrode system (RDE system). Considering the environmental problem, non-cyanide Ag electrodeposition solution has been carried out. With varying the process conditions of a certain range including the rotating speed of RDE, applied voltage, and temperature etc., obtained the electrodeposition rate of Ag according to the reaction time. The rate determining step was clarified with the activation energy(Ea) of the electrodeposition reactions for the each process conditions estimated from Arrhenius Plot. Activation energy of Ag in the temperature range between 18°C and 32°C was 3.2kcal/mole. The electrodeposition rate of Ag seems to be controlled mass transport. With the electrodepositon solution mentioned above, the characteristics of silver thin film and bottom-up filling capability were investigated by DC or pulsed electrodeposition method. Especially, the effects of additives on the properties of bottom-up filling of Ag were studied.

Exponentially Expanded Grid Network Approach (EEGNA): An Efficient Way for the Simulation of Electrochemical Problems at Spherical, Cylindrical and Rotating-disk Electrodes

An exponentially expanded space grid technique has been employed in the network simulation of chronoamperometric and voltammetric problems in spherical, cylindrical and rotating-disk electrode systems, leading to an effective simulation strategy for electrochemical problems: exponentially expanded grid network approach (EEGNA). The success of this method is largely due to the improved ability in processing the boundary singularities existing for non-planar diffusions and the enhanced simulation speed and accuracy in contrast to the uniform or quasi-uniform grid network approach.

Mercury detection at boron doped diamond electrodes using a rotating disk technique

Quantification of mercury ions at the ppt level is reported using highly boron-doped diamond (BDD) film electrodes by differential pulse voltammetry (DPV). The DPV experiments were performed in nitrate, thiocyanate and chloride media. Investigation in chloride medium is important since practical samples usually contain chloride impurities. The formation of calomel in a chloride medium on the BDD surface is avoided by the co-deposition of purposely-added gold (3 ppm) during DPV detection. Excellent linear calibration plots have been obtained in all media for ppb ranges. Mercury in the 0.005–50 ppb range has been detected using a rotating disk electrode (RDE) technique in real samples (KCl impinger solutions) prepared from flue gas released by a pilot-scale coal-fired combustion facility. A portable instrument has also been used for the detection of mercury efficiently. These studies have demonstrated that BDD mounted in an RDE system together with gold co-deposition is able to detect mercury with sufficient sensitivity for practical analysis of environmental samples.

Methanol Resistant Cathodic Catalyst for Direct Methanol Fuel Cells

Methanol-tolerant cathodic catalysts were successfully prepared by depositing platinum nanoparticles on heat-treated FeTPP/C [FeTPP stands for 5,10,15,20-tetraphenyl-21H,23H porphine iron(III) chloride] and subsequently sintering the formed catalysts. Different sintering temperatures were investigated to determine its effect on methanol tolerance. Oxygen reduction with/without the presence of methanol on these new catalysts, Pt/C and FeTPP/C, was evaluated by means of potentiodynamic measurement in a rotating disk electrode system. Complete suppression of methanol oxidation while still maintaining high activity towards oxygen reduction was realized on the catalyst sintered at 700°C. Kinetics analysis shows that oxygen reduction on this new catalyst still follows a first-order reaction and has a similar mechanism as that on the pure Pt electrocatalyst. © 2004 The Electrochemical Society. All rights reserved.

Series Solution to the Transient Convective Diffusion Equation for a Rotating Disk Electrode

A series solution to the transient convective diffusion equation for the rotating disc electrode system is presented and compared to previously reported solutions. The solution presented here is for the entire time domain and agrees well with both the short and long time solutions presented earlier in the literature. © 2004 The Electrochemical Society. All rights reserved.

Electrowinning of Platinum Using a Modified Cyclone Reactor

The electrochemical behavior of platinum in dilute acidic media solutions were investigated using a rotating disc electrode system and a modified electrochemical cyclone cell at 25°C. Electrochemical polarization data showed that the limiting current density for platinum deposition was observed around −0.25 V (vs. SCE), and the diffusion coefficient of platinum estimated using Levich equation was 3.25 × 10-6cm2 s-1. The effects of several variables such as applied voltage, hydrochloric acid concentration and electrolyte flow rate were examined using a cyclone cell in order to obtain the optimum condition for electrowinning of platinum. More than 90% of the platinum in solution was recovered within an hour under the optimum conditions.

Electrowinning of palladium using a modified cyclone reactor

The electrochemical behaviour of palladium in dilute acidic chloride solution was investigated using a rotating disc electrode system and the electrowinning of palladium using a modified electrochemical cyclone cell was also carried out. The effect of several variables such as applied voltage, hydrochloric acid concentration and electrolyte flow rate were studied to obtain the optimum conditions for electrowinning. More than 99% of the palladium in solution was recovered within an hour under the optimum conditions using the cyclone cell and grey powdery deposits were observed at a high applied voltage. The purity of palladium electrowon from the leach liquor was at least 99%.

A kinetic study of the cementation of copper from sulphate solutions onto a rotating aluminum disc

The cementation kinetics of copper deposition from sulphate solutions onto aluminum was studied using a rotating disc electrode system. The effect of temperature, Cu ++ ion concentration, rotational speed of the aluminum disc and pH was investigated. The activation energy was found to be 14.1 kJ mol −1, confirming that the rate of reaction was controlled by diffusion.

Direct electron transfer catalysed by recombinant forms of horseradish peroxidase: insight into the mechanism

The paper presents the first results on recombinant horseradish peroxidase (HRP) electrochemistry obtained on graphite with a rotating disk electrode system. Recombinant HRP demonstrates a higher percentage of properly oriented molecules than the native enzyme. The first important conclusion based on the recombinant HRP electrochemistry is that glycosylation hinders direct electron transfer (ET). The single-point mutants with limited activity toward phenolic substrates, viz. Asn70Val and Asn70Asp showed no changes in the registered current upon the addition of p-cresol, catechol, p-aminophenol and guaiacol and, thus, in this particular case mediated ET was not more advantageous than direct ET. The rate constants for direct ET were comparable for all mutants tested in this study demonstrating that direct ET does not depend on the enzyme's ability or inability to oxidise phenolic substrates. The results obtained in this study demonstrate the true mediatorless nature of enzyme-catalysed direct ET.

Electrochemical study on copper cementation from cyanide liquors using zinc

A rotating-disc electrode system was used to study the half-cell reactions involved in the cementation of copper from cyanide liquors onto zinc. Using scanning voltammetry, the reduction of copper cyanide onto glassy carbon and copper discs and the oxidation of zinc from a zinc disc were evaluated at different conditions of solution pH, temperature and free cyanide concentration. Evans diagrams were constructed yielding mechanistic information and rate of the cementation process. Thermodynamic modelling of the copper cyanide system also predicts the electrochemical active species responsible for the reduction of copper cyanide as Cu(CN) 2 −. The study allows optimised conditions to be chosen for the selective recovery of gold from copper–gold cyanide mixture using zinc powder cementation.

Comparison of rotating disk and wall-jet electrode systems for studying the kinetics of direct and mediated electron transfer for horseradish peroxidase on a graphite electrode

Abstract This paper presents a comparison between the results obtained for the kinetics of direct and mediated electroreduction of hydrogen peroxide at horseradish peroxidase (HRP) modified graphite electrodes, used either as a rotating disk electrode (RDE) or as the working electrode in a wall-jet flow through cell. The advantages of using a wall-jet flow system compared with a RDE system for kinetic investigations are that there is no need to account for substrate consumption, especially in the case of desorption of enzyme, and also when studying product-inhibited enzymes. The comparison reveals that identical results can be obtained using either technique. The ratio of HRP molecules on the graphite surface in direct electron transfer contact was determined as 48±4%, and the turnover number of the heterogeneous electron transfer between adsorbed HRP and the graphite electrode was determined as 1.9±0.3 s −1 .

Local current densities in a two rotating disc electrode system with an axial electrolyte inlet measured by an autoradiographic method

The distribution of local current densities in a rotating electrolyser with axial electrolyte inlet in a laminar flow regime was studied by the autoradiographic method. With all systems studied, the local current density decreased monotonically from a maximum value at the inner to a minimum at the outer boundary of the electrode. Experimental results are compared with the numerical solution of the convective diffusion equation by the finite element method.

Transpassive Dissolution of 420 Stainless Steel in Concentrated Acids under Electropolishing Conditions

Anodic dissolution of 420 stainless steel (Fe‐13Cr alloy) in concentrated phosphoric acid, sulfuric acid, and their mixtures has been studied to determine the conditions that lead to electropolishing of the alloy in these electrolytes. A rotating disk electrode system has been employed to study the influence of electrolyte composition, electrode rotation speed, and electrolyte temperature on anodic polarization behavior and the surface finish. Anodic polarization curves in these electrolytes show active‐passive‐transpassive transitions. Concentrated sulfuric acid is found to be unsuitable for electro‐polishing, since metal dissolution is insignificant in this electrolyte, even at very high anode potentials. In phosphoric acid and a mixture of phosphoric and sulfuric acids, electropolishing is observed in the transpassive potential region at or beyond a limiting current plateau. At 90°C, the measured limiting current densities as a function of the rotation speed follow Levich behavior, while at 25°C and 60°C, convective mass transport effects are masked by surface kinetic steps. Highly reflecting and microsmooth surfaces are obtained under conditions where the dissolution reaction is mass transport‐controlled.

Applicability of the Levich Equation for a Two‐Phase Solution in the Rotating Disk Electrode System

AbstractThe mass‐transter characteristics of a two‐phase system formed by mixing a fixed quantity (20 v/v%) of organic solvent with an aqueous ferricyanide electrolyte solution in an RDE system were studied. The Levich eqution, I1 = 0.62 nFACbD2/3v−1/6ω1/2, was found to be applicable to the two‐phase system with only a minor modification in the angular velocity (ω) at Reynolds numbers between 3–5 × 104. The experimental results indicate that the interfacial tension is the most important variable for the two‐phase system. One group of organic solvents with smaller interfacial tension, such as benzene or toluene, needs a modification of the Levich equation by replacing the observed angular velocity (ωo) with the true angular velocity (ωt) which was observed to be 1.1 times the observed angular velocity. For the other group with larger interfacial tension, such as n‐hexane or cyclohexane, there is no need to modify the observed angular velocity. In other words, the Levich equation may be expressed as I1 = 0.65 nFACbD2/3v−1/6ω1/2 for two‐phase solution if the interfacial tension is smaller than 37.0 dyne/cm.

Rigorous Treatment of Rotating Disk Electrode Impedance Data Over the Entire Frequency Range

A rigorous technique of analyzing impedance data for systems which have convective Warburg impedance elements in them has been developed. In particular, a rotating disk electrode system was analyzed, by solving the applicable transient convective diffusion equation numerically. The numerical solution was used to find nonlinear least squares parameters to fit an impedance data set, over the entire frequency range. In this manner the diffusion coefficient and other physical parameters of the system were determined without any assumption about electrode area, solution concentration, or kinetics. The shortcomings of the conventional techniques to evaluate physical parameters from impedance data have been overcome.

Electrodeposition of composition‐modulated alloys in a fluctuating flow field

AbstractThe effect of fluctuating flow on the electrodeposition of binary alloys is analyzed by numerically solving the transient Navier‐Stokes and species continuity equations for a rotating disk electrode system. Timeperiodic modulations of the flow field and the electrode potential are studied and shown to induce periodic deposition rates for a mass‐transfer‐limited species and an activation‐limited species, respectively. Dimensionless groups are formulated to characterize the operating regimes, where composition‐modulated alloys electrodeposit from a single electrolyte and where fluctuating flow influences the composition distribution of the deposit. It is shown that changing the phase angle difference between the flow and potential modulation waveforms can modify the composition gradients in the deposited alloy, whereas other features of the alloy, such as the total composition variation, are affected less by fluctuating flow.

Corrosion of Cu and Cu-Ni Alloys in 0.5M NaCl and in Synthetic Seawater

Abstract Electrochemical corrosion rates of Cu and Cu-Ni alloys have been measured in oxygenated 0.5M NaCl and in synthetic seawater using the Tafel extrapolation procedure. In addition, Cu corrosion has been measured with the linear polarization procedure. A rotating disk electrode system was used in the measurements with rotation rate varying from 500 to 6000 rpm. The corrosion characteristics of Cu and 90Cu-10Ni alloy in the two media, and 70Cu-30Ni alloy in 0.5M NaCl have been found to be similar. For these systems, the variation of corrosion current, corrosion potential, and anodic partial current with rotation rate of the electrode could be explained in terms of a convective diffusion controlled corrosion mechanism incorporating the generation of a soluble copper complex on the electrode surface. The 70-30 alloy in synthetic seawater behaved differently. Corrosion current, corrosion potential, and the anodic partial current were all constant with rotation rate, indicating a surface kinetic-controlle...

Corrosion Behavior of 70Cu-30Ni Alloy in 0.5M NaCl and in Synthetic Seawater

Abstract Electrochemical corrosion rates of 70Cu-30Ni alloy have been measured in oxygenated 0.5M NaCl and in synthetic seawater by the Tafel extrapolation procedure using a rotating disk electrode system. The rotation rate was varied from 500 to 6000 rpm. A log-log plot of the corrosion current vs rotation rate was linear, with a slope of 1/6 for the alloy in 0.5M NaCl; the corrosion potential for the same system became more negative at a rate of approximately −20 mV/dec of rotation. The anodic partial currents at potentials close to the corrosion potential in 0.5M NaCl increased linearly with the square root of the rotation rate. Corrosion current and corrosion potential as well as the anodic partial current for the alloy in synthetic seawater remain unchanged with rotation rate. The anodic Tafel slopes were 60 and 90 mV in 0.5M NaCl and synthetic seawater, respectively. The cathodic Tafel slope was 200 mV for both systems. Two separate corrosion mechanisms for the alloy in two electrolytes have been re...