Rotating Ring Disk Electrode Experiments Research Articles

Detection of Intermediate during Electrochemical Polymerization of Azure A and X‐ray Photoelectron Spectroscopy of Poly(azure A)

The electrochemical polymerization of azure A has been investigated by the rotating ring‐disk electrode (RRDE) and the X‐ray photoelectron spectroscopy (XPS). The electrolysis of azure A was studied in the pH region of 1.0 and 12.0. The results from the RRDE experiments show that the electrochemical polymerization of azure A was performed by two steps, i.e., oxidation of azure A and followed by polymerization. The intermediates generated at the disk were detected at the ring electrode in the ring potential region of −0.2–0.20 V (vs. Ag/AgCl reference electrode). The collection efficiencies of the intermediates increase with decreasing the ring potential as well as increasing the rotation rate of the RRDE. Thus, the intermediate is to carry a positive charge species and not too stable. The results from the XPS experiments show that the anions can be doped into poly(azure A) film and be dedoped from it during oxidation and reduction processes.

Comparison of Voltammetric Responses over the Cathodic Region in LiPF6 and LiBETI with and without HF

This study reports the effects of HF on the voltammetric responses below (vs. ) in solutions being widely used in rechargeable lithium-ion batteries (LIBs). During the first cathodic scan on a Pt electrode, two reduction peaks are observed between 3.0 and in solutions irrespective of the solvents used. The reduction reactions are absent in LiBETI solutions but present after the addition of trace amount of HF. Thus, the reduction reactions in solutions are due to the HF, an inevitable impurity of solutions. Based on the results of the rotating disk electrode and the rotating ring disk electrode experiments, two reduction peaks are assigned to the hydrogen underpotential deposition and the hydrogen evolution reaction, respectively. HF reduction reactions forms a surface layer of which the main constituent is LiF. The surface layer suppresses the other reduction reactions otherwise occurring below . For example, the electrodeposition of metallic Mn, which takes place below in LiBETI solutions, is severely hampered in solutions. The passivity by HF reduction is observed not only for a Pt electrode but also for a glassy carbon electrode.

Oxygen reduction reaction in acid medium at iron phthalocyanine dispersed on high surface area carbon substrate: tolerance to methanol, stability and kinetics

The electrocatalytic performance of iron phthalocyanine, FePc, dispersed on a high surface area carbon substrate (Vulcan XC 72) was investigated in acid medium. The polarisation curve of oxygen reduction on the FePc/C catalyst in a methanol containing O 2-saturated electrolyte was compared to that obtained on a platinum catalyst. Results showed clearly that FePc/C catalyst is totally insensitive to the presence of methanol and becomes a better catalyst than the Pt/C catalyst for the oxidation reduction reaction (orr) at low overpotentials, indicating that FePc/C catalyst is a good alternative to platinum based catalysts as a cathode catalyst for low working temperatures fuel cells. The major problem of this catalyst in acid medium is its poor long-term stability, which was demonstrated by electrochemical measurements and characterized by in situ infrared reflectance spectroscopy experiments. The infrared spectra showed that FePc degradation occurred via the substitution of the central metal of the macrocycle by two protons, leading to the formation of a free base phthalocyanine which is known to be inactive for oxygen reduction catalysis. From this observation, it was possible to improve the FePc stability by using a gas diffusion electrode. Under these conditions, oxygen reduction was performed on a FePc/C electrode for at least 24 h with a constant current density of −25 mA cm −2 at room temperature. Finally, cyclic voltammetry experiments at different electrode rotation rates Ω led to determine the Koutecký-Levich plots from which it was shown that the kinetic parameters for the orr at FePc/C electrodes are similar to those obtained at platinum particles. The total number of exchanged electrons n t during the orr on the FePc/C catalyst was determined by rotating ring disc electrode experiments leading to n t close to 3.9–4.

Anodic oxide growth on tungsten studied by EQCM, EIS and AES

Anodic oxide growth on tungsten in 0.1 M H 2SO 4 + 0.4 M Na 2SO 4 has been studied on stationary and rotating electrodes using the electrochemical quartz crystal microbalance (EQCM), Auger electron spectroscopy (AES) depth profiling, electrochemical impedance spectroscopy (EIS) and the rotating ring disc electrode (RRDE). The sputter rate of tungsten oxide was calibrated with respect to a tantalum oxide reference film using Rutherford backscattering spectroscopy (RBS). Long time polarisation experiments at constant potential showed that at a stationary electrode the oxide thickness determined by AES increased with time, whereas a steady state was reached after a few seconds under rotating conditions. On the other hand, EIS indicated a time independent oxide thickness on both stationary and rotating electrodes. Both methods yielded a higher absolute thickness for stationary electrodes. The oxide growth behaviour at short times was studied with the EQCM by monitoring the current and the mass change resulting from a potential step. From these data the film growth fraction and the oxide thickness change were calculated. After an initial period of a few seconds dominated by film growth, the rotating electrodes exhibited a significant mass loss contrary to stationary electrodes. RRDE experiments confirmed dissolution during anodic polarisation of a rotating electrode. The results of this study demonstrate the necessity to combine several experimental methods when studying anodic film growth and they illustrate the usefulness of the EQCM which can monitor directly and with sub-second time resolution the mass change of the electrode together with the current density. They show the decisive effect of convection conditions on anodic oxide growth on tungsten.

Structural effects during CO adsorption on Pt–bimetallic surfaces: I. The Pt(100) electrode

Synchrotron surface X-ray scattering (SXS) and rotating ring disk electrode (RRDE) measurements have been performed during the coadsorption of metal adatoms and carbon monoxide on the Pt(100) surface in an electrochemical environment. Whereas RRDE experiments give a macroscopic view of the coadsorption process, via the adsorption isotherms of deposited metal adatoms, the SXS measurements give insight into the structural changes that occur on the atomic level. The results show that both underpotentially deposited (UPD) Cu and Pb are displaced by CO from the Pt(100) surface, the driving force being the resulting negative shift in the surface free energy. When bromide is present in a c(2×2) structure on top of the Cu monolayer there is an activation barrier to the displacement effect. Coadsorption of CO then enhances the c(2×2) structure by displacing disordered Cu or Br that is present on the surface. Cycling the electrode potential, during which the Cu monolayer is desorbed, leads to complete blocking of the UPD process by CO. In contrast to these results, the reversible formation of a Bi c(2×2) UPD adlayer is unaffected by the presence of solution CO.

Polycrystalline gold electrode redox behavior in an ammoniacal electrolyte

Abstract The underpotential deposition (upd) of copper at polycrystalline gold in an ammoniacal electrolyte (0.1 M NH 3 +0.1 M NaClO 4 ) was investigated. The rotating ring disk electrode (RRDE), the electrochemical quartz crystal microbalance (EQCM) and time of flight secondary ion mass spectrometry (TOF-SIMS) were all used in parallel to study this process. RRDE experiments showed that upd of Cu(0) occurred at −0.4 V E

Electrochemistry of Conductive Polymers: XX. Early Stages of Aniline Polymerization Studied by Spectroelectrochemical and Rotating Ring Disk Electrode Techniques

Early stages of aniline oxidation have been studied employing spectroelectrochemical and rotating ring disk electrode experiments in solutions of low (2 mM) and high (100 mM) aniline concentrations in . Results indicate that a large amount of the tail‐to‐tail dimer, benzidine, is produced in the initial stage of aniline oxidation, which is followed by the generation of the head‐to‐tail dimer, N‐phenyl‐p‐phenylene diamine (PPD), as well as oligomers in solutions of high aniline concentrations. The intermediate species have been identified by spectroelectrochemical and rotating ring disk electrode (RRDE) voltammetry experiments, and the relative amount of dimeric products has been estimated from the RRDE voltammograms. Evidence for the presence of a nascent species produced upon oxidation of aniline is presented from the RRDE experiments.

The effect of high LiCl concentrations upon the competition between anodic decomposition and stabilization of the n-GaAs/Fe 2+ electrode

The competition between the anodic decomposition of the GaAs electrode and the stabilization of this electrode by ferrous ions has been studied by rotating ring—disc electrode experiments in aqueous electrolytes in the presence and absence of 4 M LiCl. The addition of 4 M LiCI appears to lead to a marked improvement of the stabilization and to a change in competition mechanism. These effects can be explained by a model in which it is assumed that the decomposition and stabilization mechanisms are controlled by the relative concentrations of the different surface decomposition intermediates. On adding 4 M LiCl the water activity is decreased, so that shifts occur in the equilibria determining the concentrations of various decomposition intermediates, leading to changes in the competition kinetics at the surface of the GaAs/Fe 2+ electrode. Surface composition data obtained by X-ray photoelectron spectroscopy measurements after current flow are discussed.

Electrochemical characterization of carbohydrate oxidation at copper electrodes

The electrochemical oxidation of carbohydrates at copper electrodes in alkaline solution is studied by cyclic voltammetric and rotating ring-disk electrode experiments. It is demonstrated herein that an important step in the oxidation of carbohydrates is their interaction with the oxide/hydroxide layer covering the electrode. This interaction is believed to involve the Cu(I) oxidation state although interaction with Cu(II) may also occur once it is formed. The extent of this interaction is measured by the decrease in peak height and electrochemical charge under the Cu(II) formation wave, and is sugar dependent. It is interesting that there is a correspondence between the extent of the interaction and the oxidative charge measured between 0.4 and 0.6 V (Ag/AgCl reference electrode) in the presence of carbohydrates. Structural effects may be influencing the interaction between carbohydrates and the electrode surface. The oxidation of many carbohydrates occurs in the potential region corresponding to the formation of Cu(III). Rotating ring disk electrode experiments strongly suggest that Cu(III) plays an important role in carbohydrate oxidation after the adsorption step. The electrooxidation of glucose at copper electrodes in alkaline solutions goes beyond the formation of gluconic acid (two electron transfer). Further oxidation may continue through CC bond cleavage. A mechanism for the oxidation of carbohydrates at copper electrodes is proposed. The mechanism includes the formation of complex species between the carbohydrates and the copper.

Voltammetric measurement of bimolecular electron-transfer rates in low ionic strength solutions

Abstract : Electrochemical investigations of homogenous chemical reactions that are coupled to an initial electron-transfer step are frequently based on methods in which the mass-transfer coefficient of a reactant or intermediate is experimentally varied relative to the inherent rate of the chemical reaction. Common methods employed in studying coupled chemical reactions include the rotating disk electrode (RDE), rotating ring-disk electrode (RRDE), and cyclic voltammetry. In the RDE and RRDE experiments, the rate of mass-transfer is proportional to the square-root of the electrode rotation rate so that the mass- transfer rate may be adjusted to a value comparable to the rate of the chemical reaction. The dependence of the limiting current in this experimental regime may be analyzed, using appropriate kinetic equations, to determine the rate constant of a chemical reaction.