Kinetics Of Electrochemical Oxidation Research Articles

Kinetics of the electrochemical oxidation of organic compounds at BDD anodes: modelling of surface reactions

This paper presents the results of a numerical study of the kinetics of electrochemical oxidation of different organic substances at boron doped diamond (BDD).

Electrochemical oxidation kinetics and mechanism of ethylene glycol on a carbon supported Pt catalyst: A quantitative DEMS study

The effect of external parameters such as the reaction potential, reactant concentration, catalyst loading and, in potentiodynamic measurements, the scan rate, on the kinetics and mechanism of ethylene glycol (EG) oxidation on carbon supported Pt catalyst, specifically on the Faradaic current and the selectivity for CO2 formation (CO2 current efficiency), was examined and quantified by electrochemical and differential electrochemical mass spectroscopy (DEMS) measurements under continuous flow conditions. The dependence of the Faradaic current and the CO2 current efficiency on these parameters can be understood in terms of a complex reaction network, where successive oxidation of the –OH functional groups leads to a sequence of partial reaction products with intact C–C bond, such as glycol aldehyde, glycolic acid, etc., which continue to react or desorb from the catalyst as by-products on the one hand, while C–C bond rupture in any of these adsorption/oxidation steps, during EG adsorption/oxidation or during readsorption/oxidation of any of the partial oxidation products, results in the formation of adsorbed CO and CO2 as total oxidation product. For all potentials, EG concentrations, and catalyst loadings investigated the current efficiencies of CO2 are below 25%; under relevant steady-state conditions they are in the range of a few percent, reflecting the high barrier for C–C bond breaking under current reaction conditions.

Electrochemical Oxidation of Am(III) and Am(V) Ions in HNO3 Solutions Containing Potassium Phosphotungstate K10P2W17O61

The kinetics of electrochemical oxidation of Am(III) and Am(V) on Pt electrode in solutions of concentrated nitric acid containing potassium phosphotungstate was studied spectrophotometrically. The processes occurring in the system follow the rate law for reversible reaction. The direct reaction is first-order with respect to the concentration of Am(III) ions, and the reverse process is a zero-order reaction.

The effect of methanol and ethanol cross-over on the performance of PtRu/C-based anode DAFCs

In the present work, the cross-over rates of methanol and ethanol, respectively, through Nafion®-115 membranes at different temperatures and different concentrations have been measured and compared. The changes of Nafion®-115 membrane porosity in the presence of methanol or ethanol aqueous solutions were also determined by weighing vacuum-dried and alcohol solution-equilibrated membranes. The techniques of anode polarization and adsorption stripping voltammetry were applied to compare the electrochemical activity and adsorption ability, respectively. To investigate the consequences of methanol and ethanol permeation from the anode to the cathode on the performance of direct alcohol fuel cells (DAFCs), single DAFC tests, with methanol or ethanol as the fuel, have been carried out and the corresponding anode and cathode polarizations versus dynamic hydrogen electrode (DHE) were also performed. The effect of alcohol concentration on the performance of PtRu/C anode-based DAFCs was investigated.It was found that ethanol shows lower cross-over rates than methanol through the Nafion® membrane in spite of the higher membrane porosity resulted in presence of ethanol aqueous solutions. Furthermore, it was found that ethanol presents less negative effect on the cathode performance due to both its smaller permeability through Nafion® membrane and its slower electrochemical oxidation kinetics over Pt/C cathode.

Electrochemical Oxidation of Am(V) Ions in HNO3Solutions

Oxidation potentials (E0p) of the Am(VI)/Am(V) couple were measured and the kinetics of electrochemical oxidation of Am(V) on platinum electrode in concentrated solutions of nitric acid (1-7 M) containing potassium phosphotungstate K10P2W17O61 (KPW) was studied by the potentiometric method with spectrophotometric control of the oxidation states. The potential E0p is independent of the concentrations of HNO3 and KPW and is shifted toward the negative region by 70 mV (ΔE0p) as compared to 1 M HClO4. The extent of Am(V) oxidation into Am(VI) under the experimental conditions studied remains almost constant and comprises ≈90%. Electrochemical oxidation of Am(V) is described by the kinetic equation of the first and zero orders with respect to the Am(V) concentration: -dCAm(V)/dt = k'1CAm(V) - k'0.

Kinetic Study on the Removal of Organic Pollutants by an Electrochemical Oxidation Process

This paper deals with the kinetics of electrochemical oxidation of 2,6-dichlorophenol and p-hydroxybenzoic acid in phosphate buffer at pH = 7. On the basis of experimental results, a mathematical model was formulated which effectively describes the trend in time of the concentration of the organic compounds involved in the electrochemical oxidation process. The proposed kinetic model is based on a reaction mechanism which takes into account both the direct oxidation of the organic substrate at the electrode surface and the indirect oxidation, in the liquid phase, by means of electrogenerated oxidizing agents. The model well interprets the complex effect on the removal efficiency of such operating parameters as the current density, the linear velocity of the electrolyte, and the ratio between the anode surface and solution volume.

Electrochemical Oxidation of Am(III) Ions in HNO3 Solutions

Formal oxidation potentials (E0p) of the Am(IV)/Am(III) couple were measured and the kinetics of electrochemical oxidation of Am(III) on platinum electrode in concentrated solutions of nitric acid (1-6 M) containing potassium phosphotungstate K10P2W17O61 (KPW) was studied. The formal potential E0p only slightly depends on the concentration of HNO3 and is shifted toward the negative region by ≈1.0 V as compared with the standard values. The extent of Am(III) oxidation increases with increasing KPW concentration and decreasing concentration of nitric acid. Electrochemical oxidation of Am(III) is accompanied by radiochemical reduction of Am(IV) and is described by the equation -dCAm(III)/dt = (k + k1)CAm(III) - k1C0 - k0, where k is the apparent rate constant of electrochemical oxidation of Am(III), k1 is the apparent rate constant of Am(IV) reduction, and k0 is the constant of radiation-chemical reduction of Am(IV).

Kinetics of electrochemical oxidation of ammonia in alkaline solution

The kinetics of the anodic oxidation of ammonia in alkaline solutions at platinized platinum has been investigated by the galvanostatic method. The galvanostatic charging curves show three polarization levels. Times of transition between the second and third level are independent of ammonia concentration, as are also the exchange current densities, and the standard current densities at −300 mV(she) for the first and the second levels respectively. The second level showed Tafel behaviour with slopes of 40. The nature of the rest potential is discussed and some remarks about possible reaction mechanisms are made. It is suggested that the rest potential is a reversible hydrogen potential determined, by the atomic hydrogen produced by the chemical decomposition of ammonia at the electrode. It is also shown that no mechanism suggested in the literature can be accepted without further investigation. Raney nickel was also tested but meaningful results were not obtained.