NEW APPROACHES TO THE STUDY OF ELECTROCHEMICAL DECARBOXYLATION AND THE KOLBE REACTION: PART I. THE MODEL REACTION WITH FORMATE

1963 ◽  
Vol 41 (1) ◽  
pp. 21-37 ◽  
Author(s):  
B. E. Conway ◽  
M. Dzieciuch
Keyword(s):  
Reaction Mechanisms ◽  
Film Formation ◽  
Open Circuit ◽  
Model Reaction ◽  
Radical Coupling ◽  
Diffusion Controlled ◽  
Reverse Pulse ◽  
Kolbe Reaction ◽  
Current Potential ◽  
Potential Curves

The kinetics of electrochemical decarboxylation of formate ions has been studied in detail for the first time as a model reaction for examination of the decarboxylation and radical coupling that occurs with higher aliphatic acids. Current–potential curves have been obtained which show a sharp transition region, not diffusion controlled, which is characteristic of passivation phenomena. The behavior is observed with gold, palladium, platinum, and gold–palladium alloys. Tafel slopes and exchange currents have been evaluated for the reaction and possible reaction mechanisms are examined in relation to the experimental results.Galvanostatic charging, reverse pulse discharging, and open-circuit decay transients have been obtained which indicate formation of films of adsorbed intermediates on the surface. The transition regions in the current–potential curves are associated with formation of this ad-layer. The galvanostatic results enable distinctions to be made between some of the possible reaction mechanisms proposed and estimates to be made of the extent of film formation by adsorbed intermediates formed in the reaction.

NEW APPROACHES TO THE STUDY OF ELECTROCHEMICAL DECARBOXYLATION AND THE KOLBE REACTION: PART III. QUANTITATIVE ANALYSIS OF DECAY AND DISCHARGE TRANSIENTS AND THE ROLE OF ADSORBED INTERMEDIATES

1963 ◽  
Vol 41 (1) ◽  
pp. 55-67 ◽  
Author(s):  
B. E. Conway ◽  
M. Dzieciuch
Keyword(s):  
Reaction Mechanism ◽  
Anodic Polarization ◽  
Film Growth ◽  
Open Circuit ◽  
Gas Evolution ◽  
Autocatalytic Decomposition ◽  
Kolbe Reaction ◽  
Current Potential ◽  
Potential Curves

Galvanostatic cathodic discharge and open-circuit decay transients have been obtained for the decarboxylation of formate in formic acid and interpreted quantitatively in terms of the adsorption of intermediates in the reaction. These intermediates are identified with HCOO• radicals. Extended anodic polarization at platinum and particularly at palladium leads to the formation of films of an anodic product which are considerably thicker than a monolayer. After relatively long times (> 100 seconds) of anodic polarization, the film growth obeys the inverse logarithmic rate law deduced by Mott and Cabrera. The thick films which are formed at palladium are believed to be responsible, upon autocatalytic decomposition, for the delayed gas evolution phenomenon observed at this metal.A new method for deduction of adsorption pseudocapacitance and charge associated with the ad-layer from open-circuit decay curves and Tafel parameters is used to obtain the pseudo-capacitance and charge associated with the transition region in the current–potential curves for the formate decarboxylation. It is shown that this region corresponds to filling of the surface with adsorbed intermediates formed in the reaction. These observations are shown to support the reaction mechanism proposed in Part I.

scholarly journals Redox mediation at poly(o-aminophenol) coated electrodes: Mechanistic diagnosis from steady state polarization curves

2018 ◽  
Author(s):  
Gabriel Ybarra ◽  
Carlos Moina ◽  
María Inés Florit ◽  
Dionisio Posadas
Keyword(s):  
Steady State ◽  
Polarization Curve ◽  
Experimental Measurements ◽  
Steady State Current ◽  
Thermodynamical Parameters ◽  
Reduction And Oxidation ◽  
Mediated Reduction ◽  
Coated Electrodes ◽  
Current Potential ◽  
Potential Curves

<p class="PaperAbstract"><span lang="EN-US">In this work, the mediated reduction and oxidation of Fe(CN)<sub>6</sub><sup>3-/4-</sup> and Fe<sup>3+ </sup>in poly(o-aminophenol) coated electrodes is analyzed by means of diagnosis diagram based on the features of steady state current-potential curves. This analysis allows to identify the current determining process and to reproduce the experimental characteristics of the polarization curve from the relevant kinetic and thermodynamical parameters with a minimum amount of experimental measurements. </span></p>

scholarly journals The Formation of Sulfide Scales on Carbon Steel in Saturated H2S

2020 ◽  
Author(s):  
Noora Alqahtani ◽  
Jiahui Qi ◽  
Aboubakr M. Abdullah ◽  
Nicholas J. Laycock ◽  
Mary P. Ryan
Keyword(s):  
Carbon Steel ◽  
Corrosion Product ◽  
Film Formation ◽  
Open Circuit ◽  
Iron Surface ◽  
Ion Concentration ◽  
Bulk Solution ◽  
Formation Mechanisms ◽  
Structure Thickness ◽  
Circuit Technique

There are three contributing elements of corrosion of Carbon Steel in H₂ S environment: the effect of H2S on water chemistry; electrochemical reactions of the bare iron surface (both anodic and cathodic processes); and the formation and growth of corrosion product layers. The electrochemical reaction commonly contains three stages: first, the reactant transported from the solution (bulk) to the metal surface; then the transfer of the charge reaction on the surface, followed by the reaction product transported away from the iron surface to the bulk solution or the formation and development of the corrosion product which then can decrease the corrosion rate. Development of a robust corrosion model to predict the corrosion process in H2S requires a mechanistic understanding of all these elements. An experimental study was carried out to assess the corrosion of C-steel under open-circuit technique conditions and in solutions at several ranges of time and temperatures. The effect of film composition, morphology, structure, thickness, and ion- concentration of corrosion product films formed on pipeline Carbon Steel in an acid sour solution were examined. The electrochemical behavior of the filmed steel was measured, and the film properties assessed using a range of advanced techniques including Scanning Electron Microscopy (SEM), and Raman spectroscopy (RS). The data will be discussed in terms of film formation mechanisms.

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