scholarly journals Super-Nernstian Tafel slopes: An origin in coupled homogeneous kinetics

2020 ◽  
Vol 869 ◽  
pp. 114185 ◽  
Author(s):  
Haotian Chen ◽  
Joseph R. Elliott ◽  
Haonan Le ◽  
Minjun Yang ◽  
Richard G. Compton
Keyword(s):  
Tafel Slopes ◽  
Homogeneous Kinetics

Some Aspects of the Electroreduction of Niazid to Nicotinamide on Mercury Electrodes in Acidic Media

1992 ◽  
Vol 57 (9) ◽  
pp. 1836-1842 ◽  
Author(s):  
Rafael Marín Galvín ◽  
José Miguel Rodríguez Mellado
Keyword(s):  
Electron Transfer ◽  
Essential Role ◽  
Uv Spectroscopy ◽  
Acidic Media ◽  
Polarographic Wave ◽  
Rate Determining Step ◽  
Tafel Slopes ◽  
Reaction Orders ◽  
Mercury Electrodes ◽  
The Waves

The electroreduction of niazid on mercury electrodes has been studied in acidic media (pH < 6). Tafel slopes and reaction orders were obtained at potentials corresponding to the foot of the first polarographic wave. On the basis of both polarographic and voltammetric results it has been shown that the waves appearing at more negative potentials correspond to the reduction of nicotinamide. Protonation of niazid plays an essential role in its reduction and pK values of 1.4, 3.2 and 11.5 were obtained by UV spectroscopy. The process corresponding to the first wave is irreversible, being the second one-electron transfer the rate determining step. Above pH 4 the process is complex due to the overlapping of the waves caused by the occurrence of protonation reactions.

Effect of temperature on cyclic voltammograms during the electrodeposition of lead

1989 ◽  
Vol 67 (1) ◽  
pp. 130-136 ◽  
Author(s):  
Magdy Girgis ◽  
Edward Ghali
Keyword(s):  
Analytical Study ◽  
Ammonium Acetate ◽  
Deposition Process ◽  
Lead Chloride ◽  
Effect Of Temperature ◽  
Cyclic Voltammograms ◽  
Tafel Slopes ◽  
As Adsorption ◽  
And Diffusion ◽  
Potentiostatic Transients

The electrochemical behavior of lead deposition process in a temperature range between 25 and 75 °C was studied in a medium of lead chloride and ammonium acetate by linear and cyclic sweep perturbation. The study was undertaken on four substrates: Pb, Cu, Ag, and C. An increase in temperature resulted in accelerating the deposition process and promoted dendrite formation. Moreover, different kinetic parameters such as adsorption isotherms, Tafel slopes, and diffusion coefficient were affected as a function of temperature elevation. Surface analytical study performed by Auger electron spectroscopy revealed an increase in peak intensities of Cl and Pb as the temperature increased. Keywords: electrodeposition, cyclic voltammetry, potentiostatic transients, underpotential deposition, temperature effect.

scholarly journals Electrochemical Frequency Modulation: New Approach and Revision of Previous Model

2021 ◽  
Author(s):  
Shashi lalvani ◽  
Lei Kerr ◽  
Shamal Lalvani ◽  
Dominic Olaguera-Delogu
Keyword(s):  
Frequency Modulation ◽  
Corrosion Current ◽  
Peak Potential ◽  
New Approach ◽  
Harmonic Currents ◽  
Algebraic Error ◽  
Tafel Slopes ◽  
Incorrect Model ◽  
Original Derivation

Abstract A careful evaluation of the earlier model (1-2) for electrochemical frequency modulation (EFM) involving two sinusoidal applied potentials for the determination of corrosion parameters shows an algebraic error. Although the missing term in the original derivation appears to be insignificant, it is found that errors involved in corrosion current determination, and especially in evaluation of the Tafel slopes can be very significant, which is of consequence because of the rising popularity of this technique. The magnitude of error is found to be a function of the inherent corrosion characteristics (anodic and cathodic Tafel slopes) of the corroding material as well as the applied peak potential of the modulation. A corrected model with detailed steps showing the appropriate math is presented. In addition, using the experimental data available in the literature, the errors involved in estimating the corrosion parameters by the earlier EFM model of Bosch et al (1-2) are evaluated. The corrected corrosion current and the Tafel slopes can be recovered from the incorrect model without the benefit of the harmonic currents, as shown in this paper.The analysis is also presented for the case of only one applied sinusoidal frequency modulation, which offers several advantages over the multiple frequency modulation.

scholarly journals Understanding the reaction mechanism of Kolbe electrolysis on Pt anodes

2021 ◽  
Author(s):  
Sihang Liu ◽  
Nitish Govindarajan ◽  
Hector Prats ◽  
Karen Chan
Keyword(s):  
Reaction Mechanism ◽  
Potential Range ◽  
Microkinetic Model ◽  
Rate Determining Step ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Tafel Slopes ◽  
Kolbe Electrolysis ◽  
Kolbe Reaction ◽  
Rate Limiting

Kolbe electrolysis has been proposed an efficient electrooxidation process to synthesize (un)symmetrical dimers from biomass-based carboxylic acids. However, the reaction mechanism of Kolbe electrolysis remains controversial. In this work, we develop a DFT- based microkinetic model to study the reaction mechanism of Kolbe electrolysis of acetic acid (CH3COOH) on both pristine and partially oxidized Pt anodes. We show that the shift in the rate-determining step of oxygen evolution reaction (OER) on Pt(111)@α-PtO2 surface from OH* formation to H2O adsorption gives rise to the large Tafel slopes, i.e., the inflection zones, observed at high anodic potentials in experiments on Pt anodes. The activity passivation as a result of the inflection zone is further exacerbated in the presence of Kolbe species (i.e., CH3COO* and CH3*). Our simulations find the CH3COO* decarboxylation and CH3* dimerization steps determine the activity of Kolbe reaction during inflection zone. In contrast to the Pt(111)@α-PtO2 surface, Pt(111) shows no activity towards Kolbe products as the CH3COO* decarboxylation step is limiting throughout the considered potential range. This work resolves major controversies in the mechanistic analyses of Kolbe electrolysis on Pt anodes: the origin of the inflection zone, and the identity of the rate limiting step.

scholarly journals Corrosion Performance of AISI-309 Exposed to Molten Salts V2O5-Na2SO4at 700°C Applying EIS andRpElectrochemical Techniques

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
E. F. Diaz ◽  
C. Cuevas-Arteaga ◽  
N. Flores-García ◽  
S. Mejía Sintillo ◽  
O. Sotelo-Mazón
Keyword(s):  
Molten Salts ◽  
Electrochemical Impedance ◽  
Electrochemical Techniques ◽  
Metallic Surface ◽  
Corrosion Performance ◽  
Potentiodynamic Polarization Curve ◽  
Linear Polarization Resistance ◽  
Second Stage ◽  
Tafel Slopes ◽  
Bode Plots

The corrosion performance of AISI-309 exposed 5 days to molten salts 50 mol% V2O5-50 mol% Na2SO4at 700°C is reported in this paper. Such evaluation was made using three electrochemical techniques: potentiodynamic polarization curve (PC), electrochemical impedance spectroscopy (EIS), and linear polarization resistance (Rp). FromPC, the Tafel slopes,Icorr, andEcorrwere obtained. From Nyquist and Bode plots, it was possible to determine two different stages; the first one showed just one loop, which indicated the initial formation of Cr2O3layer over the metallic surface; after that, the dissolution of Cr2O3formed a porous layer, which became part of the corrosion products; at the same time a NiO layer combined with sulfur was forming, which was suggested as the second stage, represented by two capacitive loops. EIS plots were in agreement with the physical characterization made from SEM and EDS analyses. Fitting of EIS experimental data allowed us to propose two electrical circuits, being in concordance with the corrosion stages. Parameters obtained from the simulation of EIS data are also reported. From the results, it was stated that AISI-309 suffered intergranular corrosion due to the presence of sulfur, which diffused to the metallic surface through a porous Cr2O3layer.

scholarly journals The transition from inhomogeneous to homogeneous kinetics in CO binding to myoglobin

1994 ◽  
Vol 66 (5) ◽  
pp. 1612-1622 ◽  
Author(s):  
N. Agmon ◽  
W. Doster ◽  
F. Post
Keyword(s):  
Homogeneous Kinetics
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