Energies of Activation of Electrode Reactions: A Revisited Problem

Šepa, D. B.

doi:10.1007/978-1-4613-0327-5_1

Cited by 4 publications

(8 citation statements)

References 142 publications

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“…[7][8][9] Recalling that, in electrochemistry, the activation energy is also a function of an electrical variable such as the cell voltage measured respect to a reference electrode, the potential difference through the interface between the working electrode and the electrolytic solution (Galvani potential) or the overpotential of the overall electrochemical reaction. 10 The choice of one of these variables determines the linear scale that governs the dependence of the activation energy with the chosen electric variable. In this manuscript, the and will be consider as a function of the potential difference for numerical convenience, and the obtained results are independent of the electric variable itself.…”

Section: Introductionmentioning

confidence: 99%

Apparent Activation Energy in Electrochemical Multistep Reactions: A Description via Sensitivities and Degrees of Rate Control

2020

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Activation energy is a well-known empirical parameter in chemical kinetics that characterizes the dependence of the chemical rate coefficients on the temperature and provides information to compare the intrinsic activity of the catalysts. However, the determination and interpretation of the apparent activation energy in multistep reactions is not an easy task. For this purpose, the concept of degree of rate control is convenient, which comprises a mathematical approach for analyzing reaction mechanisms and chemical kinetics. Although this concept has been used in catalysis, it has not yet been applied in electrocatalytic systems, whose ability to control the potential across the solid/liquid interface is the main difference with heterogenous catalysis, and the electrical current is commonly used as a measure of the reaction rate. Herein we use the definition of 'degree of rate control for elementary step' to address some of the drawbacks that frequently arise with interpreting apparent activation energy as a measure of intrinsic electrocatalytic activity of electrode. For this, an electrokinetic model Langmuir-Hinshelwood-like is used for making numerical experiments and verifying the proposed ideas. The results show that to improve the catalytic activity of an electrode material, it must act upon the reaction steps with the highest normalized absolute values of degree of rate control. On the other hand, experiments at different applied voltages showed that if the electroactive surface poisoning process take place, changes in can not be used to compare the catalytic activity of the electrodes. Finally, the importance of making measurements at steady-state to avoid large errors in the calculations of apparent activation energy is also discussed.

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Section: Introductionmentioning

confidence: 99%

Apparent Activation Energy in Electrochemical Multistep Reactions: A Description via Sensitivities and Degrees of Rate Control

2020

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“…E a,±m is the electrochemical activation energy defined as a function of ϕ, which is equivalent to the electrochemical Gibbs energy of activation. 58 2.2. Electrokinetic Model for the FAEOR.…”

Section: Methodsmentioning

confidence: 99%

“…Meanwhile, this electrical state depends on the direction of the reaction as well as the scale and value of the potential used to control it. 58 For numerical convenience, we calculated the activation energies using a scale based on ϕ, as it was originally defined. 66 Just as the kinetic model allows us to access the electrode potential, it is also possible to obtain the rate coefficients involved in each reaction step proposed in eqs r 1 −r 7 .…”

Section: T T T T T T T T T T T T T T T Tmentioning

confidence: 99%

Thorough Analysis of the Effect of Temperature on the Electro-Oxidation of Formic Acid

et al. 2020

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In this work, the effect of temperature on the electro-oxidation of formic acid on platinum was modeled and numerically investigated. Numerical simulations were carried out using an electrokinetic model recently validated through voltammetric and galvanostatic experiments. We show that the intrinsic electrocatalytic activity of the working electrode for the overall electrochemical reaction can hardly be interpreted from the apparent activation energy due to the complexity of the reaction scheme. A detailed analysis is possible through the estimation of the activation energies determined from the individual rate coefficients. By doing so, we observed that the direct pathway, with an activation energy of 91 kJ mol–1 at 0.40 V and 72 kJ mol–1 at 0.80 V, is the energetically easiest pathway for the formation of CO2 in the proposed reaction scheme. Regarding the self-organized potential oscillations under the galvanostatic regime, our model was able to reproduce experimentally observed results including the phenomena of temperature compensation and overcompensation. Importantly, we have introduced a formalism to classify the elementary steps that contribute to the increase and decrease of the oscillatory frequency in electrochemical systems. Our results shed light on the understanding of the temperature dependence of complex electrocatalytic reactions, and the developed methodology was proven to be robust and of general applicability.

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“…[7][8][9] Recalling that, in electrochemistry, the activation energy is also a function of an electrical variable such as the cell voltage 𝑈 measured respect to a reference electrode, the potential difference 𝜙 through the interface between the working electrode and the electrolytic solution (Galvani potential) or the overpotential 𝜂 of the overall electrochemical reaction. 10 The choice of one of these variables determines the linear scale that governs the dependence of the activation energy with the chosen electric variable. In this manuscript, the 𝐸 𝑎 and 𝐸 𝑎𝑝𝑝 will be consider as a function of the potential difference 𝜙 for numerical convenience, and the obtained results are independent of the electric variable itself.…”

Section: Introductionmentioning

confidence: 99%

Apparent Activation Energy in Electrochemical Multistep Reactions: A Description via Degrees of Rate Control

Calderón-Cárdenas¹,

Paredes-Salazar²,

Varela

2020

Preprint

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<div> <div> <div> <p>Activation energy is a well-known empirical parameter in chemical kinetics that characterises the dependence of the chemical rate coefficients on the temperature and provides information to compare the intrinsic activity of the catalysts. However, the determination and interpretation of the apparent activation energy in multistep reactions is not an easy task. For this purpose, the concept of degree of rate control is convenient, which comprises a mathematical approach for analyzing reaction mechanisms and chemical kinetics. Although this concept has been used in catalysis, it has not yet been applied in electrocatalytic systems, whose ability to control the potential across the solid/liquid interface is the main difference with heterogenous catalysis, and the electrical current is commonly used as a measure of the reaction rate. Herein we use the definition of ‘degree of rate control for elementary step’ to address some of the drawbacks that frequently arise with interpreting apparent activation energy as a measure of intrinsic electrocatalytic activity of electrode. For this, an electrokinetic model Langmuir-Hinshelwood-like is used for making numerical experiments and verifying the proposed ideas. The results show that to improve the catalytic activity of an electrode material, it must act upon the reaction steps with the highest normalised absolute values of degree of rate control. On the other hand, experiments at different applied voltages showed that if the electroactive surface poisoning process take place, changes in 𝐸𝑎𝑝𝑝 can not be used to compare the catalytic activity of the electrodes. Finally, the importance of making measurements at steady-state to avoid large errors in the calculations of apparent activation energy is also discussed. </p> </div> </div> </div>

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Energies of Activation of Electrode Reactions: A Revisited Problem

Cited by 4 publications

References 142 publications

Apparent Activation Energy in Electrochemical Multistep Reactions: A Description via Sensitivities and Degrees of Rate Control

Apparent Activation Energy in Electrochemical Multistep Reactions: A Description via Sensitivities and Degrees of Rate Control

Thorough Analysis of the Effect of Temperature on the Electro-Oxidation of Formic Acid

Apparent Activation Energy in Electrochemical Multistep Reactions: A Description via Degrees of Rate Control

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