Numerical Analysis of the Steady-State Behavior of CE Processes in Rotating Disk Electrode Systems

Leal, Pedro Henrique Moura; Leite, N. A.; Viana, Pedro Rupf Pereira; Sousa, Flávio V.V. de; Barcia, Oswaldo E.; Mattos, O.R.

doi:10.1149/2.0501809jes

Cited by 7 publications

(8 citation statements)

References 16 publications

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“…The other boundary ( x = δ) has to be defined as a distance at which activities are assumed to be constant values in the bulk solution. Empirically, it is assigned to be three times of the highest the Levich diffusion layer thickness (δ Levich, i ). ,, The Levich diffusion layer thickness is given by …”

Section: Methodsmentioning

confidence: 99%

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Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H₂ and Buffer Ions

2019

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Although the electrochemical hydrogen evolution reaction (HER) on a Pt electrode is among the most studied electrocatalytic reactions, its reaction mechanism and exchange current density are still under debate. Particularly on the Pt catalyst, its facile reaction kinetics and lack of effective methods to compensate mass transport make it difficult to isolate kinetic and diffusion contributions. This study focuses on the quantitative description of mass transfer constraints arising from both H 2 and phosphate buffer ions using a Pt electrocatalyst in near-neutral pH regions, which are overlooked in the literature despite the relevance to various (photo-) electrochemical reactions for water splitting and CO 2 reduction. The established HER model that uses H + as a reactant quantitatively breaks down the observed overpotentials with diffusion contributions of both hydrogen and buffer species while the intrinsic kinetics on Pt exhibits negligible contribution. The significance of electrolyte engineering, that is, the optimization of the electrolyte identity and molality, is confirmed to determine the overall HER performance. To maximize the HER performance on Pt at ambient temperature, the phosphate-buffer electrolyte should be adjusted to a pH close to pK a of the buffer that effectively minimizes the pH gradient and to the adequate molality of the buffer (typically ∼0.5 M phosphates) that H 2 diffusion is maximized, which is related with H 2 solubility and solution viscosity. At pH far from pK a , concentration overpotential of buffer ion dominates the overall performance, which requires highly dense buffer (>1.5 M phosphates) to minimize the pH gradient.

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Section: Methodsmentioning

confidence: 99%

“…Empirically, it is assigned to be three times of the highest the Levich diffusion layer thickness (δ Levich,i ). 25,32,33 The Levich diffusion layer thickness is given by…”

Section: ■ Introductionmentioning

confidence: 99%

Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H₂ and Buffer Ions

2019

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“…Previous work with the RDE and a preceding chemical reaction [27,28] typically considered cases with =1 and/or excess of ligand (first order reaction).…”

Section: Relationships For the Ligands Profilesmentioning

confidence: 99%

Full wave analysis of stripping chronopotentiometry at scanned deposition potential (SSCP): Obtaining binding curves in labile heterogeneous macromolecular systems for any metal-to-ligand ratio

Pinheiro

Galceran

Rotureau

et al. 2020

Journal of Electroanalytical Chemistry

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The different deposition potentials applied in Scanned Stripping ChronoPotentiometry (SSCP) probe different values of the free metal and complex concentrations at the electrode surface. The knowledge of these concentrations gives access to a relevant window of the binding curve of a metal to a homogeneous or heterogeneous ligand. Here, a suitable mathematical treatment for the determination of these surface concentrations, when using a mercury thin film rotating disk electrode, is reported. The proposed procedure does not require ligand excess conditions and takes advantage of the knowledge of the free metal ion concentration in the bulk solution provided by the technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). It is experimentally shown that the information derived from the SSCP points (i.e. at different deposition potentials in a unique solution) is consistent with the speciation results yielded by the technique AGNES in pertinent solutions prepared within a range of metal-to-ligand ratios. Successful examples with polystyrene sulfonate, Laurentian Fulvic acid and a peat humic acid are reported. It is concluded that, by running consecutively SSCP and AGNES in a single solution, speciation information corresponding to different compositions (i.e. those locally generated at the electrode JELECHEM-D-20-00386 second_revision.docx 30/06/20 2/35 surface by the end of the deposition step) can be retrieved, this enabling an easy determination of the binding curve.

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“…1,2 Since then, researchers have used these equations either to extract experimental parameters (e.g., reaction rates of the chemical step) 3 or even to detect the presence of a preceding chemical step. 4,5 Besides the restrictions imposed by the reaction layer hypothesis, all these approaches involve exclusively steady-state techniques, 6 which has kept motivating research groups to develop new theoretical and numerical procedures to study the transient response of these systems. [7][8][9][10][11][12][13] Among the different transient techniques that can complement these results, impedance methods stand out for their ability to characterize the system under a linear regime, greatly simplifying the mathematical treatment.…”

Section: List Of Symbolsmentioning

confidence: 99%

“…In a previous article, we have already addressed the steady-state behavior of CE mechanisms in RDE systems. 6 Now, our main goal is to extend the analysis to their transient responses, focusing on diffusion and EHD impedances. Contributions are mainly centered in the systematic approach to understanding how different parameters affect both Z D and Z EHD .…”

Section: Abmentioning

confidence: 99%

Numerical Analysis of CE Processes in RDE Systems: Diffusion and Electro-hydrodynamic Impedances

Leal

Barcia

Mattos

2020

J. Electrochem. Soc.

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This paper presents a numerical analysis of the effect of different parameters (rotation speed, equilibrium constant and Schmidt numbers) on the diffusion (ZD) and electro-hydrodynamic (ZEHD) impedances of chemical-electrochemical (CE) systems in a rotating disk electrode (RDE) configuration. For this purpose, we used a finite difference algorithm to discretize and solve the governing equations. Our results show that the separation between convection-diffusion and reaction impedance loops depends on the ratio between diffusion layer thickness ( δ N ) and reaction layer thickness ( δ R ). Also, we have demonstrated that the characteristic frequency of the reaction impedance loop is a function of δ R − 2 . As for ZEHD data, we found that, for slow kinetics, the plots do not overlap for different rotation speeds. Further, the upper limit of the negative phase is different for both, slow and fast kinetics, from the usual 180° value found for single charge transfer systems. The increment of the equilibrium constant, obtained via increasing the reaction rate constant of the electroactive species, caused the magnitude ZD to decrease and that of ZEHD to increase. Lastly, we found that changing ScA mainly affects the concentration gradient at the surface while the effect of ScB will depend on the kinetic regime.

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Numerical Analysis of the Steady-State Behavior of CE Processes in Rotating Disk Electrode Systems

Cited by 7 publications

References 16 publications

Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H₂ and Buffer Ions

Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H₂ and Buffer Ions

Full wave analysis of stripping chronopotentiometry at scanned deposition potential (SSCP): Obtaining binding curves in labile heterogeneous macromolecular systems for any metal-to-ligand ratio

Numerical Analysis of CE Processes in RDE Systems: Diffusion and Electro-hydrodynamic Impedances

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Numerical Analysis of the Steady-State Behavior of CE Processes in Rotating Disk Electrode Systems

Cited by 7 publications

References 16 publications

Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H2 and Buffer Ions

Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H2 and Buffer Ions

Full wave analysis of stripping chronopotentiometry at scanned deposition potential (SSCP): Obtaining binding curves in labile heterogeneous macromolecular systems for any metal-to-ligand ratio

Numerical Analysis of CE Processes in RDE Systems: Diffusion and Electro-hydrodynamic Impedances

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Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H₂ and Buffer Ions

Maximizing Hydrogen Evolution Performance on Pt in Buffered Solutions: Mass Transfer Constrains of H₂ and Buffer Ions