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Limiting current from Rotating Disk Electrode - Simulation doesn't match theory
Posted 19 août 2015, 17:37 UTC−4 Computational Fluid Dynamics (CFD), Electrochemistry, Modeling Tools & Definitions, Parameters, Variables, & Functions, Studies & Solvers Version 5.1 2 Replies
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I am having an problem getting a value for the current at an electrode, that is being rotated in solution, that would be expected from theory.
The Levich equation ( en.wikipedia.org/wiki/Levich_equation ) models the diffusion and solution flow conditions around a Rotating disk electrode (RDE). The Levich equation gives the height of the sigmoidal wave observed in rotating disk voltammetry, or the limiting current. The limiting current can be approached, for example, by increasing the electric potential or decreasing the rate of mass transfer to the electrode. The RDE reduces the rate of mass transfer through induced flux and is equivalent to a silent solution at steady state.
I began with model library. I found the microdisk volatmmetry model. This model shows the limiting current as the applied potential is changed.
The Levich equation ( en.wikipedia.org/wiki/Levich_equation ) models the diffusion and solution flow conditions around a Rotating disk electrode (RDE). The Levich equation gives the height of the sigmoidal wave observed in rotating disk voltammetry, or the limiting current. The limiting current can be approached, for example, by increasing the electric potential or decreasing the rate of mass transfer to the electrode. The RDE reduces the rate of mass transfer through induced flux and is equivalent to a silent solution at steady state.
I began with model library. I found the microdisk volatmmetry model. This model shows the limiting current as the applied potential is changed.
2 Replies Last Post 24 août 2015, 14:53 UTC−4
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Posted:
9 years ago
Hi
I have also tried to model a rotating disk electrode and reproduce Levich equation. I neither managed to reach the expected behaviour, i.e. limiting current depending on the square root of the rate of rotation. Only at very low rates of f = 1...3 Hz (w = 2*pi*f) I had a satisfactory but not an accurate correspondence. Meshing is the key point in electrochemical simulations because current is proportional to the concentration gradient at the surface, and numerical gradients are always inaccurate.
I think that my simulations coud be improved if I increased the simulation domain much bigger. I probably see now the effect of the domain boundaries, although I had them similar to the measurement conditions.
Hence, my message is: You have probably done everything all right, but fluid dynamics is very difficult to simulate. Therefore, specific CFD software packages are used in chemical engineering, but I am not an expert on them.
BR
Lasse
I have also tried to model a rotating disk electrode and reproduce Levich equation. I neither managed to reach the expected behaviour, i.e. limiting current depending on the square root of the rate of rotation. Only at very low rates of f = 1...3 Hz (w = 2*pi*f) I had a satisfactory but not an accurate correspondence. Meshing is the key point in electrochemical simulations because current is proportional to the concentration gradient at the surface, and numerical gradients are always inaccurate.
I think that my simulations coud be improved if I increased the simulation domain much bigger. I probably see now the effect of the domain boundaries, although I had them similar to the measurement conditions.
Hence, my message is: You have probably done everything all right, but fluid dynamics is very difficult to simulate. Therefore, specific CFD software packages are used in chemical engineering, but I am not an expert on them.
BR
Lasse
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Posted:
9 years ago
Thanks! Im glad I am not the only one with this issues.
And the COMSOL support has been both helpful and not helpful at the same time. They do answer a lot of questions but have no solution or explanation for why their software cannot match these analytical solutions.
That is why I decided to ask the forum. Thanks for the response.
And the COMSOL support has been both helpful and not helpful at the same time. They do answer a lot of questions but have no solution or explanation for why their software cannot match these analytical solutions.
That is why I decided to ask the forum. Thanks for the response.