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Galvanic Cell with same reaction for the anode and for the cathode

Posted 18 mag 2018, 16:10 GMT-4 Battery Design, Electrochemistry 1 Reply

Robert Rubio
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How to model a galvanic cell that has the same reaction for the anode and for the cathode? We have a Galvanic Cell with only two species Ox (oxidized species) and Red (reduced specie) and these species react as follow:

*cathode: Ox + e = Red E= 0 V
* anode: Red = Ox + e E= -90mV

The different potential could be due to the temperature difference between the cathode and the anode. If the initial concentration for Ox and Red are the same and regardless the fast kinetic for the anode (anode has a major temperature that cathode). It is supposed that these concentrations are invariant with the time, because one specie is consumed in one electrode and is produced in the other electrode. I am trying to solve this, but the system do not reach the steady state. The species change their concentration with the time. Does anyone know why? Thank you, for your time

In Comsol, I first solve for the convection problem with the Laminar Flow and Heat transfer in Fluids physics. Then, I solve the Tertiary Current Distribution with Butler-Volmer concentration dependence. I attached some images of my model al results.

1 Reply Last Post 21 mag 2018, 01:58 GMT-4
Lasse Murtomäki
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Posted: 7 years ago 21 mag 2018, 01:58 GMT-4

Non-isothermal cells are tricky. Due to the temperature gradient in the system, thermodiffusion takes place which polarizes the concentrations, otherwise you would not see any cell voltage. Sure, the sum of Ox and Red must remain constant. We just published a paper about impedance spectroscopy in a thin cell with temperature gradient. Calculus in it is rather awful, but you can read the very first pages where establishing the equilibrium is described. See https://doi.org/10.1016/j.jelechem.2018.04.054

I am not sure if Comsol has a ready-made module for this problem, you'll probably have to define your own equations.

Lasse

Non-isothermal cells are tricky. Due to the temperature gradient in the system, thermodiffusion takes place which polarizes the concentrations, otherwise you would not see any cell voltage. Sure, the sum of Ox and Red must remain constant. We just published a paper about impedance spectroscopy in a thin cell with temperature gradient. Calculus in it is rather awful, but you can read the very first pages where establishing the equilibrium is described. See https://doi.org/10.1016/j.jelechem.2018.04.054 I am not sure if Comsol has a ready-made module for this problem, you'll probably have to define your own equations. Lasse

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