Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Simulation of a double layer capacitance and a warburg impedance with comsol

  1. May 27, 2010 #1
    Hallo,
    i'm trying to implement a comsol simulation of a impedance spectroscopy experiment.
    But unfortunatly i'm an absolut beginner in Comsol and i have many problems with this work.

    First of all i want to say that i'm using the AC/DC module, more precisely the transient analysis.
    At the moment I'm using a simple 2D geometry to try out all equations and boundary conditions.


    Now to the first problem:
    I tried to simulate only a double layer capacitance between an electrode and a drop of water. The double layer thickness is very small compared to the dimensions of the electrodes, so I didn't want to draw it, but use a distributed impedance for the boundary condition between the electrode and the drop of water.
    The other boundary conditions are:
    Potential V= sin(10*t) on the left side of the electrode.
    Potential V= -sin(10*t) on the right side of the drop of water.
    All other boundaries are electrical insulated.
    But it wasn't sucessfuly, I always recieve the whole potencial difference over the drop of water and not over the distributed impedance.


    The second problem is that I have no idea how to bring the warburg impedance equation into the boundary conditions.
    The equation is something like Z= sigma/sqrt(w)*(1-j), but where do I place that and how can i express w?


    Finaly remains the question, if it is possible to make the simulations automatic over a defined range of frequencies and to calculate a complex impedance out of the result.

    Attachments:
    Comsol1: result, up a simulation with a drawed double layer, down the distributed impedance.
    Comsol2: the boundary condition for the distributed impedance
    Comsol3: the boundary condition of the electrode


    thanke you for your help
    and sorry for my bad english

    cu FirePhoenix
     

    Attached Files:

  2. jcsd
  3. Jul 21, 2010 #2
    Hi!
    I am about to do some simulations of impedance spectroscopy as well. Have you overcome the problems you have mentioned?

    Best regards,
    Mike
     
  4. Jul 21, 2010 #3
    I'm still working on it.

    But at the moment it looks good.

    You have to define the frequency over the scalar variable: nu_emqvw,
    and then define the epsilon_r and the sigma of the doublelayer region as:

    A0_CPE= 1e-6; (use the value of your measurements)
    psi_CPE= 0.5; (0.5 for warburg impedance)

    sigma= (sig_DL+ A0_CPE*(2*pi*frequenz).^psi_CPE*cos(psi_CPE*pi/2));
    epsilon_r= e_DL+ A0_CPE/(epsilon_0)*(2*pi*frequenz).^(psi_CPE-1)*sin(psi_CPE*pi/2);

    lg
    FirePhoenix
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook