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Forum index » Science and Technology » Chem » Electrochem
Faradaic Impedance
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Yan
science forum beginner


Joined: 10 Mar 2005
Posts: 5

PostPosted: Wed Oct 26, 2005 4:23 am    Post subject: Faradaic Impedance Reply with quote
When simulating AC voltammograms (absolute admittance vs. DC potential)
one should account for a spherosymmetrical diffusion (in case of a
spherical electrode) by placing a resistance with a value
r0*(sigma)i*(2/Di)^.5 in parallel with the Warburg impedance of species
i (Electroanalytical Chemistry, a series of advances, vol.4. Marcel
Dekker, N.Y., 1970. p.53). I was wondering how the value of this
resistance would change for a hemispherical electrode, and, in general,
for any sub- or superhemispherical microelectrode.

Thanks a lot!
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beav
science forum addict


Joined: 18 Oct 2005
Posts: 63

PostPosted: Wed Oct 26, 2005 5:44 pm    Post subject: Re: Faradaic Impedance Reply with quote
On 25 Oct 2005 21:23:25 -0700, "Yan" <aliaks666@tut.by> wrote:

Quote:
When simulating AC voltammograms (absolute admittance vs. DC potential)
one should account for a spherosymmetrical diffusion (in case of a
spherical electrode) by placing a resistance with a value
r0*(sigma)i*(2/Di)^.5 in parallel with the Warburg impedance of species
i (Electroanalytical Chemistry, a series of advances, vol.4. Marcel
Dekker, N.Y., 1970. p.53). I was wondering how the value of this
resistance would change for a hemispherical electrode, and, in general,
for any sub- or superhemispherical microelectrode.

Thanks a lot!


i'm really digging deep into the memory on this one, but wouldn't this
have been addressed during the development of polarography in the
1940's or 1950's?

i'm sorry that i can't give you an answer, but i do recall this
question being raised and the development of the dropping mercury
electrode as a means to factor it out....
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Yan
science forum beginner


Joined: 10 Mar 2005
Posts: 5

PostPosted: Wed Oct 26, 2005 7:22 pm    Post subject: Re: Faradaic Impedance Reply with quote
Quote:

i'm really digging deep into the memory on this one, but wouldn't this
have been addressed during the development of polarography in the
1940's or 1950's?

i'm sorry that i can't give you an answer, but i do recall this
question being raised and the development of the dropping mercury
electrode as a means to factor it out....

You are probably right. Gerischer (1951) was the one who solved it for
a spherical electrode. But I am having troubles getting anything in
case of a hemispherical electrode...
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Dieter Britz
science forum beginner


Joined: 04 May 2005
Posts: 45

PostPosted: Thu Oct 27, 2005 7:36 am    Post subject: Re: Faradaic Impedance Reply with quote
beav wrote:
Quote:
On 25 Oct 2005 21:23:25 -0700, "Yan" <aliaks666@tut.by> wrote:


When simulating AC voltammograms (absolute admittance vs. DC potential)
one should account for a spherosymmetrical diffusion (in case of a
spherical electrode) by placing a resistance with a value
r0*(sigma)i*(2/Di)^.5 in parallel with the Warburg impedance of species
i (Electroanalytical Chemistry, a series of advances, vol.4. Marcel
Dekker, N.Y., 1970. p.53). I was wondering how the value of this
resistance would change for a hemispherical electrode, and, in general,
for any sub- or superhemispherical microelectrode.

Thanks a lot!



i'm really digging deep into the memory on this one, but wouldn't this
have been addressed during the development of polarography in the
1940's or 1950's?

i'm sorry that i can't give you an answer, but i do recall this
question being raised and the development of the dropping mercury
electrode as a means to factor it out....


The resistance to a hemisphere, if it is sitting on an insulating
plane, is half that to a whole sphere. Flattened or bulging shapes
are more complicated, and are of interest in these days of ultramicro
electrodes. Check papers by Oldham and coworkers for the last 20 years
or so, also Amatore.

--
Dieter Britz, Kemisk Institut, Aarhus Universitet, Danmark.
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Yan
science forum beginner


Joined: 10 Mar 2005
Posts: 5

PostPosted: Fri Oct 28, 2005 4:30 am    Post subject: Re: Faradaic Impedance Reply with quote
Quote:
The resistance to a hemisphere, if it is sitting on an insulating
plane, is half that to a whole sphere. Flattened or bulging shapes
are more complicated, and are of interest in these days of ultramicro
electrodes. Check papers by Oldham and coworkers for the last 20 years
or so, also Amatore.

--
Dieter Britz, Kemisk Institut, Aarhus Universitet, Danmark.



Thank you Dr. Britz, I appreciate your help.
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