I have a simple question about electrochemical double layer (ECDL). If we apply a potential (+ 0.5 V) to a carbon electrode in water + NaCl
and then remove it (open circuit) why does the potential decreases with time (self discharge) and does not stay at 0.5V ? For me we have created an ECDL, thus the potential should be thus stable with time. In this open circuit configuration, where go the electrons from the carbon electrode ? Faradaic reactions ? which ones ? thank you
Dear Mickael Pruvost ,
When you apply a potential, the thermodynamic equilibrium at the interface electrode/solution is displaced, and when you remove it a new equilibrium need to be established at the interface electrode/solution.
If your are right about that the potential should be stable at 0.5 V (which I think is not true), so this means that your ECDL is not stable.
Please let me know if you find a final answer to your question.
You observe capacitive charging and (instant auto)discharging of your carbon electrode. ECDL is not stable if a Nernst (redox) equilibrium is not involved. ECDL exists in solution and it is an effect of the potential appearance, not its cause: no (externally applied) potential, no ECDL.
The involved charge is very,very low. The concept of potential is more related with the energy and less with the electron quantity (charge). All electrons are there before and after the experiment.
Dear Mickael Pruvost,
what is your cell (RE[1], CE, WE[2]) ?
Could you show, please, the potential over time ?
PS: A time series of some G-EIS (at open circuit phase, iDC=0, iAC=1uA) measurements[3], using an equivalent circuit modeling[4], then you might resolve[4] your question(s)[5].
1. you note potential, not Voltage.
2. what is your carbon electrode ?
3. EIS: Potentiostatic or Galvanostatic Mode? https://www.gamry.com/application-notes/EIS/eis-potentiostatic-galvanostatic-mode/ ; https://www.bio-logic.net/wp-content/uploads/part-i-basics.pdf
4. http://egmont.com.pl/gamry/noty/EIS%20Primer%202006.pdf ; https://ocw.mit.edu/courses/chemical-engineering/10-626-electrochemical-energy-systems-spring-2014/lecture-notes/MIT10_626S14_S11lec06.pdf ;
https://www.fhi-berlin.mpg.de/acnew/department/pages/teaching/pages/teaching__wintersemester__2012_2013/cornelia_breitkopf__impedance_spectroscopy__121207.pdf
5. where go the electrons from the carbon electrode ? Faradaic reactions ? which ones ?
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