If we have two different inert metal electrodes, such as Ag and Au, immersed in an aqueous solution, such as NaCl solution (the electrodes cannot dissolve or have redox reactions with the electrolyte), we can definitely still detect a rather stable open circuit voltage over the two electrodes. I am wondering where this potential come from. Is there any method to predict the magnitude of the potential if any other electrodes and electrolytes are selected? Is there any MD simulation to calculate this potential?
It does not matter if the electrodes are inert. If you immerse then in an electrolyte, interfaces will form through the arrangement of superficial charges that lead to the formation of double layers (charge separations that creates a potential) this potential will change according to the electrolyte concentration, Temperature, electrolyte used etc.
I use to call it non faradaic potentials. You could perfom EIS over the open circuit potential and determine capacitance an resistance of the double layer by adjunting to model to a proper equivalent cirtuit. Then by mean of chronoamperometry (in the same potential) integrate te curve an determine de charge related to that double layer. And then with charge.. capacitance and resistance you may calculate te potental related to just one of the varius double layer that may be forming (over the working and counter electrode) the part thay requires more work is to find an equivalent circuit that takes in consideraton al of the double layer to be able to isolate the one you are wanting to evaluate
Sj Li The potential should be the difference between the fermi level of metals but with added electrolyte/temp/metal surface condition there may be some difference. Also, I am not sure if this can be determined in a two-electrode geometry. May be in a 3-electrode geometry, one can think of an experiment where you change the electrolyte concentration, measure EIS (technique/procedure mentioned above by Augusto Rodríguez ) and possibly get an intercept from the extrapolation though I am not sure about the feasibility (i.e if the EIS changes significantly to estimate Capacitance and resistance from circuit analysis). The metal surface/its history will decide the double layer behavior so having ideally a same/pristine surface for all the steps will likely be a necessity.
The cell's voltage (OCV) is, mainly, the difference between the fermi levels (OCV=[E1F-E2F]/qe) of the (non-corroded) metallic electrodes.
The electrolyte (surface 2D, quasi-3D morphology[1], temp., pH, etc.) extra-differences, influences, in practice, the EIS spectra, due to the double layer (extra) ionic-morphology.
1. "The electric double layer describes the remaining distance that has some organization due to the presence of the charged surface.", in: Electric Double Layer https://www.sciencedirect.com/topics/engineering/electric-double-layer
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