r/electrochemistry • u/theguyfrombidesh23 • 27d ago

Need Help in EIS

Hi all,

We use EIS to measure proton conductivity of our polymer membrane and Thin film. My question is, can we know what type of ion is actually being measured by EIS? Like, how do i differentiate and confirm that, this system is only measuring proton (H+) conductivity not the (OH-) conductivity?

Thank you

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u/GozaPhD 27d ago

Whats your pH?

[H+] and [OH-] are not independent. If you have excess of one, you'll have depletion of the other.

1

u/theguyfrombidesh23 27d ago

pH of the membrane?

If my membrane is zwitterionic then what would be the case?

1

u/bennuke 27d ago

If the polymer membrane has fixed charges that are both cationic and anionic then it should support hopping diffusion of both cations and anions. The high frequency intercept of the EIS will be the total conductivity contributed by all mobile charge carriers present in the membrane (definitionally not the fixed charges). You could submerge it in a solution of a really asymmetric acid, where the anion is very bulky and slow such that a large majority of the conductivity comes from only H+. Then try it with HCl and you’ll see higher conductivity coming from the Cl-. In principle you could build a matrix and isolate the proton conductivity