I wonder why we need to use Ag/AgCl electrodes. Can we use some metal like aluminum , copper or chrome instead? Are there special characteristics of these electrodes for biomedical applications? Obviously, the quality of signal will be degraded with other metals electrodes but is it still acceptable?
Quick and dirty answer: In order to transfer a charge from an electrode in a solution, you have to switch from electronic current (in the metal) to an ionic current in the solution (or vice versa). Problem is, that the solution tries to "shield" the charged metal surface by (depending on the detailed look) at least the Helmholtz-Double layer of ions. That means, a metal in solution not only forms a an electrical half-cell, but a capacitor as well. Now, usually one could life with that issue, since the surrogate circuit only acts like a filter for signals, but depending on the "noble-ness" (the half-cell potential) of the metal, it is prone to corrosion, too. That means, with less noble metals, you are depositing metal ions in the body, which is not acceptable. Electrodes forming the capacitance by Helmholtz-Layer are called "polarizable".
A Ag/AgCl electrode transfers the charge across its boundaries by a reversible Redox-Reaction. It is thus not forming a double layer and has thus "no" filter properties.... It is called non-polarizable electrode.
There is a lot more to it, but I hope it suffices for the moment.
Does anybody know who was the initiator of use of Ag/AgCl electrodes in biomedical application and what was exactly the original motivation?
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