Electrode Potential Measurements

Abstract

How does one actually measure the potential difference between an electrode and electrolyte, so far only theoretically discussed? A potential-measuring device (voltmeter) has two input terminals. The measuring electrode can be connected with one terminal, but how can one “shunt off” the potential inside the electrolyte solution to the other terminal of the device? There is no other alternative but to immerse a second conductor in the test solution as a “shunt” electrode and connect it to the second input terminal of the voltmeter. However, at this newly formed phase boundary (“shunt” electrode/test solution) the same physical and chemical phenomena arise (orientation, charge separation, charge transfer) as those at the working electrode, whose individual, absolute magnitude one actually wishes to measure. At this second interface we get an additional Galvani potential Δ ΦR. What we read off of the voltmeter is then the sum of several Galvani potentials. A set-up of this type -two electrodes in a common electrolyte — is called an electrochemical cell; similarly, one electrode constitutes an electrochemical half-cell.