Interpretation of Isopotential Points The Common Intersection in Families of Current-Potential Curves

A commnn intersection point can occur in a family of current-potential curves at an electrode provided the potential scanning program is the same for all curves, the electrode surface is partially covered with at least one adsorbed or deposited species at the start of the application of the potential program, the initial amount of the adsorbed or deposited species is different for each curve, and the electrode surface behaves as if it consists of two independent electrochemical regions the sum of whose aress is constant at all times for all of the current-potential curves. The mathematics interpreting the origin of isopotential points is analogous to that for isosbestic points in spectrophotometry, but must be suitably modified to take into account the nonequilibrium electrochemical situation. The experimental systems studied were oxidation of adsorbed SO₂ on platinum, oxidation and reduction of a heterogeneous gold-platinum surface, oxidation of thin copper films on platinum, and oxidation of a platinum electrode with both absorbed SO₂ and I^-. Some literature examples of isopotential points are discussed, and the validity of the theory is confirmed by a comparison of conclusions with those reached by other techniques.