The use of linear potential sweep voltammetry and of a.c. voltammetry for the study of the surface electrochemical reaction of strongly adsorbed systems and of redox modified electrodes

The use of linear potential sweep (l.p.s.) voltammetry and of a.c. voltammetry for the study of the surface electrochemical reaction of strongly adsorbed systems and of redox modified electrodes is discussed. Ideal l.p.s. or a.c. voltammograms are obtained when there are no interactions between the molecules, the electrode surface is homogenous and the electrochemical reaction is at equilibrium (v/κs or f/κs→0; v=sweep rate; f=frequency; ks=rate of the electrochemical reaction). The l.p.s. peaks are symmetrical and the oxidation and reduction peaks have the same peak potential; in a.c. voltammetry, cotg(=phase angle) is equal to π/2. Interactions between the molecules result in a shift of Ep and in achange of the shape of the curves; in l.p.s. voltammetry the oxidation and reduction peak still have the same peak potentials, and in a.c. voltammetry cotgis still equal to π/2. Heterogeneity of the electrode surface should have effects similar to those observed under certain conditions for interactions between the molecules. When v/ks or f/ks increases, a difference between the l.p.s. oxidation and reduction peaks appears, and in a.c. voltammetry cotgincreases, which allows ks to be calculated. Particular applications to three types of electrodes, modified by irreversible adsorption, by chemical binding and by coating by a polymer are discussed.