Discrimination of Inner- and Outer-Sphere Electrode Reactions by Cyclic Voltammetry Experiments

A laboratory experiment for undergraduate students who are studying homogeneous and heterogeneous electron-transfer reactions is described. Heterogeneous or electrode reaction kinetics can be examined by using the electrochemical reduction of three Fe-III/Fe-II redox couples at platinum and glassy carbon disk electrodes. Cyclic voltammetric measurement is suitable for determining the electrode-reaction rate constants. The dependence of the rate constant on the electrode materials enables the students to discriminate and discuss the mechanism of the electrode reaction. The experiment is completed in a 5-h laboratory period for pairs of students in analytical chemistry lab class. This material is also suitable for an inorganic chemistry lab class.