Working Modes of Electrochemical Systems

In this article we describe all the possible working modes of electrochemical systems. In galvanic cells, a spontaneous chemical reaction is used to produce electrical work. In electrolytic cells, an applied voltage more positive than the cell potential forces a current through the cell and produces a chemical reaction that would not otherwise occur. A less explored behavior of electrochemical cells involves the application of an external voltage with the occurrence of a spontaneous chemical reaction. The current flow has the same direction as in a galvanic cell resulting in an increase in the spontaneous reaction rate; therefore, we call this mode a “driven cell.” Current-versus-voltage curves determined in the well-known Daniell cell and the practical examples discussed in this paper are relevant for the comparison of this working mode with those normally presented to the students. Thermodynamic characterization and sign conventions complete the description and promote the proper integration of concepts associated to electrochemical systems.