The Electrified Interface

Abstract

In the last chapter, we focused on the equilibrium potential developed by an electrochemical cell. We relied on thermodynamics and paid no attention to the molecular details. We shall now look more closely at the interface between an electrode and an electrolyte solution. Virtually any surface in contact with an electrolyte solution acquires a charge and therefore an electric potential different from that of the bulk solution. There are four ways in which a surface may acquire a charge: (1) imposition of a potential difference from an external potential source; (2) adsorption of ions on a solid surface or on the surface of a colloidal particle; (3) electron transfer between a metallic conductor and the solution; and (4) for micelles, biological macromolecules and membranes, ionization of functional groups such as carboxylate, phosphate, or amino groups. Surface charge effects are particularly important in biological systems. The surface-to-volume ratio of a biological cell is large and most biochemical reactions occur at or near the surface of an immobilized enzyme.