Fundamentals of Electrochemistry

Abstract

Electrochemistry involves chemical phenomena associated with charge separation, usually in liquid media. The charge separation often leads to charge transfer, which can occur homogeneously in solution, or heterogeneously on electrode surfaces. In order to ensure electroneutrality, two or more charge transfer half-reactions take place simultaneously, in opposing directions: oxidations (loss of electrons or increase in oxidation state) and reductions (gain of electrons or decrease in oxidation state). In the case of heterogeneous redox reactions, these are separated in space, usually occurring at different electrodes immersed in solution in a cell. The electrodes are linked by conducting paths both in solution (via ionic transport) and externally (via electric wires etc.) so that charge can be transported and the electrical circuit completed. If the cell configuration permits, the products of the two electrode reactions can be separated. When the sum of the free energy changes at both electrodes is negative the electrical energy released can be harnessed (batteries, fuel cells). If it is positive, external electrical energy can be supplied to overcome the positive free energy and oblige electrode reactions to take place and convert chemical substances (electrolysis).