Fundamentals of electrochemistry

Abstract

Electrochemistry involves chemical phenomena associated with charge separation, usually in liquid media such as solutions. The charge separation often leads to charge transfer, which can occur homogeneously in solution between different chemical species, 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, the oxidation and reduction half-reactions 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). It is clearly useful to be able to investigate the fundamentals of these electrode processes in the laboratory and this can be done by careful control of the electrode reactions. © Springer-Verlag Berlin Heidelberg 2008.