Experiments in Analytical Electrochemistry The Care and Feeding of Electrodes

the actual process is much more complex. Let us imagine that you can sit as an observer on the electrode surface and look out into the solution. What you would see, ignoring for the moment the composition of the electrode surface except to say that it is electrically conductive, is solvent molecules. If the solvent is water, its molecules will appear to be moving in and out, but most will seem to be staying at the surface with a preferred orientation. Besides water, cations or anions of the electrolyte are present and some may be adhering to the surface, competing with the water molecules. Assuming that you also have Ox species in the solution, Ox being less numerous due to its lower concentration may also be observed, albeit less frequently than other components, near the electrode surface. When species stick on the surface, we call it adsorption, and the extent with respect to its bulk concentration, is described by an adsorption isotherm. The amount adsorbed will go to a maximum at monolayer coverage or saturation. If you peer out at a distance beyond a few layers of water, species will be seen to be moving at random except when electrolysis consumes Ox and mass transfer of Ox from the bulk solution occurs to replace the depleted Ox species adjacent to the electrode with R being produced. It in turn diffuses out to the bulk solution where its concentration is zero. It is a very dynamic process.