3.1 INTRODUCTION

All electrochemical reactions and phenomena occur in a medium, usually a solvent containing dissolved ions (often called the supporting electrolyte or just the electrolyte) which are mobile and able to support current flow. The properties of this medium (which we will call the solvent electrolyte combination, or sometimes the electrolyte for short) are critically important to any electrochemical experiment. A medium containing mobile ions must exist between the electrodes in an electrochemical cell to allow for control and/or measurement of the electrode potential in the cell, which is required in nearly all electrochemical experiments. A medium with good solvating power is needed to dissolve reactants and products from the electrode reaction, and one with reasonably low viscosity is often needed to allow for rapid transport of reactants and products to and from electrodes. Finally, a medium with low reactivity, or at least with a specific desired reactivity, is needed that will be compatible with oxidizing and reducing electrodes and with reactive species which might be created at electrodes, for any of a wide variety of reasons including analysis, synthesis, energy conversion, or simply the novelty of making a new species for the first time and studying its properties.

This chapter will focus on the properties of some solvent electrolyte combinations that are commonly used in electrochemical science. Many excellent reviews exist on the properties of solvents and solvent electrolyte combinations for use as media for performing electrochemical experiments (1 5) and we will not attempt to present a comprehensive review...