Introduction

This chapter introduces the basic elements of the electrochemistry encompassing the redox processes that are the main subject of this monograph. Section 3.2 describes the fundamentals, starting with the origin of the cell emf (the electric potential across it), introducing the use of electrode potentials, and their determination in equilibrium conditions within simple electrochemical cells. In the first example (with electroactive species that resemble type-I electrochromes), the reactants are all ions in solution. In the second example, the cell assembly comprises two electrodes, each a metal in contact with a solution of its own ions, somewhat resembling type-II electrochromes. Though electrochromic electrodes are intrinsically more complicated than the two examples cited here, they follow just the principles established. Details of fabrication for electrochromic devices (ECDs) appear in Chapter 14. Section 3.3 exemplifies the kinetic features underlying electrochromic coloration. In it, the rates of mass transport and those of electron transfer, the three rate-limiting (thus current-limiting) processes encountered during the electrochemistry, are described. Diffusion of both electrochrome and counter ions is discussed more fully in Chapter 5, to illustrate the way charge-carrier movement limits the rate of the coloration/bleaching redox processes within ECDs.

Section 3.4 covers electrochemical methods involving dynamic electrochemistry, particularly cyclic voltammetry, which is important in studying electrochromism; three-electrode systems are required here.

More comprehensive treatments of electrochemical theory will be found elsewhere.