Abstract
Several electrochemical systems exhibit an intense color change when an electrochemical reaction is induced by an applied electrical field or current. The electrochemical and electro‐optical properties of several such systems have been investigated. These systems are termed electrochemichromic and they can be classified into the following categories: (i) simple redox reaction; (ii) redox reaction coupled with an independent chemical reaction, resulting in variable color persistence; (iii) redox reaction coupled with a chemical reaction producing an insoluble colored species; (iv) redox reaction wherein a solid film deposited on one electrode is reduced and exhibits an intense color change. Analytical models which can describe the electrochemichromic behavior are presented for the different categories.