Electrochromic Behavior of Nickel Oxide Electrodes: I . Identification of the Colored State Using Quartz Crystal Microbalance

In the present paper the quartz crystal microbalance is used as a sensitive detector of mass changes taking place during an electrochromic process. Electrochemical and electrochromic characteristics of nickel oxide electrodes strongly depend on the preparation method of the samples. Three different types of materials are studied and their electrogravimetric responses compared: hydroxide film prepared by cathodic deposition from a Ni 2+ ‐containing solution; porous and stoichiometric nickel oxide films formed by anodic oxdation of a nickel electrode in a concentrated solution; and nonstoichiometric films prepared by electron‐beam evaporation. A formula describing the colored film is proposed, taking into account the effect of hydrated alkaline cation (Li + ; K + ) incorporation.