Preparation of Ni Oxyhydroxide Thin Films by Reactive Sputtering in H_2O Atmosphere and Their Electrochromic Properties

摘要

Electrochromic (EC) materials change their optical properties (darken and lighten) with the application of a low reversal voltage (1). An EC device generally consists of an ion-conducting layer sandwiched between an EC layer, an ion storage layer, and two transparent electrodes. Tungsten oxide (WO3) is the most typical EC material, which colors by reduction and bleaches by oxidation. Ni oxide is used as ion storage and second EC layer, which colors by oxidation and bleaches by reduction. Electrochemical reaction between Ni hydroxide [Ni(OH)_2] and Ni oxyhydroxide [NiOOH] is proposed for the EC mechanism of Ni oxide. Because it is difficult to prepare Ni(OH)_2 or NiOOH thin films by dry processes, such as sputtering and pulsed laser deposition, NiO thin films have been prepared at first and then electrochemically converted to Ni(OH)_2 or NiOOH in electrolyte solutions (2-4).