Electrochemical characterization of optically passive CeVO4 counterelectrodes

Ceria-vanadia stoichiometric oxides represent a new class of optically pass ive counterelectrodes with favorable properties for the use as counterelect rodes in an electrochromic window. They are very transparent both in the pr istine state and in the lithium-intercalated condition and have a good char ge capacity (around 20 mC cm(-2)). In the present paper we report on the el ectrochemical properties of Ceria-Vanadia stoichiometric oxides, in liquid PC-LiClO4 anhydrous electrolytes. The cyclic voltammograms of such electrod es show reversible reduction/oxidation peaks in two distinct regions, aroun d 1.2-2.2 V vs. Li and 2.9-3.9 V vs. Li. GITT experiments have been perform ed, with the following results: Li diffusion coefficient goes from 10(-10) for pristine samples down to 10(-13) cm(2) s(-1) for fully intercalated sam ples. The impedance of Ceria-vanadia is that of a ceramic thin film, going from a slightly p-type semiconducting state to a more insulating sample wit h resistivity of 0.1 G Omega cm when fully Li-intercalated. The optical properties of the samples are that of a colorless, very transpa rent electrode (T>88% in the wavelength range between 450 and 740 nm). Extr emely weak cathodic and anodic electrochromism can be detected in the red a nd in the violet part of the visible spectrum, respectively. This extremely low absorption is of no harm to the visible appearance of the samples. (C) 1999 Elsevier Science Ltd. All rights reserved.