The Ion-Storage Capacity and Surface Characterization of Ce/Cu Thin Films

Irena Kozjek Škofic,a Janez Kovačb and Nataša Bukoveca*

a Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana, Slovenia
b Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
* Corresponding author: E-mail:

Ce/Cu mixed oxide thin films with molar ratio 1 were prepared by sol-gel method and dip-coated on SnO2/F covered glass. The cyclic voltammetry and chronocoulometry were carried out to determine their suitability for application as a counter-electrode in electrochromic devices. The charge capacity is up to 20 mC cm–2, however, the reversibility of the redox process decreases with the number of cycles. Surface composition and chemical bonding of elements on the surface of the cycled and non-cycled part of the Ce/Cu mixed oxide thin film were investigated by X-Ray photoemission spectroscopy (XPS) and surface morphology was analyzed by atomic force microscopy (AFM). The Cu atoms on the non-cycled surface are bonded as Cu(2+), whereas after cycling the Cu atoms are reduced to Cu(1+). The Ce atoms in both areas are in the Ce(4+) state. The Ce/Cu ratio measured by XPS on the surface of the non-cycled area is higher than on the surface of the cycled one. In the cycled area the Li is present, bonded in thin film as Li2CO3.

Keywords: Ce/Cu mixed oxide thin film, counter-electrode, sol-gel process, XPS, AFM