F.J. García-García, J. Gil-Rostra, F. Yubero, J.P. Espinós, A.R. González-Elipe, J. Chaboy
Journal of Physical Chemistry C, 119 (2015) 644-652
doi: 10.1021/jp508377v

This work reports a X-ray absorption spectroscopy (XAS) study under “in operando” conditions of the structural and chemical changes undergone by WO₃ and W_xSi_yO_z thin films used as electrochromic cathodes. The electrochromic films were prepared by magnetron sputtering deposition at oblique angles and then characterized by a large variety of techniques. The voltammograms and chronoamperometric diagrams in both aqueous and organic electrolyte media revealed a total reversibility of the electrochromic behavior, a low response time, and a high coloration efficiency for the two types of thin films. The “in operando” X-ray absorption study of the films working in aqueous solutions revealed that when they were electrochemically cycled the average W–O distances reversibly varied by a Δd of 0.06 and 0.08 Å for, respectively, WO₃and W_xSi_yO_z. These changes are discussed by assuming the reduction of W⁶⁺ cations and the transformation of W═O double bonds into single W–O bond structures during the electrochemical cycling of the films.