Large cation model of dissociative reduction of electrochromic WO3−x films

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AbstractStudies of dissociative reduction processes of electrochromic WO3−x films were conducted to: (i) evaluate their utility for electroetching and (ii) determine their fundamental mechanistic features to reduce or eliminate their occurrence in normal optical switching and modulation operation of WO3−x films. We have found that while the small intercalating cations stabilize WO3−x structure, the large nonintercalating surfactant cations (Et4N+, CtMe3N+) contribute to the dissociative reduction. While these cations do not affect WO3−x structure of anodically protected films (E > 0.2 V), they cause surface lattice polarization on electron injection to the conduction band of WO3−x at lower electrode potentials, in the absence of intercalating cations. We have found that this process is limited to the surface and no structural damage occurs to the underlying film. The mechanistic aspects of the process have been discussed on the basis of experimental voltammetric and electrochemical quartz crystal nanogravimetric (EQCN) measurements and ab initio quantum mechanical calculations.