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

Abstract

Studies of dissociative reduction processes of electrochromic WO 3-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 WO 3-x films. We have found that while the small intercalating cations stabilize WO 3-x structure, the large nonintercalating surfactant cations (Et 4 N+, CtMe 3 N+) contribute to the dissociative reduction. While these cations do not affect WO 3-x structure of anodically protected films (E > 0.2 V), they cause surface lattice polarization on electron injection to the conduction band of WO 3-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.© Versita Warsaw and Springer-Verlag Berlin Heidelberg.

Simultaneous Electrocatalytic CO2 Reduction and Enhanced Electrochromic Effect at WO3 Nanostructured Electrodes in Acetonitrile

“…It is worth nothing that the use of voluminous cations, such as TBA + , does not allow intercalation due to steric hindrance and a different mechanism for the electrochromic effect, including electrodissolution has been considered. 25 In a CO 2 -purged solution, values of absorbance higher than for N 2 -purged solutions are consistently found, even at potentials where CO 2 reduction does not proceed (Figures 5b and S5).…”

“…In this respect, one should bear in mind that the tetrabutylammonium cation is more voluminous than the cavity available in WO 3 for intercalation, which is 0.52 nm in size. 25,44 This fact is important because with non-intercalating cations, a model for electrochromism with dissociative reduction of WO 3 has been considered. This mechanism entails a loss of mass (determined via electrochemical quartz crystal microbalance measurements), 45 due to the electrodissolution of WO 3 according to:…”

Spectroelectrochemical Study of CO2 Reduction on TiO2 Electrodes in Acetonitrile

“…It is worth noting that the electrosorption of the CO 2 molecule with concomitant partial oxide electrodissolution as is thought to be restricted to the interfacial region, without TiO 2 -3 significant structural damage in the subsurface region of the TiO 2 film. 32 Thus, the formation of the adsorbate induces several modifications in the interface, which are reflected TiO 2 -y (CO 2 ) in the development of capacitive currents promoting the generation of non-stoichiometric , together with the formation of species. This behavior would point to a TiO 2 -y TiOsynergistic effect between the CO 2 molecule and the surface: electrosorption triggers the activation of the CO 2 molecule together with the promotion of oxygen vacancies.…”

“…As in our previous work with WO 3 , to explain the unusual electrochromic effect accompanying CO 2 reduction, the model of electrochromism with large cation-containing electrolytes proposed by Hepel and co-workers is adopted. In this model, other processes such as lattice polarization, dissociative reduction, and electrodissolution are taken into account.…”

A Brief Overview of Electrochromic Materials and Related Devices: A Nanostructured Materials Perspective

“…The EC WO 3 layer is obtained as a thin film on a conductive substrate with an FTO or ITO electrode. There are several WO 3 fabrication techniques [99] (Figure 23), including magnetron sputtering [100], electrochemical deposition [101][102][103][104][105][106], spray pyrolysis [107], sol-gel [108,109], mechanical sputtering [110,111], etc. These technologies are based on electrochemical, chemical and physical principles.…”