Proton Insertion in Polycrystalline WO3 Studied with Electron Spectroscopy and Semi-empirical Calculations

Henningsson, A. Stashans, A. Sandell, H. Rensmo, S. Sodergren, H. Lindstrom, L. Vayssieres, A. Hagfeldt, S. Lunell and H. Siegbahn  

Dedicated to Professor Osvaldo Goscinski on the occasion of his 65th birthday. 

ADVANCES IN QUANTUM CHEMISTRY, VOLUME 47 ISSN 0065-3276 DOI 10.1016/S0065 3276(04)47002-6 

When ions are inserted into WO3, both X-ray photoelectron spectra and electron spin resonance show that as well as W are present, and that the density scales with the intensity of the electrochromic absorption peak [2,9]. The picture that emerges is that the inserted electrons are localized at tungsten sites, where they participate in processes responsible for the electrochromism. The insertion/extraction process can then be represented, schematically, by 

Interestingly, cyclic voltammograms (CVs) of monoclinic films prepared by chemical vapour deposition (CVD) [10] showed clear peaks both in the cathodic and anodic sweep directions, indicating different electrochemical processes in specific voltage ranges. It was discussed [10] that these features could be due to from two sources adsorbed on the oxide surface and in the bulk of the electrolyte. Alternatively, at least two redox waves in the CV can be interpreted hy a two-step oxidation of WO3, from W to W and then further to a state. The existence of W states during proton insertion in evaporated amorphous WO3 films for x 0.3 has been discussed by Ottermann et al. [11]. 

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Proton Insertion in Polycrystalline WO3 Studied with Electron Spectroscopy and Semi-empirical Calculations... 

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