Reaction (2) is being responsible for the electrochromic behavior of
WO3 films. Reichman et al. [34] reported digital simulations of this
process on both evaporated and anodic WO3 films. The authors
managed to reproduce experimental behavior assuming rate determining
processes to be: (i) charge transfer to H+ on WO3/solution
interface, (ii) diffusion of H atoms within the film and (iii) buildup
of H atom concentration within the film. On anodic WO3 films
rather reversible behavior was observed, compared to evaporated
films, while the value of the diffusion coefficient of H atoms in
the film was found to be 5 108 cm2 s1. Hence, diffusion limitations
imposed to voltammograms presented in Fig. 1 cannot be assigned
to the process of bronze formation but rather to hydrogen
evolution, confirming the applicability of Eq. (1) for the analysis
of the recorded currents. In addition, successive potential cycling
in the region more negative relative to that at which surface oxidation
may take place, removes the oxide layer, as evidenced by
means of oxygen reduction reaction onWelectrode in alkaline solutions
[37].