Improved contrast between the coloured and transparent states in electrochromic Ni–Al layered double hydroxide films in mixtures of electroactive ions

Electrochromic Thin Films Based on NiAl Layered Double Hydroxide Nanoclusters for Smart Windows and Low-Power Displays

“…However, with Fe(CN) 6 4− , the transmittance of the reduced film returns to nearly 90%, leading to an enhancement of the electrochromic contrast. As already observed by Villemure and co-workers, 32 the bleaching of the film occurs in two steps, the first one corresponding to the direct reduction of Ni sites in the LDH and the second to the mediated reduction by Fe(CN) 6 , which remains an efficient mediator for the reduction in basic medium. The same tendency was clearly observed in DPA experiments ( Figure 5), highlighting the intrinsic advantage of using Fe(CN) 6 4− as a redox mediator.…”

“…40,41 The oxidation of NiAl-LDH NC is accompanied by a color change from clear to dark brown. 32 However, Villemure and co-workers 32 (and the cited references therein) have shown that the conductivity of fully reduced NiAl-LDH film is much lower than that of the partially oxidized film. Consequently, the formation of this reduced insulating phase at the interface between the LDH and FTO electrode slows down the reduction progress of nickel sites in the bulk of the film, leading to a shift of reduction potential (Ep c ) toward more cathodic values ( Figure S3).…”

“…In parallel, intrinsic EC properties of LDH matrices were also investigated by Villemure’s group. − As observed for NiO and Ni­(OH) 2 , in NiAl-LDH, the electrochemical oxidation of Ni sites in the layers is accompanied by a color change from clear to brown, which confers an EC behavior to this LDH. − However, the main limitations for the use of NiAl-LDH matrices in electrochromic devices are related to the low electrochemical accessibility of the Ni sites in the layer and the limited reversibility of the EC process, which induce a moderate contrast between the bleached and colored states and slow bleaching of the films. Interestingly, the addition of electroactive ions, such as [Co­(bpy) 3 ] 2+ , [Ru­(bpy) 3 ] 2+ , [Fe­(CN) 6 ] 4– , and [Ru­(CN) 6 ] 4– , in the electrolyte acting as electron mediators in the electrochemical oxidation and reduction of the Ni sites, is effective in improving the bleaching rate and the contrast of the film during the redox process . Further research is still required to obtain desirable homogeneous and transparent thin films of NiAl-LDH with improved accessibility of Ni sites and suitable EC properties.…”

A study of the effect of tungstate ions on the electrochromic properties of Ni(OH)2 films

“…This is related to changes in the equilibrium potential, which in turn, supposedly, changed because of structural changes of electrochromic material. Our assumption is that the exchange of ions that reside between the layers of the (001) plane occurs, similar to what's been described in the literature [28][29][30][31]33]. It should be noted that for Ni(OH) 2 [34] and nickel-based LDH [26,27,[35][36][37][38], the ions of source salts can reside between the layers in the direction of the (001) plane.…”

“…Considering these facts, it was decided to study the influence of 2 4 WO anion on electrochromic properties of nickel hydroxide. While the idea itself seemed interesting, no such data had been found in the reviewed literature [28][29][30][31].…”