Brown coloring electrochromic devices based on NiO–TiO2 layers

Abstract

Brown coloring electrochromic 5 Â 10 cm 2 windows with the configuration K glass/NiO TiO 2 / electrolyte/CeO 2 TiO 2 /K glass have been prepared and characterized by optoelectrochemical techniques (cyclic voltammetry, chronoamperometry and galvanostatic measurements). The electrochromic layers have been prepared by the sol gel technique. As electrolyte either a 1 M aqueous KOH solution or a newly developed starch based gel impregnated with KOH have been used. The CeO 2 TiO 2 sol gel layers sintered at 550 1C have been previously characterized in 1 M aqueous KOH electrolyte as a function of the thickness up to 2000 cycles and showed a highly reversible behavior without any corrosion effect. The NiO TiO 2 sol gel layers sintered at 300 1C have been extensively characterized in the same electrolyte up to about 7000 cycles. All windows present a deep brown color characteristic of the presence of Ni 3+ (NiOOH) species, that is fully reversible for several thousands of cycles with a rather fast kinetics (o30 s). The transmittance of the bleached state however slowly decreases with cycling (permanent coloration). The full bleached condition can be nevertheless recovered by applying a negative potential for a long duration. Deeper coloration is usually obtained by cycling the windows galvanostatically with a current density of 20 mA/cm 2. The lifetime of the windows is however limited because of the degradation of the NiO based layers due to the not fully reversible exchange of OH À that turns the layers mechanically fragile and leads eventually to their complete removal from the substrate. Windows working satisfactorily up to 7000 and 17 000 cycles have been obtained using aqueous KOH electrolyte and starch KOH gel electrolyte, respectively. Memory tests showed that the devices bleach at the open circuit potential from T 39% (colored state) to about T 50% in 60 min. .

A study of the effect of cycling modes on the electrochromic properties of Ni(OH)2 films

“…Nickel (II) hydroxide is anodic electrochromic material [5,6]. It switches from transparent to dark-brown upon anodic polarization according to the following reaction (1): Ni(OH) 2 [transparent]→NiOOH[dark-brown]+H + +ē.…”

Influence of Plasticizer Type on the Properties of Polymer Electrolytes Based on Chitosan

“…Advances in display technology, batteries, and electrochromical devices have stimulated the study of solid polymeric electrolytes (SPEs). These kind of materials with lithium salts dissolved in a polymer matrix have been widely studied ever since the pioneering works of Wright et al and Armand et al These polymeric materials represent a promising alternative for the substitution of liquid electrolytes and inorganic crystals used in batteries, sensors, and electrochromic devices. , Most of the systems described are composites and blends based on polyether chains that can be modified in order to decrease the crystallinity and glass transition temperature, improving the chain mobility and lithium ion conductivity. In addition, the world’s trends toward scientific and technological progress in the area of new materials indicate the importance of using industrial and agricultural residues as raw materials.…”

Microbial origin xanthan gum‐based solid polymer electrolytes

“…Among many different ionically conducting systems there have been also investigated the ones based on natural macromolecules such as gelatin, hydroxypropyl cellulose, starch, corn starch, chitosan, natural rubber, pectin, and agar . These SPEs have shown very promising features, and some of them were already applied in small electrochemical devices …”