Electrochromic Behavior Of NiO-TiO₂ Films Prepared With Surfactant Added To The Sol

Electrochromism is a phenomenon in which a reversible change in optical properties occurs under an applied voltage. Nickel oxide is an anodic electrochromic material which is able to change colour from transparent to a deep brown colour at positive potentials and then is reversibly bleached when a Onegative potential is applied.In this paper, films of NiO-TiO2 with Ni concentration of 80 mol% have been obtained using ethanolic and n-butanolic sols with nickel acetate tetrahydrate (Ni(CH3COO)2.4H2O) and tetra-n-butyl titanate (TNBT) as precursors via the sol-gel route by dip coating technique and sintered at 300℃. The effect of surfactant including sodium dodecyl sulphate (SDS), cetyltrimethylammonium chloride (CTAC), poly ethylene glycol (PEG) and dodecyl dimethyl betaine (BS-12) to the nickel oxide sol and films were tested. The effect of sodium dodecyl sulphate (SDS) to the sol and layers was researched in detail.The thermal analysis of dried xerogels has been measured by thermogravimetry (TG) and differential thermal analysis (DTA) in air up to 500℃. The structural properties of xerogels sintered at 300℃ have been determined by XRD and consist predominantly of bunsenite nanoparticles embedded in an amorphous TiO2 phase. Single layers have been deposited by dip coating on FTO coated glasses and sintered at 300℃. Their thickness is found to increase with the SDS amount while the roughness of the surface is reduced. The electrochromic properties of films deposited on FTO coated glasses have been studied in 1 M KOH aqueous electrolyte via cyclic voltammetry (CV), chronoamperometry (CA) and visible light transmission. The anodic and cathodic peaks in CV cycles and the charge intercalated during CA cycles increase with the SDS content. The transmission in the bleached and colored states as well as the optical density remain stable for the film prepared with 9 wt% SDS up to almost 18000 CA cycles, a great improvement compared to films prepared without surfactant. The coloration efficiency of the film prepared with 9 wt% SDS is about 30 cm2/C, a value comparable to that obtained for pure NiO film. The best composition to get stable sols and higher reversible transmittance change layers were obtained with single layer-coating of NiO-TiO2 sol doped 9% SDS, aging six days.