Controllable Synthesis, Film Preparation And Electrochromic Properties Of Nickel Oxide And Prussian Blue Nanostructures

Electrochromic (EC) devices have attracted significant attention because of their reversible color change and unique function of dynamically controlled solar energy gain. There are wide range of promising applications for EC devices in smart windows, rearview mirrors, displays, and so forth.In this paper, nanostructures of nickel oxide and Prussian blue were prepared by different methods respectively. Their electrochromic (EC) films were prepared by different methods, including deposition, spin-coating and electrodeposition. Their electrochromic properties were measured. The EC properties of materials are closely related to their morphologies and sizes. The main research contents are as follows:(1) Nickel oxide (NiO) micro/nanoflowers were synthesized by hydrothermal treatment followed by calcination. NiO films were prepared by deposition method. The structure, morphology and EC properties of NiO micro/nanoflowers and the as-prepared films were chanracterized and measured using X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetry (TG), UV-vis spectrophotometer (UV-2550) and CHI660D electrochemical workstatioa The concentration of potassium persulfate (K2S2O8) plays a significant role in the formation of the NiO micro/nanoflowers. A possible growth mechanism of NiO micro/nanoflowers is proposed. Conductive ions from the electrolyte are easily diffused into the thin nanosheets of the flower-like micro/nanostructures, resulting in the fast-response EC properties. The NiO film annealed at 300 ℃ for 1.5 h exhibits fast coloration/bleaching response (1.3 s for coloration and 3.2 s for bleaching) and high coloration efficiency (49.8 cm2·C-1) due to the flower-like micro/nano structures, showing a potential application in fast-response smart windows.(2) NiO ultrathin nanosheets with a thickness of～10 nm were synthesized by a template method. The concentration of urea plays a significant role in the formation of the NiO ultrathin nanosheets. NiO film was prepared by spin-coating polystyrene@Ni2CO3(OH)2 nanostructures on indium tin oxide (ITO) coated glass and calcination process. EC properties of NiO thin film were investigated in 1.0 mol·L-1 KOH by means of transmittance, cyclic voltammetry (CV) measurements. NiO film annealed at 300 ℃ exhibites noticeable electrochromism with photopic transmittance modulation of 40.1%, fast coloration and bleaching times of 5.4 and 3.6 s and high coloration efficiency (43.5 cm2·C-1).(3) Prussian blue (PB) films were prepared by electrodeposition. The morphology of PB film was controlled by using ITO conductive glass and ITO conductive glass spin-coated Ni3Si2O5 hollow spheres, respectively. The micro structure and morphology of products were characterized by XRD, SEM and TEM. The PB film used ITO conductive glass spin-coated Ni3Si2O5(OH)4 hollow spheres as substrate with roughly loose structure exhibites a noticeable EC performance. The variation of transmittance is up to 46.5% at 700 nm, the coloration/bleaching switching times are calculated to be 2.6 and 2.4 s, respectively. The PB film directly deposited on ITO conductive glass exhibits a transmittance change of 36.6% and coloration/bleaching switching times of 1.5 and 1.6 s, respectively.