Preparation Of Three-dimensional Ordered Macroporous Nickel Oxide Thin Films And Their Electrochromic And Energy Storage Properties

Electrochromism refers to the phenomenon that the optical properties of the electrode material are able to be changed reversibly by intercalation/de-intercalation of electrons and ions under a certain electric field.A capacitor is a device that can store and release electricity and electrical energy.As a transition metal oxide electrode material,nickel oxide(Ni O)has large optical modulation,high specific capacitance and good durability.It is an ideal bi-functional material that can realize both electrochromism and energy storage.In this paper,Ni O films with three-dimensional ordered macroporous structure(3DOM)were prepared on transparent conductive indium tin oxide(ITO)glass substrates,exhibiting good electrochromic and energy storage performance.In order to study the effect of electrode material structure on optical properties,polystyrene(PS)templates with different particle sizes were prepared by the vertical deposition method,and then nickel hydroxide(Ni(OH)₂)was filled into the gaps by applying a constant potential.Then the templates were removed by immersing in toluene to obtain 3DOM Ni(OH)₂ films with different pore sizes and thicknesses.Finally,3DOM Ni O films with different pore sizes and thicknesses were obtained by annealing.Results showed that all of the PS templates,3DOM Ni(OH)₂ and 3DOM Ni O films had the characteristics of three-dimensional ordered structure and photonic band gap,and the appearance of the structure color varies with the angle.The photonic band gap reflectance was related to the thickness of the film,and the position was related to the periodic structure size and refractive index of the material.The electrochromic performance of the 3DOM Ni O thin films was studied.The 3DOM structure allowed for thin wall thickness and large specific surface area,leading to the short ion diffusion distance,and more ions and electrons were involved in the electrochemical reaction.The optical modulation of 3DOM Ni O thin films was 24.8%,and the coloration efficiency was 58 cm²·c^-1.Moreover,their colors can be switched quickly with the coloration time of 2.2 s and the bleaching time of 0.5 s,the diffusion coefficient of lithium ion was3.78×10^-9 cm²·s^-1.Compared with the dense Ni O film,3DOM Ni O films showed stronger binding force to the ITO substrates.After 500 voltammetry cycles,they still retained good electrochromic performanceand memory effect.The energy storage performance of 3DOM Ni O thin films was also studied.It was found that 3DOM Ni O thin films tended to be pseudocapacitive.The high symmetry of voltammetry curves and obvious redox peaks indicated that 3DOM Ni O thin films could transport and store electrons and ions through a reversible redox reaction.The specific capacitance of the films could reach 3.9 m F·cm^-2when the current density was 1.0 m A·cm^-2,and after 500 times of constant current charge and discharge,the specific capacitance could still maintain 91%of the initial value,indicating the good cycling stability of the 3DOM Ni O thin films.