The Preparation And Properties Of NiO-based Nanocomposite Electrochromic Films

The electrochromic materials have the functions of energy conservation,environmental protection information display and so on.It has a very wide application prospect in the fields of military camouflage equipment,displays and sensors.In recent years,many achievements have been made in the study of NiO electrochromic films.But due to the problems of cycle stability,coloration efficiency of NiO films,the application of pure NiO electrochromic films was limited.In order to improve the cycle stability,coloration efficiency and other properties of NiO films,Ni/NiO/rGO and Ni/NiO/C nanocomposite electrochromic films were prepared by sol-gel method.The addition of GO and carbon black introduced metallic Ni particles into the composite film,and improved the electrochromic performance of NiO films.On the basis of these results,the growth mechanism of nanocomposite films was explored,and the optimum technological parameters were determined.The main results are as follows:（1）Through the exploration of preparation conditions,the two-step heat treatment method of vacuum followed by air was adopted.The heat treatment temperature was 350℃ and holding time was.10 mins.The main form of Ni in Ni/NiO/rGO nanocomposite electrochromic films were NiO and Ni phases.The thickness of the composite films were controled at about 83±2 nm.The surface of the composite electrochromic films with different GO contents were uniform and dense,and no obvious cracks or holes were found on it.When the GO content was 3%,Ni/NiO/rGO composite film exhibited a large optical modulation range △T550nm=51.6%.The coloration efficiency reached a maximum of 48 cm²·C^-1,and the response times of coloring and erasing were 4.2s and 2.4s,respectively.（2）On the basis of these experimental results,the growth mechanism of Ni/NiO/rGO nanocomposite films was presented.The GO layer can bond well with Ni（OH）2 during sol-gel process,and C-O-Ni bonds were formed during heat treatment.Metallic Ni particles are mainly derived from the reduction of NiO matrix by the carbon atoms falling off GO ring.And when the concentration of graphene oxide is higher than 3%,the number of functional groups available is inversely proportional to the concentration of graphene oxide.Just like the dispersion of graphene oxide reached the saturation point.Therefore,with the increase of the graphene oxide concentration,the response time,diffusion rate and the content of nickel ions increased firstly and then decreased.（3）In order to explore the effect of GO,Ni/NiO/C nanocomposite electrochromic films were prepared by the same method with carbon black as additive.The results show that the addition of carbon black could obtain the metal nickel particles either,and the main form of Ni element were NiO and metal Ni.However,due to the poor dispersibility in the composite sol,it is hard for carbon black to buffer the internal stress generated during the heat treatment like GO did,leading many cracks and holes appeared on the surface of Ni/NiO/C nanocomposite electrochromic films,and it is difficult to adjust the films thickness uniformly.The cyclic stability of the composite film is poor,after 400 cycles,there was obvious shedding occurred.And the response speed did not increase significantly.For Ni/NiO/C composite films,it accords with the function mechanism of dispersion ability of Ni/NiO/rGO nanocomposite films,the dispersibility of carbon black could also affect the properties of the films.When the carbon black concentration is 0.3%,Ni/NiO/C composite films exhibit a large optical modulation range △T550nm=60%,CE reached a maximum of 42.79 cm²·C^-1。...