Construction And Photoelectric Properties Study Of Nickel-based Electrochromic Nanomaterials And Multifunctional Devices

Electrochromic smart windows can reduce the energy consumption of building cooling,heating,and lighting by dynamically adjusting the incident light intensity of buildings,which has important application value in energy saving,emission reduction and efficient utilization of solar energy.The principle of smart windows is that electrochromic materials undergo charge transfer（i.e.redox reactions）under the action of an external electric field,resulting in changes in the optical absorption band,thereby selectively adjusting the absorption and transmission of natural light.Among them,nickel-based electrochromic materials have become a research hotspot because of their low cost and neutral coloring properties.However,the nickel oxide（Ni O）electrochromic materials currently studied have low intrinsic conductivity,limited electrochemical activity,and a single optical absorption band.As a result,the optical modulation range of such materials is low and the optical modulation band only occurs in the visible light band,and the practical application in the field of the electrochromic smart window is greatly limited.In response to the above problems,on the one hand,a phosphorus source was introduced into the nickel-based electrochromic material to enhance the electrochemical activity and reduce the charge transfer resistance.A bleached state with high transmittance and a colored state with low transmittance are achieved at low film thicknesses,thereby greatly improving the optical modulation range.On the other hand,the nickel-cobalt bimetal oxide was prepared by introducing cobalt elements into nickel-based electrochromic materials,resulting in the simultaneous regulation of visible light and near-infrared bands due to the synergistic effect of bimetal oxides.The details are as follows:Firstly,hydrated nickel hydride phosphate（Ni HPO₄·3H₂O）nanoparticle films were synthesized on fluorine-doped tin oxide（FTO）transparent conductive substrates based on the electrodeposition method.By adjusting the period of cyclic voltammetry in electrodeposition,Ni HPO₄·3H₂O film with optimal electrochromic properties was successfully prepared:ultra-high transmittance（≈100%）in the bleached state,large optical modulation（90.8%at 500 nm）,high coloring efficiency(75.4 cm² C^-1 at 500 nm),and excellent specific capacity(47.8 m Ah g^-1 at 0.4 A g^-1).The analysis shows that the introduction of a phosphorus source leads to the high electrochemical activity of the Ni HPO₄·3H₂O film,which can effectively accommodate hydroxide ions,resulting in improved ion injection/extraction efficiency in the material.In addition,this paper further constructed a large-size electrochromic smart window of 100 cm² using the Ni HPO₄·3H₂O film and electrostatically sprayed titanium dioxide（Ti O₂）film as the electrochromic layer and ion storage layer,respectively.The results show that the electrochromic smart window possesses the dual function of dynamic regulation of natural light and energy storage,which provides a research idea for the development of high-performance nickel-based electrochromic materials and devices.Secondly,in order to broaden the spectral modulation range of nickel-based materials to the near-infrared band,this paper induces the growth of nickel-cobalt bimetallic oxide（Ni Co O₂）nanowire array films on FTO by hydrothermal and thermal treatment methods.The electrochromic properties of the Ni Co O₂ film were optimal when hydrothermal reaction at 105°C for 90 min and thermal treatment at 350°C for 2 h by adjusting the parameters of the Ni Co O₂ preparation process.The Ni Co O₂ film achieves a wide-band optical modulation in both the visible light and near-infrared bands,and the optical modulation can reach 64.2%and41.8%at 550 and 1000 nm,respectively.In addition,the Ni Co O₂ film also delivers excellent optical memory ability（transmittance decayed by only 11.4%at 6.7 h）and energy storage performance(33.6 m Ah g^-1 at 0.25A g^-1).The results show that the introduction of cobalt elements realizes the simultaneous regulation of nickel-based materials in visible light and near-infrared bands.Finally,an electrochromic smart device was successfully assembled by using Ni Co O₂ and manganese oxide（Mn O₂）as the electrochromic layer and ion storage layer,respectively,which also showed excellent electrochromic and energy storage properties.