Electrochromic materials are energy-saving and environmentally friendly materials that can reduce energy use by adjusting sunlight and solar-heat. In particular, transition metal oxides with stable chemical properties have been widely studied as electrochromic materials. Recently, bimetallic oxides with two variable valence states of metal ions have received increasing attention due to their better electrochemical activity. In this study, Ti₂Nb₁₀O₂₉ films were successfully prepared on conductive glasses, and the effect of the atomic ratio of niobium to titanium in the precursor on the electrochromic properties of the thin films was investigated. The results show that the thin film prepared from precursors with an atomic ratio of niobium to titanium of 3 : 1 possesses the best electrochromic properties. It is worth noting that the thin film achieves a large optical modulation in the wavelength range of 300-1100 nm, and the transmittance in the bleached state is nearly 90%, appearing grayish blue under the action of −1.6 V, colorless state under the action of 0.4 V, and achieving a maximum optical modulation of 69.4% at the wavelength of 750 nm. After a square-wave potential of -1.6 V for 60 s and 0.4 V for 15 s, the film shows response time of 29.8 s for coloring and 5.9 s for bleaching. Coloration efficiency of the as-prepared film is 68.3 cm²·C^-1. The above results indicate that the successfully prepared Ti₂Nb₁₀O₂₉ thin film enriches variety of bimetallic oxide electrochromic materials and has widely application prospect.

Electrochromic materials have been applied in energy-saving buildings, intelligent displays, and other fields, recognized as one of the most promising intelligent materials for research. Liquid phase method for preparation of WO₃ electrochromic thin filmscan construct complex polychromies structures, showing great potential in modulation amplitude and short response time, especially in large area and low cost preparation. This study aims to develop a low-cost, easy-to-scale WO₃ nanocrystalline liquid phase coating process, and improve cycle stability and preparation process. WO₃ electrochromic films with high modulation amplitude, rapid response and fatigue resistance were prepared. Optimized the annealing process, WO₃ nanopowders were synthesized with low aggregation and high crystallinity, and then WO₃ nanocrystalline coating solution was prepared by ball milling dispersion. Thin film microstructure and coating solution crystallinity were optimized. The obtained thin electrochromic films of WO₃ show high tuning amplitude (82%), short response time (t_c/t_b: 8 s/4.2 s), high colouring efficiency (81.5 cm²·C^-1), and high cycling stability (> 1000 times). In this work, the crystallization and dispersion properties of WO₃ nano-powder were modified to comprehensively improve the performance of WO₃ electrochromic films prepared by nanocrystalline liquid phase coating technology. All results above demonstrate that the WO₃ electrochromic film prepared by the liquid phase method is expected to be used in the future with high color-changing performance and cycle stability.

Nickel molybdate (NiMoO₄) is a material with excellent performance in the field of energy storage and catalysis, but lacking of further explorations in the field of electrochromism. In this work, porous NiMoO₄ films were grown on transparent conductive glasses by hydrothermal method without using seed layer. Crystalline phase and micromorphology of NiMoO₄ nanosheet films were characterized by grazing incidence X-ray diffractometer (GIXRD) and field-emission scanning electron microscope (FESEM), and the electrochromic and electrochemical properties were also investigated by using a UV-Vis-NIR spectrophotometer and an electrochemical workstation. The results show that the NiMoO₄ electrochromic films have a porous structure, which can provide sufficient channels for ion migration and reactive sites for the dynamic process of ion intercalation/deintercalation into NiMoO₄ film. Therefore, the NiMoO₄ films exhibit excellent electrochromic performance, including large optical modulation of 79.6% at 480 nm and high coloring efficiency of 86.2 cm²·C^-1. Meanwhile, the coloration and bleaching response time of the NiMoO₄ films are 9.5 and 12.7 s, respectively. Interestingly, there is a two-step process in the bleached process of NiMoO₄ electrochromic films, including a fast process and a slow process. And the optical modulation can still be maintained at 99.7% of the maximum optical modulation after 100 cycles. In addition, the NiMoO₄ films exhibit a large area specific capacitance of 49.59 mF·cm^-2 at 0.3 mA·cm^-2. These excellent properties support NiMoO₄ nanosheet films with promising application in high-performance electrochromic devices. And the next step is to focus on finding the suitable electrolyte and matched counter electrodes in the device assembly.

Electrochromic materials can be used in new display devices because of their color-changing properties with applied voltage. The current multicolor electrochromic devices (MCECDs) are mostly prepared using several organic materials of different colors, and their process is relatively complicated, leaving preparation of simple MCECDs is still a challenge. In order to simplify the preparation process, we proposed a Prussian blue analogue composite electrochromic (MC PBA) film with four typical color states of red, blue, green, and yellow for excellent performance ECD. In this work, the preparation of a Zn-Fe Prussian blue analogue composite (Zn-Fe PBA) film was proposed by a two-step electrodeposition method. It has only one pair of redox peaks in the cyclic voltammetry curve, which corresponds to the redox reaction between Fe^Ⅲ/Fe^Ⅱ. The electrochemical performance of the Zn-Fe PBA film is excellent, which hardly degrades after 10000 cycles. It is white with almost no color change during electrochemical redox, and does not affect the color when assembling multicolor electrochromic device (Z-MCECD) with MC-PBA film. In addition, the Zn-Fe PBA film is used as ion storage layer which can significantly reduce the overpotential from 4.0 V to 1.5 V in the corresponding ECD. Benefiting from the advantages of Zn-Fe PBA film, Z-MCECD maintains four typical color states of red, blue, green, and yellow, while the operating voltage is lower and the cycle stability is also significantly improved. The transmittance control range within 2400 s was almost no attenuated, and after 3600 s, transmittance still maintained 74.4% of the initial, while the multicolor group experienced completely irreversible performance loss after 1200 s. Z-MCECD has great application potential in color electrochromic display field.

Graphene has played a major role in wearable electronic textiles due to its excellent electrical conductivity, superior flexibility and environmental stability. In this work, a green-yellow reversible electrothermochromic fabric was constructed via a facial double side coating. The self-made graphene paste is coated on the surface of polyester fabric by screen printing technology. The hybrid thermochromic ink with reversible color-changing property is coated on the opposite side of the graphene layer by screen printing technology. Structural properties and discoloration principle of the fabric were analyzed. Their thermal and color-changing properties were studied by using infrared thermal imaging and colorimeter. The results show that the graphene forms a conductive layer with a thickness of 250 μm that allows Joule heating to supply the thermal resource for the electrothermochromic behavior. This fabric changes from green to yellow with a gradual heating that exceeded 45 ℃ at 12 V due to the ring closure and opening of crystal violet lactone. Its color change response time is about 15 s, while fading response time is about 27 s. The electro-thermochromic fabric is not disturbed once undergoing a bending angle range from 30° to 180° and the voltage-current curve remains stable. Performance of the fabric does not significantly degrade after 200 heating/cooling continuous cycles. In conclusion, a sensitive electro-thermochromic fabric with good cycle performance from green to yellow with the structure of graphene film‖polyester fabric‖thermochromic film is successfully prepared, which has a high application potential in the fields of military camouflage and wearable display.

Room temperature ionic liquid shows wide electrochemical windows and good environmental stability, which is expected as an ideal electrolyte for electrochromic devices. However, the small crystal spacing of traditional electrochromic materials limits the diffusion of large ions in ionic liquid. Repeated deintercalation/ intercalation of large ions could also destroy the structure of traditional electrochromic materials, resulting in performance degradation. Metal-organic frameworks (MOFs) are topologically porous materials with a large intrinsic nano to microporous structure in crystalline, which are expected to provide channels for transporting large-sized ions in ionic liquids. In present work, triphenylene-based MOFs Cu₃(HHTP)₂ films were prepared on the surface of the conductive glass. Electrochemical and electrochromic behavior of Cu₃(HHTP)₂ films were studied in traditional propylene carbonate (PC)-based electrolyte and ionic liquid-based electrolytes. The results show that, compared with the traditional LiClO₄/PC or NaClO₄/PC electrolyte, Cu₃(HHTP)₂ film displays low contact resistance and high ion diffusion efficiency in the ionic liquid [EMIm]BF₄ electrolyte. Switch speed of the electrochromic electrode is significantly improved with coloring time being reduced from 10.3 s to 8.0 s, and bleaching time being reduced from 23.6 s to 5.2 s. Meanwhile, Cu₃(HHTP)₂/[EMIm]BF₄ electrochromic system also shows a larger light modulation range and coloring efficiency. This work demonstrates the potential of MOFs/ionic liquid electrochemical system in the field of electrochromic device.

Perovskite manganese oxide (PMO) has attracted extensive attention in the field of heat dissipation because of its discoloration stimulated by external conditions. At present, most of the researchs on the discoloration characteristics of PMO is based on temperature excitation, and there still lacks of heat dissipation equipment excited by electric field. In addition, because the electric field excitation is accompanied by Joule heat, electrochromic property of PMO materials has not been clearly proved. In view of the above challenges, here an electrical modification method for PMO materials is proposed by using influence of electric field excitation on Mn elements in PMO. Thermochromic property of PMO was greatly weakened by electrical modification, and then La_0.7Ca_0.25K_0.05MnO₃ (LCKMO) can eliminate the influence of Joule heat in electric field excitation experiment. We studied the thermochromic and electrochromic properties of LCKMO before and after electrical modification. Emittance of LCKMO before electrical modification increases with the increase of temperature with the maximum increment at 17%. After being excited by 21 V electric field, the emittance increases by 15%, 16%, 10%, 0.6% and 1.4% at 173, 203, 243, 273, and 373 K, respectively. The thermochromic property of electrically modified LCKMO is greatly weakened, and its emittance increases by 10.7% and 9.3% at 273 and 373 K, respectively, after being excited by 21 V electric field. The experimental results before and after electrical modification show that LCKMO has electrochromic property, and there is an obvious regulation mechanism of electric field excitation on the emissivity. Therefore the electrical modification method for PMO materials can not only enable the electrochromic study of PMO materials without the influence of Joule heat, but also provides a new possibility for regulation of the thermochromic property of PMO materials.