| Electrochromism refers to the macroscopic reversible change in transparency of the light properties of material under external electrical signal.Electrochromic materials are generally divided into inorganic and organic electrochromic materials:Inorganic electrochromic materials get relatively long response time and strong device dependence,while the preparation and synthesis process of organic electrochromic is complex which are not resistant to ultraviolet radiation.MOFs can be used in the field of electrochromism with good redox and electrochemical activity.MOFs as a kind of crystalline materials that can be synthesis by hybridization of metal ions and organic ligands,possess the advantages of rich color change and fast color conversion of organic electrochromic materials,high coloring efficiency and stability of inorganic electrochromic materials.Triphenylene MOFs materials possess good electrochemical performance and redox activity due to the?-d conjugated hybrid orbitals which were widely used in sensing and energy storage among the MOFs materials.So triphenylene MOFs can also be one kind of electrochromic materials,and the performance of electrochromic electrodes composed of triphenylene MOFs is further studied in this paper.The gas-liquid interface method is used to grow the Ni3(HITP)2film,which can be quickly obtained in a short time.By adjusting the time during the crystal growth process of Ni3(HITP)2,Ni3(HITP)2 films with different thickness can be obtained.Through X-ray diffractometer(XRD),X-ray photoelectron spectrometer(XPS),Raman spectra(Raman),scanning electron microscope(SEM)and transmission electron microscope(TEM),the crystal structure,surface morphology,particle size and its distribution of the Ni3(HITP)2 film are characterized.Then,electrochemical workstation and UV-vis spectrophotometer(UV-vis)were used to test the electrochemical and electrochromic performance of the Ni3(HITP)2 electrochromic electrode.The results show that the Ni3(HITP)2 thin film electrode is composed of?15 nm two-dimensional nanosheets randomly stacked to form a porous structure.Due to its large internal voids,the electron transmission resistance is as low as?22?and the ion diffusion is relatively fast(?10-14)cm2 s-1),Ni3(HITP)2electrochromic electrode can quickly convert between blue-violet and yellow-green colors.The time of color conversion is 0.72 s/0.65 s?7.1 s/10.6 s,and the coloring efficiency is as high as 530 cm2C-1.In order to solve the problems of large randomness of the film thickness,the inability to prepare large-area films and the low utilization of organic ligands during the process of growing Ni3(HITP)2 films by the gas-liquid interface method,the layer-by-layer self-assembly method is adopted to control the number of cycles to accurately control the thickness of Cu3(HHTP)2 film with the potential to further assemble large-area electrochromic films.The Cu3(HHTP)2 film was synthesized in situ on the pre-treated and grafted FTO glass surface by layer-by-layer self-assembly method,and then XRD,XPS,Raman,SEM,TEM were used to analyze Cu3(HHTP)2 films with different cycles to characterize its phase,element composition and micro-nano structure.The electrochemical workstation and UV-vis are used to characterize the electrochemical and electrochromic performance of rigid electrochromic film electrodes of different periods.The results show that the Cu3(HHTP)2 rigid electrochromic electrodes film obtained by the layer-by-layer self-assembly method have a three-dimensional network structure composed of?20 nm nanoparticles and 2?6 nm gaps between the nanoparticles.The ion diffusion coefficient of Cu3(HHTP)2 rigid electrochromic electrode is about?10-13 cm2 s-1,with?51.3%light modulation range,1.8?3.2 s color transition time,632 cm2C-1 coloring efficiency,and its light modulation range can maintain61%after 100 cycles.In order to improve the problem that MOF crystal material cannot be used in the field of flexible electrochromism due to its brittleness,the FTO conductive glass substrate is replaced by ITO-PET film.After repeating the previous work,the Cu3(HHTP)2/ITO-PET flexible electrochromic electrode film with different cycles was obtained,and the electrochemical and electrochromic performance test was carried to study its performance.The results show that the Cu3(HHTP)2/ITO-PET flexible electrochromic electrodes possess three-dimensional network structure composed of?30 nm nanoparticles.The ion diffusion coefficient of Cu3(HHTP)2/ITO-PET flexible electrochromic electrode is about?10-13 cm2 s-1,and the light modulation range of the film is?30.3%regardless of bending 70°or under normal conditions.The time of color transition is as short as 0.6?4.5s,the coloring efficiency is 925 cm2C-1,and the light modulation range can still maintain 56% after 100 cycles. |
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