Construction And Multifunctional Engineerin Of High Ion-transport Porous Electrochromic Electrode

Electrochromic materials and devices have been studied for more than 50 years and have made significant progress in terms of assembly form,electrochromic effect,and types of materials.However,with the rapid development of flexible electronics,wearable devices and artificial intelligence,as well as the trend of device integration and miniaturization in recent years,both basic research and industry have put forward new demands for electrochromic devices,such as high flexibility,multi-color and multifunctionality.In the process of satisfying these urgent needs and realizing new functions,many new scientific fundamental questions have arisen,as follows:(1)Traditional transition metal oxide crystalline materials have a dense crystal structure with a compact atomic arrangement.The narrow lattice spacing slows down the ion embedding and removal process,higher energy is required to overcome the potential spatial resistance.;(2)Incorporating the functionality of flexibility to EC devices while maintaining high energy efficiency,fast switching speed and long durability have become increasingly critical;(3)Multifunctionalities and integration of devices are the development trend of basic research and industrialization.Most of the methods to achieve the multifunctionality of electrochromic devices are based on the direct superposition of different active materials or functional devices.In the process of miniaturization and multi-device integration of electronic circuits,the increase in the number of active layers brings problems of energy consumption,heat dissipation and interface,and multi-material compatibility and interface issues are also great challenges.In this paper,the correlation between the microscopic pore structure and the electrochromic properties of the electrodes is discussed in detail.In addition,the flexible semi-solid devices were prepared by using porous electrochromic films as electrodes,and their multifunctionality was systematically analyzed and studied from the perspective of electrochromic devices.The specific research is as follows:We successfully assemble Ti₃C₂T_x and the derived TiO₂ nanosheets into uniform nanometer-thick films at a liquid-liquid interface,and fabricate EC devices based on the TiO₂/Ti₃C₂T_x heterostructures on a flexible substrate.Due to the much-improved ion diffusion and electron conductivity of assembled single-flake-layer TiO₂ film and the 2D nature of both the MXene electrode and the TiO₂ EC layer,our devices are among the best flexible EC devices with the fastest coloration speed,the highest coloration efficiency and superior electrochemical stability.Na⁺intercalation electrochromism was demonstrated with the utilization of MOF films as a high-efficiency ion transport electrode,exhibiting rapid multicolor switching,high contrast,and high stability.The concept of ion-transport channel design for electrochromism was clarified by the intentional introduction of two kinds of NDI-based MOF films with various channel dimensions(radii of approximately 10 and 33(?)).These Na⁺intercalation EC films with desired ion-transport channel dimensions(radii of approximately 33(?))exhibited fast color diversity from transparent to red and then dark blue,accompanied by a high CE up to 260 cm² C^–1,good stability within 500cycles,and high optical contrast(?T?73%),which are the highest in the reported Na⁺-based EC materials and other MOF EC materials.A variety of conductive two-dimensional MOFs with large crystal domains was obtained by in situ transformation using a template transformation method using two-dimensional?-Ni(OH)₂ sheets as precursors,and the transformation process and efficient synthesis rules were studied in detail.Based on the obtained high quality two-dimensional MOFs,we prepared high performance electrodes with electrochromic properties,which showed much higher charge utilization than the conventional MOFs-based and other inorganic crystalline electrochromic materials,as well as excellent mechanical stability.Based on the finding on the color-sensing ability of the electrochromic(EC)materials,we develop a self-sensing electrochromic(SSEC)system that can mimic the functionality of the cephalopod-skin camouflage:the same device can perform color sensing and reversible fast recoloration in the visible and near-infrared regime simultaneously,giving rise to the autonomous color adaptability of the device according to its environment.This work demonstrates a single-body,inexpensive self-adaptive artificial camouflage with low power consumption and wide spectral range,which could be used in broad applications such as wearable electronics and advanced optoelectronics.