设计构筑全共轭二维共价有机框架及其高能量密度柔性超级电容器

Covalent organic frameworks (COFs) have been regarded as promising electrode materials for flexible supercapacitors owing to their tunable porosity and reticular structural construction, which can not only stimulate the redox-active functionalities within the porous backbone, but also provide periodically ordered arrangement with high surface area accessible for efficient ion transport at the electrode/electrolyte interfaces. However, the low electrical conductivity and stacked architecture restrict their applications in supercapacitors, ascribing to the low electrochemical reaction kinetics, low utilization of active sites, and poor rate performance. Herein, a kind of fully conjugated COFs are proposed through C=C condensation reactions between tetra-aldehydes and di-acetonitriles. The conjugated effect of units will be extended to improve electrical conductivity of the COFs for improving the electrochemical reaction kinetics and rate performance. The electron-donating groups or electron-drawing groups will also be introduced into the structure, which would promote the electrochemical activity, and extend the operational voltage window for improving the energy density. Furthermore, 2D COF nanosheets with large specific surface areas will be prepared via a mechanical exfoliation treatment, then they can be used to constructed flexible supercapacitors via a 3D printing technology. The high porosity of electrode is beneficial for fast ions diffusion and transportation, thus resulting in a high power and energy density. The influences of conjugate and electronic effect, porous structure of units and the microstructure of electrodes on the electrochemical performance of flexible supercapacitor will also be studied systematically. The proposed project may provide a new method to realize flexible supercapacitors with high power density, high energy density, and long lifespan.

二维共价有机框架(2D COFs)因兼具有序多孔、大比表面积、结构稳定、富含电化学位点等优势，极具潜力构建高能量密度的柔性超级电容器。然而，2D COFs的层间柱状堆积及低导电性，使其电极反应动力学慢、倍率性能差、功率密度低。本项目拟通过共轭四醛与芳香二氰的Knoevenagel缩合反应，设计构筑以sp2 C=C偶联的全共轭2D COFs；调节单元共轭程度，增强框架π电子离域效应，促进电子传导和电化学反应，改善倍率性能；引入供、吸电子基团调控活性位点，拓宽电压窗口，提高电化学活性和能量密度；机械剥离实现2D COFs片层纳米化，增加其储能比表面积，继而辅以3D打印技术构筑三维多孔电极，加快离子扩散与传输，同时提高其功率/能量密度。研究构筑单元的共轭效应、电子效应、孔结构及电极微结构与器件性能之间的内在关系，揭示其储能机理，为构建高功率、高能量、长寿命的柔性储能器件提供新的方法和理论依据。

二维共价有机框架(2D COFs)因兼具有序多孔、大比表面积、结构稳定、富含电化学位点等优势，极具潜力构建高能量密度的柔性超级电容器，但其仍面临导电性低及堆叠结构引起的反应动力学慢、倍率性能差、功率密度低等问题。本项目基于2D COFs结构可设计性，拟以分子工程学为指导思想，选用具有良好π共轭效应的电化学活性结构单元，设计构筑全共轭、氧化还原活性2D COFs材料；通过调控构筑单元分子结构，引入分子间氢键，提高结构单元间的共面性，保证2D COFs晶体结构规整排列，扩展框架面内、面外π电子共轭体系离域，促进电子在框架结构内的传导，提高2D COFs材料本征导电性，优化倍率性能；改变活性位点类型，改善电化学活性，调控2D COFs电极材料电容行为的电位范围，拓宽可操作电压窗口，提高能量存储密度；通过电极材料结构设计，制备高比表面积的2D COFs基三维多孔电极材料，加快材料内离子扩散、传输，提高2D COFs活性位点的离子可及性及有效利用率，继而构建具有良好机械稳定性的高性能柔性超级电容器。该项目的实施将为设计新型2D COF材料以制备大功率、高能量密度、长寿命的柔性储能器件开启新的研究思路和实践基础。