Preparation Of Functionalized Two-dimensional COF Nanofilms And Their In-Plane Microsupercapacitive Properties

In-plane micro-supercapacitor（MSC）is an efficient miniaturized electrochemical energy storage device,with the advantages of high-power density,fast charge/discharge capability and excellent cycling stability.The main research goal in the in-plane MSC is achieving high supercapacitive performance in the tiny area,which can be achieved based on the design of high-efficient thin-film electrodes.Covalent organic framework（COF）material with designable regular porous structure,large specific surface area and high-exposed active sites,exhibit the great application potential in high-efficiency thin-film electrodes.In this paper,as for the hydroxylamine COF main research object,a series of COF_TAPB-DHPA thin-film electrodes were prepared by primitive structure design,morphology regulation and structural functionalization regulation,and further applied to assemble into in-plane MSC devices.The main research contents are as follows:（1）Hydroxylamine COF_TAPB-DHPA bulk and free-standing nanofilm were successfully synthesized by the solvothermal method and surfactant monolayer-assisted interface synthesis（SMAIS）method,respectively.The COF_TAPB-DHPA bulk with partially irregular stacking in the microscopic morphology,can exhibit the specific capacitance of 902.6 F·g^-1at 1 A·g^-1.While the COF_TAPB-DHPA free-standing nanofilm possesses the complete defect-free,large-area smooth crystalline structure（average thickness～11.0 nm）,and shows the specific capacitance of 4.58 m F·cm^-2 at 0.01 m A·cm^-2,the high volumetric capacitance of4163.64 F·cm^-3,and low charge transfer resistance of 0.01035Ω.These electrochemical performances are significantly better than those of COF_TAPB-DHPA bulk,which is attributed to the fact that the free-standing films with the regular one-dimensional pore structure,cannot only promote rapid electrolyte ion transport,but also exposes more active sites inside the pore.（2）According to pore space division and metal coordination post-modification strategies,the hydroxylamine COF skeleton was modified by in-situ grafting vinyl imidazole IL on the skeleton hydroxyl group and coordinating high redox activity Co²⁺on the skeleton imine nitrogen respectively,to prepare IL-COF_TAPB-DHPA and Co-COF_TAPB-DHPAfree-standing films and bulks.These two strategies promote the electrochemical double layer capacitance and Faradaic redox capacitance respectively,showing good capacitive performance:the areal specific capacitances of IL-COF_TAPB-DHPA and Co-COF_TAPB-DHPAfree-standing films were 4.81 m F·cm^-2 and 8.47 m F·cm^-2 at 0.01 m A·cm^-2,respectively,significantly higher than that of COF_TAPB-DHPA film(4.58 m F·cm^-2);the specific capacitance values of their bulks were 920.2 F·g^-1 and 1175.2 F·g^-1 at 1 A·g^-1,respectively,higher than that of COF_TAPB-DHPA bulk(902.6 F·g^-1).（3）The COF_TAPB-DHPA,IL-COF_TAPB-DHPA and Co-COF_TAPB-DHPA free-standing film interdigitated electrodes were prepared by mask-assisted technology,and assembled into corresponding MSC-COF_TAPB-DHPA,MSC-IL-COF_TAPB-DHPA and MSC-Co-COF_TAPB-DHPAdevices,respectively.The MSC-COF_TAPB-DHPA,MSC-IL-COF_TAPB-DHPA and MSC-Co-COF_TAPB-DHPA exhibit the maximum energy densities of 90.7 m Wh·cm^-3,139.7 m Wh·cm^-3and 230.4 m Wh·cm^-3,and the capacitance retention of 97%,80%and 80%after 5000 cycles of charge/discharge cycles,respectively.In addition,there is no obvious decrease in capacitance value for the MSC-Co-COF_TAPB-DHPA device,after the high-angle bending from0～180°and repeated bending.Moreover,the maximum energy density value ranked first among all reported 2D material in-plane MSC devices at this stage,which can effectively solve the stacking and aggregation problems of current thin-film electrodes based on the bulk,demonstrating the great supercapacitance performance traits compared with other conventional active materials.