Targeted Construction Of Novel Covalent Organic Frameworks Towards Energy Storage And Conversion

Owing to the continuous growth in energy demand,the shortage of fossil fuels and the adverse impact of greenhouse gas emissions on the environment,the search for alternative renewable energy sources and the development of high-capacity energy storage technologies have been major needs facing modern society,the key to which is the development of sustainable,clean and low-carbon energy systems.With the gradual emergence of efficient energy storage methods such as rechargeable metal-ion batteries and photovoltaic devices in the clean energy sector,they are expected to complement fossil fuel energy sources,thus realizing a green energy transition.Compared with the inorganic materials typically used in metal-ion batteries and photovoltaic devices,organic materials are characterized by renewable resources,easy structural modification,and environmental friendliness.However,the low porosity and poor electrical conductivity of organic materials limit the exposure of active sites and carrier transport,which seriously affects their further broad applications.Covalent organic frameworks（COFs）with excellent physical and chemical stability are a class of crystalline organic porous materials based on stable covalent bonding between organic molecular blocks.COFs materials have the advantages of pre-designed topologies,adjustable pore sizes,and diversified building blocks,which endow them with highly efficient pathways for material transport and specific photo-/electro-active groups.Through the fine tuning of COFs synthesis methods and the rational design of COFs building blocks,topologies,bonding modes and functional sites at the molecular level,the targeted construction of COFs materials with efficient energy storage and conversion can be realized.In this thesis,three novel COFs materials were constructed by imine/imide condensation reaction with photo/electroactive N,N,N’,N’-tetrakis（4-aminophenyl）-1,4-phenylenediamine（TPDA）as the core building block.Their applications in lithium-ion batteries（LIBs）and perovskite solar cells（PSCs）were investigated in detail.The details of the study are as follows:1.COF_{TPDA-m DA} with one-dimensional（1D）chain structure was designed and synthesized by using TPDA with electroactive moiety as the C₄ building block and isophthalaldehyde（m DA）with V structure as the C₂ linking block.The structure facilitates the exposure of active sites and promotes the interactions between ions in the electrolyte and the active centers on the skeleton of the COFs.The C-N provides active sites and high redox potential for COF_{TPDA-m DA}.And the C=N formed between TPDA and m DA provides another active site.The synergistic effect of C-N and C=N provides high energy density for LIBs cathode materials.COF_{TPDA-m DA} was combined with reduced Graphene Oxide（r-GO）to improve its conductivity.The composite COF_{TPDA-m DA}@50%r-GO exhibited excellent electrochemical performance.Even after 100cycles at a higher current density of 0.2 A/g,COF_{TPDA-m DA}@50%r-GO can still maintain a high specific capacity of about 120 m A h/g.Thanks to the joint contribution of pseudocapacitance and diffusion process,COF_{TPDA-m DA}@50%r-GO has good multiplicative performance.The strategy of simultaneous modulation of COFs backbone structure and active sites provides a feasible approach for the rational design and synthesis of LIBs cathode materials.2.The poor reversibility of the imidation reaction and the fast reaction rate between monomers lead to difficulties in the synthesis of highly crystalline PI-COFs with high specific surface area.Based on this,a water-assisted synthesis method was developed to successfully synthesize highly crystalline COF_TPDA-PMDA with a kgm topology using TPDA and phthalic tetracarboxylic anhydride（PMDA）as C₄ and C₂ linker blocks,respectively,with a high specific surface area of up to 2669 m²/g,which facilitates the interaction of ions in the electrolyte with the active sites of COF_TPDA-PMDA and improves its mass transfer effect effectively.The synergistic effect of C-N and C=O active sites gives COF_TPDA-PMDA a high energy density,while the high crystallinity improves the stability of PI-COFs during long-term charging and discharging.COF_TPDA-PMDA@50%CNT prepared by combining COF_TPDA-PMDA with carbon nanotubes（CNTs）can be used as a cathode material for LIBs.COF_TPDA-PMDA@50%CNT has a high initial charging capacity of 233 m Ah/g（0.5 A/g）.Even at a high current density of 5 A/g,COF_TPDA-PMDA@50%CNT maintained a specific capacity of 80 m Ah/g after 1800cycles.The optimization of the water-assisted synthesis method provides an idea for the design and synthesis of highly crystalline PI-COFs-based energy conversion and storage materials with high specific surface area and multiple active centers.3.Heteroatoms containing lone-pair electrons can coordinate with Pb²⁺in the perovskite precursor,affecting the crystallization process of chalcogenide,inhibiting the decomposition of chalcogenide,and improving the power conversion efficiency of PSCs.The D-A structure,on the other hand,can provide an additional charge transfer pathway that effectively prevents photogenerated carrier complexation,thus providing higher charge separation efficiency.Based on this,heteroatom-rich thiazolo[5,4-d]thiazole（TZ）-based D-A-type COF_TPDA-TZDA were designed and synthesized using TPDA and 4,4’-（thiazolo[5,4-d]thiazole-2,5-diyl）dibenzaldehyde（TZDA）as the C₄ and C₂ connecting blocks,respectively.The TPDA serves as the electron-donor unit,whereas TZDA not only serves as the electron acceptor unit,but its TZ fragment also provides abundant coordination sites.X-ray photoelectron spectroscopy（XPS）results demonstrated that the Pb²⁺in the perovskite film containing COF_TPDA-TZDA showed lower binding energy compared to the control perovskite film due to the fact that the N atom with electron-donating property in the TZ functional group N atoms with electron-donating properties in the TZ functional group can interact with Pb²⁺through coordination effects.The incorporation of COF_TPDA-TZDA with D-A structure not only improves the crystallinity and grain size of perovskite film,but also provides additional charge transfer pathways to inhibit the perovskite defects and promotes the migration of charges within the perovskite film.The PSCs modified with COF_TPDA-TZDA showed a power conversion efficiency（PCE）was as high as 23.51%,and remained above 90.55%of the original PCE after 480 h of storage at 60%humidity.The targeted regulation of the building blocks and active sites of the COFs provides a reference for the development of efficient and stable PSCs devices using TZ-based D-A-type COFs.