2D Molecular Sheets of Hydrogen‐Bonded Organic Frameworks for Ultrastable Sodium‐Ion Storage

Abstract

little volume change during cycling. [15,16] It should be noted that albeit with high theoretic capacities, small organic molecules are often subjected to dissolution in the electrolyte at their charged or discharged states, and thereby suffer from very poor cyclability. [16] Poly merization through covalent bonding represents an effective strategy to suppress their dissolution. [17][18][19] A number of conjugated polymers (such as covalent organic frameworks or COFs) with different building units and topologies have been accordingly explored. [20][21][22][23][24][25] They often have low structural crystallinity and unsatisfactory cycling stability limited to a few hundreds of cycles.In addition to covalent bonding, some organic building blocks (such as those containing carboxylic acid or amine functionalities) may also self-assemble through weak hydrogen bonding to form ordered two-dimensional (2D) or three-dimensional (3D) frameworks known as hydrogen bonded organic frameworks (HOFs). [26][27][28][29] They generally have great structural crystallinity, large surface areas and porosity, and have been widely investigated for gas separation, sensing, proton conduction and so on. [26,27,30] Unfortunately, their potentials in electrochemical energy storage are elusive since the weak hydrogen bonds would be disrupted in common organic electrolytes, eventually leading to the collapse of ordered frameworks. [27,30] The construction of chemically stable HOFs remains a challenging task, and necessitates the design of novel linker units capable of forming multi-site hydrogen bonds.To this end, we here introduce diaminotriazole (DAT) as the linker unit for the first time in the construction of chemically stable HOFs. DAT is a nitrogen-rich heterocycle that can potentially forms multiple hydrogen bonds. Its reaction with dianhydride gives rise to imide building blocks that further selfassemble in solution to form 2D HOF molecular sheets. Owing to the multi-site hydrogen bond interactions (eight H-bonds per building blocks), the resultant product is highly robust in spite of its ultrathin thickness of ∼1 nm, and has diminished solubility in most polar or non-polar organic solvents. When evaluated as the cathode material of SIBs, HOF molecular sheets deliver a large capacity, and most surprisingly, outstanding cycling performance of >10,000 cycles at 1 A g −1 that is far from attainable with conventional organic electrode materials in our best knowledge. This impressive electrochemical performance is afforded by the high chemical stability and fast Na + diffusion There has been growing research interest in hydrogen bonded organic frameworks (HOFs) by virtue of their great structural crystallinity, large surface areas and porosity. Their potential in electrochemical applications, unfortunately, remains elusive because weak hydrogen bonds would dissociate in solution that eventually compromises the structural integrity. Herein, it is demonstrated that this issue may be overcome by designing and introducing multisite hydrogen bo...

A metal-organic framework@hydrogen-bond framework as a matrix for MALDI-TOF-MS analysis of small molecules

“…The characteristic peaks located at 1597 cm −1 and 1392 cm −1 can be attributed to the asymmetric and symmetric stretches of the –COO– groups in the terephthalate ligand, 15 respectively. The peak of 2926 cm −1 can be ascribed to the O–H stretching vibration of N–H⋯O, and the peaks of 3068 cm −1 and 3248 cm −1 can be attributed to the N–H stretching vibration of N–H⋯N, 13 respectively, which indicates the existence of hydrogen bonding in the HOF material. In addition, the absorption peaks at 3200–3500 cm −1 can be attributed to the stretching vibration of the –OH group.…”

“…12 The diffraction peaks marked at 2 θ = 12.4°, 21.5°, 25.1°, and 29.2° are assigned to the HOF structure. 13 The wide-range X-ray photoelectron spectroscopy (XPS) survey spectrum (Fig. 2b) shows the presence of C, N, O, and Zr elements.…”

Synthetic Control of Electronic Property and Porosity in Anthraquinone-Based Conjugated Polymer Cathodes for High-Rate and Long-Cycle-Life Na–Organic Batteries

“…Redox organic compounds are promising candidates as cathode materials for rechargeable batteries, by virtue of the advantages of renewable resources, low cost, and green synthesis with a low carbon footprint. − Since the report of an organic cathode of dichloroisocyanuric acid in 1969, abundant redox compounds have been explored as organic electrode materials in various kinds of batteries. Among the reported organic electrodes, carbonyl compounds are some of the most competitive n-type cathode materials for SIBs, such as quinones, , imides, , and cyanuric acids, , due to the features of high theoretical capacities, high redox potentials, diverse structures, and extensive sources. , However, the high solubility of carbonyl compounds in organic electrolytes could result in a fast capacity decay during the cycling process, which is a showstopper hindering their practical applications. − Increasing molecular weights by polymerization and introducing polar groups (e.g., COONa, SO 3 Na, aminotriazole) are two of the most adopted and universal strategies to tackle the dissolution issues of organic cathodes for SIBs. − For instance, Tang et al reported a poly­(pentacenetetrone sulfide) (PPTS) cathode that could deliver a stable cycling performance of more than 10000 cycles with a capacity retention of 88%, while PPTS suffered a relatively poor rate capability possibly due to its nonconjugated and densely stacked polymer chains that might block the charges transfer . Wu et al introduced two aminotriazole polar groups into 1,4,5,8-naphthalenetetracarboxylic diimide (NTCDI) to synthesize a hydrogen-bonded organic framework (HOF-DAT), which achieved more than 10000 cycles with a capacity retention of 65%, since the formation of multiple hydrogen bonds between intramolecular aminotriazole groups reduced the solubility of HOF-DAT in most organic solvents .…”

“…Among the reported organic electrodes, carbonyl compounds are some of the most competitive n-type cathode materials for SIBs, such as quinones, , imides, , and cyanuric acids, , due to the features of high theoretical capacities, high redox potentials, diverse structures, and extensive sources. , However, the high solubility of carbonyl compounds in organic electrolytes could result in a fast capacity decay during the cycling process, which is a showstopper hindering their practical applications. − Increasing molecular weights by polymerization and introducing polar groups (e.g., COONa, SO 3 Na, aminotriazole) are two of the most adopted and universal strategies to tackle the dissolution issues of organic cathodes for SIBs. − For instance, Tang et al reported a poly­(pentacenetetrone sulfide) (PPTS) cathode that could deliver a stable cycling performance of more than 10000 cycles with a capacity retention of 88%, while PPTS suffered a relatively poor rate capability possibly due to its nonconjugated and densely stacked polymer chains that might block the charges transfer . Wu et al introduced two aminotriazole polar groups into 1,4,5,8-naphthalenetetracarboxylic diimide (NTCDI) to synthesize a hydrogen-bonded organic framework (HOF-DAT), which achieved more than 10000 cycles with a capacity retention of 65%, since the formation of multiple hydrogen bonds between intramolecular aminotriazole groups reduced the solubility of HOF-DAT in most organic solvents . Wang et al observed that the introduction of sodium carboxylate could also effectively restrict the dissolution of NTCDI in a diethylene glycol dimethyl ether based electrolyte, which enabled the resulting disodium salt of N , N ′-bis­(glycinyl) naphthalene diimide (Na 2 BNDI) to show a capacity retention of 57.3% after 70000 cycles .…”

“…Wang et al observed that the introduction of sodium carboxylate could also effectively restrict the dissolution of NTCDI in a diethylene glycol dimethyl ether based electrolyte, which enabled the resulting disodium salt of N , N ′-bis­(glycinyl) naphthalene diimide (Na 2 BNDI) to show a capacity retention of 57.3% after 70000 cycles . Although the introduction of polar groups could handle the dissolution issues, these electrochemically inactive polar groups also raised the molecular weights of HOF-DAT and Na 2 BNDI, thus decreasing their specific capacities (143 and 144 mAh g –1 , respectively). , Hence, it is highly desirable to boost the cycling performance of carbonyl-based cathodes without sacrificing their rate capability and specific capacity via structural optimization.…”