[AAm-TPB] Arylamine-Linked 2D Covalent Organic Frameworks for Efficient Pseudocapacitive Energy Storage

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Abstract:
The development of new linkages is a crucial strategy to enrich the diversity of covalent organic frameworks (COFs). This study introduces a novel arylamine linkage for constructing COFs, resulting in two new materials—AAm-TPB and AAm-Py. These COFs exhibit high stability and excellent pseudocapacitive energy storage performance, with AAm-TPB achieving a remarkable capacitance of 271 Fg⁻¹ at a discharge rate of 1 Ag⁻¹. The study highlights the potential of arylamine-linked COFs for high-performance energy storage applications.

Research Background:
1. Energy Storage Challenges:
   - The increasing demand for sustainable energy storage solutions has driven the search for materials with high energy density and stability.
   - Traditional energy storage materials often face limitations in terms of capacitance, stability, and cost-effectiveness.
2. Existing Solutions:
   - Researchers have explored various materials, including conductive polymers like polyaniline (PANI), for their high capacitance and conductivity.
   - COFs have emerged as promising candidates due to their tunable structures and properties, but the development of new linkages remains a challenge.
3. Innovative Approach:
   - The authors propose a new arylamine linkage, inspired by the electroactive diphenylamine moieties in PANI, to construct COFs.
   - This linkage not only enhances stability but also maintains high conjugation, beneficial for electrical conduction and redox activity.

Experimental Section:
1. Synthesis of Model Compound DATP:
   - Steps:
     1. Aniline and dimethyl succinyl succinate (DMSS) were reacted in the presence of p-toluenesulfonic acid (PTSA) in a mixed solvent of o-dichlorobenzene (o-DCB) and n-butanol (n-BuOH) at 120°C for 1 day.
     2. The mixture was cooled, poured into water, and extracted with ethyl acetate. The product was recrystallized from dichloromethane (DCM) and petroleum ether (PE).
   - Result: The model compound DATP was obtained as a pink powder with a yield of 90%.
2. Synthesis of AAm-TPB:
   - Steps:
     1. TPB-NH₂ and DMSS were reacted under similar conditions to form pre-AAm-TPB.
     2. Pre-AAm-TPB was oxidized in trifluoroacetic acid (TFA) at 50°C for 24 hours to form AAm-TPB.
   - Result: AAm-TPB was obtained as a deep-red powder with a yield of 95%.
3. Synthesis of AAm-Py:
   - Steps:
     1. Py-NH₂ and DMSS were reacted to form pre-AAm-Py.
     2. Pre-AAm-Py was oxidized in TFA to form AAm-Py.
   - Result: AAm-Py was obtained as a deep-orange powder with a yield of 94%.

Analysis and Testing:
1. Fourier Transform Infrared (FT-IR) Spectroscopy:
   - Results:
     - Characteristic N-H stretching bands and C=O stretching modes disappeared in both COFs, indicating high condensation efficiency.
     - New stretching bands for secondary amines appeared, confirming the formation of arylamine linkages.
2. Solid-State ¹³C CP/TOSS NMR Spectroscopy:
   - Results:
     - The NMR spectra of AAm-TPB and AAm-Py were similar to the model compound DATP, confirming the absence of imine linkages.
3. UV-Vis Spectroscopy:
   - Results:
     - Both COFs exhibited broad absorption from 300 to 800 nm, indicating improved conjugation and narrower optical band gaps (1.96 eV for AAm-TPB and 1.97 eV for AAm-Py).
4. Powder X-ray Diffraction (PXRD):
   - Results:
     - The PXRD patterns of AAm-TPB and AAm-Py matched well with the simulated eclipsed AA-stacking modes.
     - AAm-TPB had a BET surface area of 403 m²g⁻¹, and AAm-Py had a BET surface area of 285 m²g⁻¹.
5. Thermogravimetric Analysis (TGA):
   - Results:
     - Both COFs exhibited weight loss starting at around 240°C, indicating moderate thermal stability.
6. Electrochemical Testing:
   - Results:
     - AAm-TPB showed a high gravimetric capacitance of 271 Fg⁻¹ at 1 Ag⁻¹ and retained 91% of its capacitance after 10,000 cycles.
     - The AAm-TPB//AC asymmetric supercapacitor achieved a maximum energy density of 19.16 Whkg⁻¹ and power density of 350 Wkg⁻¹.

Conclusion:
The study successfully developed a new arylamine linkage for constructing COFs, resulting in materials with high stability and excellent pseudocapacitive energy storage performance. AAm-TPB exhibited a remarkable capacitance of 271 Fg⁻¹, making it one of the highest among reported COF-based electrode materials. The intralayer hydrogen bonding in the COFs contributed to their high stability and improved electron transfer kinetics. This work opens new avenues for the development of COF-based materials for high-performance energy storage applications.

Arylamine-Linked 2D Covalent Organic Frameworks for Efficient Pseudocapacitive Energy Storage
Authors: Zongfan Yang, Jingjuan Liu, Yusen Li, Guang Zhang, Guolong Xing, Long Chen
DOI: 10.1002/anie.202108684
Article Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.202108684

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