[TPAD-COF] A Redox-Active COFs with Highly Accessible Aniline-Fused Quinonoid Units Affords Efficient Proton Charge Storage

Home > News > [TPAD-COF] A Redox-Active COFs with Highly Accessible Aniline-Fused Quinonoid Units Affords Efficient Proton Charge Storage

Abstract:
This article, titled "A Redox-Active Covalent Organic Framework with Highly Accessible Aniline-Fused Quinonoid Units Affords Efficient Proton Charge Storage," investigates a novel cathode material based on a redox-active 2D covalent organic framework (TPAD-COF) for aqueous proton batteries. The study addresses the challenges of electrode material corrosion and dissolution in acidic electrolytes, presenting a material with high capacity, long-term cycling stability, and excellent stability in acidic environments. The TPAD-COF cathode delivers a high capacity of 126 mAh g⁻¹ at 0.2 A g⁻¹ and retains 84% of its capacity after 5000 cycles at 2 A g⁻¹. Comprehensive studies reveal the redox activity of the aniline-fused quinonoid units, making TPAD-COF a promising candidate for aqueous proton batteries.

Research Background:
1.Global Energy Challenges and Environmental Concerns: With the increasing severity of environmental problems and the depletion of fossil fuels, there is a growing need for eco-friendly, cost-efficient, and intrinsically safe energy storage solutions. Aqueous batteries have emerged as a promising alternative due to their sustainability and safety.
2.Limitations of Traditional Electrode Materials: Most metal oxides and small organic molecules exhibit poor long-term stability due to corrosion or dissolution in acidic electrolytes. While some polymers can overcome dissolution issues, their low porosity leads to poor mass transport and swelling/shrinkage during charge/discharge cycles, shortening device lifetimes.
3.Innovative Approach by the Authors: The authors propose a redox-active 2D covalent organic framework (TPAD-COF) with aniline-fused quinonoid units. This material combines the advantages of high proton conductivity, excellent stability in acidic environments, and multiple redox-active centers, addressing the limitations of traditional electrode materials.

Experimental Section:
1.Synthesis of TPAD-COF:
1) Polycondensation of 1,4,5,8-tetrakis((4-(5,5-dimethyl-1,3-dioxan-2-yl)phenyl)amino)anthracene-9,10-dione (TPAD-DMO) and 1,4,5,8-tetrakis((4-aminophenyl)amino)anthracene-9,10-dione (TPAD-NH2) under solvothermal conditions.
2) The mixture was sonicated, degassed, and heated at 120 °C for 3 days.
3) The resulting dark green precipitate was filtered, washed, and dried to obtain TPAD-COF.
   -Results: The successful synthesis of TPAD-COF was confirmed by FT-IR, solid-state ¹³C NMR, and PXRD measurements.

2.Characterization of TPAD-COF:
   -PXRD: The pattern exhibited intense peaks corresponding to the (110), (200), (210), (220), (330), and (001) planes, indicating an eclipsed AA stacking structure.
   -BET Surface Area: The BET surface area was 1080 m² g⁻¹, with a dominant pore size of 1.72 nm.
   -SEM and TEM: TPAD-COF displayed a rod-like morphology with clear lattice fringes of the (200) planes.
   -TGA: TPAD-COF exhibited high thermal stability with only 5% initial mass loss at 450 °C under a nitrogen atmosphere.

3.Electrochemical Performance:
   -Cyclic Voltammetry (CV): The CV curve revealed multiple redox couples within 0–0.9 V, indicating fast reaction kinetics.
   -Galvanostatic Charge/Discharge: TPAD-COF delivered capacities of 126, 100, 77, and 73 mAh g⁻¹ at current densities of 0.2, 0.5, 2, and 6 A g⁻¹, respectively.
   -Cycling Stability: The capacity retention was 84% after 5000 cycles at 2 A g⁻¹, demonstrating excellent long-term stability.

4.Full Battery Assembly:
   -TPAD-COF//AQ Battery: An all-organic proton battery was assembled with TPAD-COF as the cathode and anthraquinone (AQ) as the anode.
   -Performance: The battery delivered a discharge capacity of 115 mAh g⁻¹ at 0.5 A g⁻¹ after 130 cycles, showcasing potential for practical applications.

Analysis and Testing:
1.FT-IR and XPS:
   -FT-IR: Reversible changes in the stretching vibrations of C=O, C=N, C–N, and C–O groups confirmed the redox activity of the aniline-fused quinonoid units.
   -XPS: The presence of C–O, O–H, C–N, and N–H peaks indicated the storage and release of H⁺ ions during charge/discharge processes.

2.Electron Paramagnetic Resonance (EPR):
   -EPR: The appearance and disappearance of EPR signals during charging and discharging confirmed the redox mechanism involving the C–OH group.

3.Liquid-State ¹H NMR:
   -¹H NMR: The integration of protons at 11.82 ppm increased during discharge, confirming the formation of C–OH moieties and the reversible redox activity of the TPAD core.

4.Density Functional Theory (DFT) Calculations:
   -Molecular Electrostatic Potential (MESP): The C=O and C=N groups exhibited negative MESP values, indicating their redox activity for H⁺ uptake.
   -Reaction Pathways: Calculations proposed a three-step reaction mechanism involving the reduction of N and O atoms in the TPAD unit during discharge.

Summary
The study successfully developed a redox-active TPAD-COF with densely distributed aniline-fused quinonoid units as a cathode material for aqueous proton batteries. The material exhibited high capacity, excellent cycling stability, and superior stability in acidic environments. The TPAD-COF//AQ all-organic proton battery demonstrated long-term cycling stability and high discharge capacity, highlighting its potential for practical applications. This research broadens the scope of electrode materials for aqueous proton batteries and provides a new direction for designing materials with durable cycling performance.

Outlook:
1.Long-Term Testing: Further testing of the TPAD-COF material in more complex and longer-term environments to assess its practical feasibility.
2.Scalability: Exploration of scalable synthesis methods to reduce production costs and facilitate commercialization.
3.Material Optimization: Continued optimization of the TPAD-COF structure to enhance its performance and stability in various conditions.

A Redox-Active Covalent Organic Framework with Highly Accessible Aniline-Fused Quinonoid Units Affords Efficient Proton Charge Storage
Authors: Xiaoli Yan, Feixiang Wang, Xi Su, Junyu Ren, Meiling Qi, Pengli Bao, Weihua Chen, Chengxin Peng, Long Chen
DOI: 10.1002/adma.202305037
Link: https://onlinelibrary.wiley.com/doi/10.1002/adma.202305037

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