Development of Triazine-Based Covalent Organic Frameworks for Enhanced Electrochemical Energy Storage Applications

Abstract

Herein, two distinct porous covalent organic frameworks (COFs) were developed by polycondensation of a heteroatom-rich rigid triazine-based triamine linker, namely, 5,5',5''-(1,3,5-triazine-2,4,6-triyl)tris(pyridin-2-amine) (TPA), with two structurally flexible aldehyde linkers. Two dissimilar aldehyde linkers, 4,4',4''-((1,3,5-triazine-2,4,6-triyl)tris(oxy))tribenzaldehyde (TPT-CHO) and 2,4,6-tris-(2-methoxy-4-formyl-phenoxy)-1,3,5-triazine (TMPT-CHO), were chosen on the basis of the impact of incorporating methoxy groups and varying heteroatom contents within the monomers, leading to the synthesis of two diverse COF materials named as TPTTPA-COF and TMPTTPA-COF. The incorporation of methoxy (-OCH3) functional groups in TMPTTPA-COF was aimed at enhancing redox activity, while the higher surface area of TPTTPA-COF (207.71 m2 g-1 vs. 104.85 m2 g-1 for TMPTTPA-COF) was expected to facilitate superior charge storage. Electrochemical investigations in a three-electrode setup demonstrated that TPTTPA-COF exhibited a specific capacitance of 277.5 F g-1 at 5 mV/s and 347 F g-1 at 0.5 A g-1, primarily governed by an electric double-layer capacitance (EDLC) mechanism. In contrast, TMPTTPA-COF displayed superior capacitance 382 F g-1 at 5 mV/s and 383 F g-1 at 1 A g-1 due to additional pseudocapacitive contributions from methoxy (-OCH3) groups. Computational analysis revealed a lower bandgap for TMPTTPA-COF compared to TPTTPA-COF, which correlates with improved electronic conductivity and charge transfer kinetics. Cycling stability studies demonstrated excellent capacitance retention, with TPTTPA-COF retaining 90% and TMPTTPA-COF retaining 91% of their initial capacitance after 10,000 cycles, alongside coulombic efficiencies of 94% and 95%, respectively.