Pyridine-Rich Covalent Organic Frameworks as High-Performance\nSolid-State Supercapacitors

Abstract

Covalent\norganic frameworks (COFs), because of their ordered pores\nand crystalline structure, become designable polymers for charge storage\napplications. Supercapacitors are critical in developing hybrid energy\ndevices. Amalgamating these high-surface-area frameworks in the capacitor\nassembly can aid develop robust solid-state supercapacitors. Here,\nwe present supercapacitors drawn on three closely related pyridyl-hydroxyl\nfunctionalized COFs. The keto-enol tautomerism and the hydrogen bonding\nability of the hydroxyl units promise added chemical stability in\nthis potentially hydrolyzable Schiff-bonded COF. Meanwhile, the pyridyl\nand triazine groups ensure rapid charge storage by reversibly interacting\nwith protons from the acidic electrolyte. The COF with the highest\nsurface area, as expected, yields an excellent specific capacitance\nof 546 F/g at 500 mA/g in acidic solution and ∼92 mF/cm² at 0.5 mA/cm² in the solid-state device, which\nis the highest among all the COF-derived solid-state capacitors, which\nis reflected by a high power density of 98 μW/cm² at 0.5 mA/cm², most of which is retained even after 10 000\ncycles. This high activity comes from a smooth electrical-double-layer-capacitance\nfavored by an ordered-porous structure and some pseudo-capacitance\nassisted by the participation of redox-active functional groups. The\nstudy highlights the by-design development of COFs for superior energy/charge\ndevices.