Pyridine-Rich Covalent Organic Frameworks as High-Performance Solid-State Supercapacitors

Covalent organic frameworks (COFs), because of their ordered pores and crystalline structure, become designable polymers for charge storage applications. Supercapacitors are critical in developing hybrid energy devices. Amalgamating these high-surface-area frameworks in the capacitor assembly can aid develop robust solid-state supercapacitors. Here, we present supercapacitors drawn on three closely related pyridyl-hydroxyl functionalized COFs. The keto-enol tautomerism and the hydrogen bonding ability of the hydroxyl units promise added chemical stability in this potentially hydrolyzable Schiff-bonded COF. Meanwhile, the pyridyl and triazine groups ensure rapid charge storage by reversibly interacting with protons from the acidic electrolyte. The COF with the highest surface area, as expected, yields an excellent specific capacitance of 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 is the highest among all the COF-derived solid-state capacitors, which is reflected by a high power density of 98 μW/cm2 at 0.5 mA/cm2, most of which is retained even after 10 000 cycles. This high activity comes from a smooth electrical-double-layer-capacitance favored by an ordered-porous structure and some pseudo-capacitance assisted by the participation of redox-active functional groups. The study highlights the by-design development of COFs for superior energy/charge devices.