Exfoliated Mesoporous 2D Covalent Organic Frameworks for High-Rate Electrochemical Double-Layer Capacitors

The electrochemical double-layer capacitors (EDLCs) are highly demanded electrical energy storage devices due to their high power density with thousands of cycle life compared with pseudocapacitors and batteries. Herein, a series of capacitor cells composed of exfoliated mesoporous 2D covalent organic frameworks (e-COFs) that are able to perform excellent double-layer charge storage is reported. The selected mesoporous 2D COFs possess eclipsed AA layer-stacking mode with 3.4 nm square-like open channels, favorable BET surface areas (up to 1170 m² g^-1 ), and high thermal and chemical stabilities. The COFs via the facile, scalable, and mild chemical exfoliation method are further exfoliated to produce thin-layer structure with average thickness of about 22 nm. The e-COF-based capacitor cells achieve high areal capacitance (5.46 mF cm^-2 at 1,000 mV s^-1 ), high gravimetric power (55 kW kg^-1 ), and relatively low τ₀ value (121 ms). More importantly, they perform nearly an ideal DL charge storage at high charge-discharge rate (up to 30 000 mV s^-1 ) and maintain almost 100% capacitance stability even after 10 000 cycles. This study thus provides insights into the potential utilization of COF materials for EDLCs.