Redox-Active Microporous Covalent Organic Frameworks for Additive-Free Supercapacitors.

Abstract

2D covalent organic frameworks (COFs) have garnered significant attention by virtue of their porous nature, structural tunability, and ability to incorporate highly reversible redox-active groups. These characteristics qualify them for a range of energy storage devices, including supercapacitors, which can assume a pivotal role towards attaining a more sustainable future amid escalating energy needs. Herein, two 2D COFs are reported containing wurster (W) and pyrene (PY) units, WW COF and WPy-I COF, which demonstrate reversible redox behavior and characteristic pseudocapacitance. Both COFs exhibit high crystallinity demonstrated with X-ray diffraction analysis, exhibiting a thermal dependence of the intralayer bonding and interlayer stacking arrangement from WPy-I toward WPy-II COFs. Additionally, the WW and WPy-I COFs were grown on glass and stainless-steel meshes (SSMs) featuring different surface coatings. These coated SSMs proved suitable as current collectors for testing the COFs regarding their specific capacitance, without the need to add any conducting additives, revealing a promising capacitance of 48.9 F g^-1 for the WW COF. Moreover, these electrodes can be applied in symmetrical supercapacitor devices with an ionic liquid serving as electrolyte. The remarkable performance of the redox-active Wurster unit identifies it as a promising building motif for COFs with high specific capacitance, even in devices devoid of carbon additives.