Synthesis of SulfonylTwo-Dimensional Covalent OrganicFrameworks for Supercapacitor Applications

Covalent organic frameworks (COFs) are attracting more attention for energy storage applications. COFs possess unique structural properties, such as highly ordered pore structures, abundant functionalization sites, and tunable chemical properties, making them ideal candidates for the development of novel energy storage materials. In this work, we synthesized sulfonyl two-dimensional (2D) covalent organic frameworks (SLD-COFs) using 4,4′-sulfonyldiphenylamine (SLD). SLD-COFs have a remarkable conjugated structure, which includes imine groups forming large π-bonds, and the conjugated structure can provide consecutive electron conduction paths, which enables SLD-COF to transfer charges more efficiently, thus improving the electrical conductivity. Additionally, the sulfonyl groups introduce redox-active sites, which participate in the redox process during electrochemical reactions and generate a pseudocapacitive effect. For a current of 0.5 A/g, the specific capacitance of the SLD-COF material was 31.5 F/g in an acidic electrolyte and 41.7 F/g in an alkaline electrolyte. The structural flexibility and good electrochemical properties of the COFs make them a potentially essential component of energy storage applications. Meanwhile, the capacitance retention of SLD-COFs reaches 78.3% after 1000 GCD cycles at a current density of 1 A/g, which indicates its good cycling stability.