Thiol-decorated covalent organic frameworks as multifunctional materials for high-performance supercapacitors and heterogeneous catalysis

Abstract

Tunable physicochemical properties combined with the high chemical and thermal stabilities of covalent organic frameworks (COFs) make them ideal candidates for the next generation of energy storage systems. The integration of redox-active moieties (e.g., thiols) in COFs imparts them a pseudocapacitive characteristic and represents an efficient strategy to boost their performance as electrochemical supercapacitors (SCs). We report the synthesis of two thiol-decorated COFs (SH-COF-1 and SH-COF-2) via the condensation between 2,5-diaminobenzene-1,4-dithiol (DABDT) and benzene-1,3,5-tricarboxaldehyde (TBA), or 1,2,4,5-tetrakis-(4-formylphenyl)benzene (TFPB), respectively. SH-COF-1, which possesses a higher number of thiol groups per structural repeat unit compared to SH-COF-2, exhibits a higher surface area (227 m² g⁻¹) and enhanced electrochemical performance (areal capacitance of 118 mF cm⁻² and a capacitance retention >95% after 1000 cycles), being superior to previously reported COFs missing redox-active units in their scaffolds. Moreover, to demonstrate the multifunctionality resulting from the presence of thiol groups, AuNPs were in situ grown using SH-COFs as templates. By taking advantage of the strength of the bonding between the AuNPs and the SH-COFs, Au-SH-COF hybrids were used as heterogeneous catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), showing an excellent catalytic activity k_obs, of 1.01 min⁻¹ and 0.71 min⁻¹ for Au-SH-COF-1 and Au-SH-COF-2, respectively, and long-term performance (4-NP to 4-AP conversion above 95% after 10 catalytic cycles). This work highlights the importance of COFs' molecular design towards the development of highly efficient (multi)functional materials.