Pyrene-Linked Covalent Organic Polymer/Single-Walled Carbon Nanotubes Hybrids as High-Performance Electrodes for Supercapacitive Energy Storage

Abstract

Among energy storage devices, covalent organic polymers (COPs) are the prime choice as active electrode materials, which are held together by strong covalent bonds and offer notable advantages such as high specific surface area and exceptional chemical durability. However, certain COPs have limited conductivity and underwhelming electrochemical properties, which hinders their application in supercapacitors (SCs). To address these challenges, we successfully synthesized two types of porous organic polymers, PyTB-BBT COP and PyTB-Py COP, along with graphene oxide (GO) and single-walled carbon nanotubes (SWCNTs) named PyTB-BBT COP/GO, PyTB-BBT COP/SWCNTs, PyTB-Py COP/GO and PyTB-Py COP/SWCNTs, respectively via physical interaction [π–π stacking interactions]. The PyTB-BBT COP and PyTB-Py COP were initially prepared through a Schiff base reaction, using 4,4′,4″,4‴-(pyrene-1,3,6,8-tetrayltetrakis(ethyne-2,1-diyl))tetraaniline (PyTB-4NH₂) as a building block, which was reacted with 4,4′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzaldehyde (BBT-2CHO) for PyTB-BBT COP, and with 4,4′,4″,4‴-(pyrene-1,3,6,8-tetrayl)tetrabenzaldehyde for PyTB-Py COP. The successful synthesis of PyTB-BBT COP/GO, PyTB-BBT COP/SWCNTs, PyTB-Py COP/GO, and PyTB-Py COP/SWCNTs through π–π stacking interactions were verified using TEM and photoluminescence (PL) measurements. Notably, compared to their pristine counterparts, as well as PyTB-BBT COP/GO (5 wt %) and PyTB-Py COP/GO (5 wt %), the PyTB-BBT COP/SWCNTs (5 wt %) and PyTB-Py COP/SWCNTs (5 wt %) hybrids demonstrate remarkable promise as supercapacitor electrode materials. They exhibit specific capacitances of 185 and 342 F g^–1 at a current density of 0.5 A g^–1, retaining approximately 85% and 92% of their capacity after 10,000 cycles in a three-electrode supercapacitor setup. The outstanding electrochemical performance of the PyTB-Py COP/SWCNTs (5 wt %) hybrid could be caused by three key elements: strong π–π stacking interactions of SWCNTs and PyTB-Py COP, facilitated by the presence of two pyrene units in the PyTB-Py COP framework; the porous structure of PyTB-Py COP, which improves ion transport; and the excellent electron conductivity provided by the SWCNTs.