Surface engineering of carbon nanotube films via pyrene grafting for high-performance flexible supercapacitors

The performance of carbon nanotube (CNT)-based supercapacitors has been limited by their low surface area and lack of redox-active sites. Herein, we present a simple and scalable method to functionalize single-walled CNTs with pyrene moieties through radical grafting, enabled by thermal desulfonation of sulfonated pyrene. To enhance grafting efficiency, CNTs were intentionally shortened, increasing the number of reactive ends. The resulting pyrene-grafted short CNTs (PYgSCNTs) exhibited increased surface area and redox functionality without compromising the intrinsic electrical and mechanical properties of CNTs. Morphological and structural analyses confirmed successful grafting and formation of mesoporous structures. Electrochemical characterization revealed that PYgSCNT films deliver significantly improved capacitance, achieving a specific capacitance of 59.2 F g⁻¹, excellent rate capability, and stable cycling over 2000 cycles. A flexible supercapacitor device fabricated using PYgSCNT films as electrodes demonstrated a high volumetric energy density of 8.9 mW h cm⁻³ and power density of 878 mW cm⁻³, surpassing the performance of conventional CNT-containing devices. This work offers a non-destructive, solution-processable approach for surface engineering of CNTs, opening new avenues for the development of high-performance, flexible energy storage systems.