Carbon quantum dot-anchored polyaniline on electrospun carbon nanofibers as freestanding electrodes for symmetric solid-state supercapacitors†

Abstract

A binder-free and freestanding electrode was designed by uniformly immobilizing carbon quantum dot (CQD)-anchored polyaniline (PANI) heterostructures onto electrospun carbon nanofibers (CNFs) via a facile hierarchical assembly process. The fabricated freestanding CNF/PANI/CQD electrode exhibits a unique three-dimensional (3D) network nanostructure, which accelerates ion migration between the interior and surface of the electrode, thereby enhancing its charging and discharging performance. Moreover, the functional groups on the surface of CQDs could anchor PANI through possible chemical bonding, which not only improves the stability of the PANI/CQD heterojunction but also creates an additional conductive channel for the PANI polymer. As expected, the CQD-anchored electrode exhibits a specific capacitance of 756.5 F g⁻¹ at 0.5 A g⁻¹, which is 1.78 times better than the capacitance of CNFs/PANI and 17.4 times higher than that of CNFs. Benefiting from the excellent electrical conductivity and freestanding structure of the electrode, the assembled symmetric solid-state supercapacitor exhibits an excellent capacitance stability rate of 94.69% following 8000 cycles and remains at 81.25% after 10 000 cycles of operation at 1 A g⁻¹. This remarkable cycling durability may be due to the superior 3D network nanostructure and the stable PANI/CQD heterostructure created through chemical bonding. This work offers new design concepts for fabricating binder-free and freestanding electrodes with unique 3D structures for application in other energy storage devices.