Buckypapers of carbon nanotubes and cellulose nanofibrils: Foldable and flexible electrodes for redox supercapacitors

Abstract

In this work, we report a buckypaper composite with properties suitable for high performance electrodes of redox supercapacitors. The synthesis employs a specific combination of the double- and triple-walled carbon nanotubes (FWCNT) with cellulose nanofibrils (CNF), with dimensions of 20–50 nm in width and lengths of up to several hundred microns. The generated composite (BP/CNT@CNF) preserves the structure of the FWCNTs and ensures greater wettability, without significant damage to electrical conductivity. When compared to a buckypaper produced without CNF, BP/CNT@CNF is completely moldable and flexible, with an increase of about 375% in tensile strength, and 400% in the maximum strain. As electrodes, BP/CNT@CNF is stable in different aqueous redox electrolytes at different pHs containing hydroquinone (HQ in 1.0 M H2SO4), potassium hexacyanoferrate(II) (K₄[Fe(CN)₆] in 3.0 M KOH) and KBr in neutral medium. In all media, excellent capacitance retentions are obtained, evaluated in 12,000 cycles. The best electrochemical performances are obtained with HQ/H2SO4 as a redox electrolyte. High specific capacitance values are found from 1 A g−1 (380.8 F g−1) to 15 A g−1 (216.1 F g−1), with energy and power densities corresponding to 28.2 W h kg−1 and 3974.7 W kg−1, respectively, calculated at electrode level.