Tuning carbon nanotube-based buckypaper properties by incorporating different cellulose nanofibrils for redox supercapacitor electrodes

Abstract

In recent years, supercapacitors (SCs) that employ redox electrolytes have stood out as a simple technology that allows maximizing the energy density of this class of devices. However, there is a growing demand for integrable devices, and few studies focus on obtaining moldable, thin, and flexible electrode materials with a high capacity to electrosorb the redox additives from the electrolyte. In this work, we report the preparation of buckypapers (BPs) composed of few-walled carbon nanotubes (FWCNT) and different cellulose nanofibrils (CNF) for application as flexible and foldable redox SC electrodes. Thus, we aim to demonstrate and discuss how different CNFs affect the hydrophilicity, mechanical strength, electrical conductivity, textural properties, and electrochemical performance of BPs immersed in an electrolyte containing the [Fe(CN)₆]4−/[Fe(CN)₆]3− redox couple. For this, three different sources of cellulose were used for the preparation of CNFs with dimensions less than 100 nm in diameter and lengths in the order of hundreds of micrometers: Eucalyptus sp, Pinus sp, and Bambusa vulgaris. Our results reveal that more hydrophobic CNFs (mainly from Bambusa vulgaris) favor the formation of stronger interactions in networks with FWCNTs, promoting the highest increases in maximum strain (215%), and the highest specific capacitances (167.6 F g−1 at 4.42 mA cm−2). Finally, this work demonstrates that CNFs can be used not only as ligands but as active components that allow optimizing several properties of BPs and their performance as redox SC electrodes.