(546g) Highly Flexible, Strong and Conductive Cellulose Nanofibrils/PEDOT:PSS Nanopapers for All-Solid-State Supercapacitors

Recently, cellulose nanofibrils (CNF) produced from cellulosic materials (e.g. wood, agricultural and industrial waste, etc.) have received increasing attention due to their unique properties such as high specific surface area, high elastic modulus, high thermal stability, as well as renewability and biodegradability. These unique properties make CNF as promising building blocks for the manufacture of many sustainable nanomaterials.

In this work, we firstly prepared CNF from pulp mill sludge by a sustainable process of formic acid (FA) hydrolysis pretreatment and the followed microfluidization. It was found that the mild FA hydrolysis (at 95 ºC for 3-6 h) pretreatment could hydrolyze most of hemicellulose, swell and break down the cellulose fibers, and the collected cellulosic solid residue with a high yield (over 75%) could be further converted to CNF with relatively low-intensity microfluidization (only two passes). Then, the CNF was coated with PEDOT:PSS via in situ polymerization. Afterwards, flexible and conductive CNF/PEDOT:PSS nanopapers were prepared from the above obtained PEDOT:PSS-coated CNF suspension by a simple vacuum filtration approach. Furthermore, CNF/PEDOT:PSS nanopapers were treated with dimethyl sulfoxide (DMSO) to increase the conductivity. Results showed that the DMSO-treated CNF/PEDOT:PSS nanopapers had high tensile strength (over 60 MPa), high thermal stability, and low sheet resistance (18 Ω sq^-1). Finally, a symmetric all-solid-state supercapacitor was assembled using the DMSO-treated CNF/PEDOT:PSS nanopapers as electrodes. It was found that the assembled supercapacitor could deliver the maximum areal specific capacitance of 888.7 mF cm^-2 (corresponding to 111.1 F cm^-3) and offer the highest areal energy density of 79.0 μWh cm^-2 (corresponding to 9.9 mWh cm^-3), which are among the highest values reported for PEDOT:PSS based supercapacitors. More importantly, the assembled supercapacitor showed remarkable cycling stability with the capacitance retention of 109.5% after 10,000 charge/discharge cycles at a current density of 20 mA cm^-2. Considering the sustainable and facile preparation process and excellent electrochemical performance, the obtained CNF/PEDOT:PSS nanopapers could be a promising candidate for flexible energy storage devices.