(546g) Highly Flexible, Strong and Conductive Cellulose Nanofibrils/PEDOT:PSS Nanopapers for All-Solid-State Supercapacitors
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 Î© 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 Î¼Wh 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.