Mechanically Robust and Highly Conductive Cellulose Nanopaper Electrodes Enabled by Polyaniline-Graphene Hybrid Networks for Flexible Supercapacitors

Flexible, freestanding electrodes with high mechanical robustness, electrical conductivity, and electrochemical performance are highly desirable for wearable energy storage devices. Herein, a hierarchical polyaniline/partially oxidized graphene/cellulose nanopaper (PANI/po-Gr/CNP) electrode was developed by integrating redox-active PANI, conductive po-Gr, and mechanically robust cellulose nanofibers (CNFs). PANI-coated CNFs were first prepared via in situ polymerization, followed by incorporation of po-Gr nanosheets. We vacuum-filtered and dried the resulting hybrid suspension to fabricate a freestanding PANI/po-Gr/CNP electrode. Compared with the po-Gr-free PANI/CNP electrode, the optimized PANI/po-Gr/CNP electrode increased electrical conductivity from 0.16 to 1.85 S·cm–1 while maintaining a comparable tensile strength (∼42 MPa). In a three-electrode configuration, the optimized electrode delivered an areal capacitance of 2.74 F·cm–2 at 5 mV·s–1, corresponding to volumetric and gravimetric capacitances of 342.5 F cm–3 and 572.7 F·g–1 (based on the combined mass of PANI and po-Gr), respectively. The assembled symmetric supercapacitor delivered an areal energy density of 58.08 μWh·cm–2 and a volumetric energy density of 7.26 mWh·cm–3, while retaining 81.0% of its initial capacitance after 10,000 charge–discharge cycles. These results show that combining CNFs, PANI, and po-Gr enables a freestanding electrode with a favorable balance of mechanical robustness, electrical conductivity, and electrochemical performance, offering a promising platform for flexible, wearable supercapacitors.