Polydopamine-Functionalized Porous Carbon Nanofibers Derived from Bacterial Cellulose for Supercapacitors

In this work, we describe a facile and eco-friendly method rationally designed to synthesize N-containing carbon nanofibers from polydopamine (PDA)-decorated bacterial cellulose (BC) nanofibers using freeze-drying and carbonization processes. The poor electrical conductivity of the pristine bacterial cellulose-derived carbon nanofiber (BCNF-0) limits its performance in supercapacitor applications. This may be overcome by this promising strategy, without any metal doping and only by surface modification of BC nanofibers with a coating of PDA in an alkaline medium. The optimized PDA-coated carbon, BCNF-2, with a surface area of 353 m2/g and 3.9 and 5.6 atom % of N and O, respectively, exhibits good electrochemical performance. The BCNF-2 electrode delivers a significant specific capacitance of 536 F/g, an energy density of 60.3 Wh/kg, and a power density of 450.4 W/kg at a current density of 1 A/g in a 1 M H2SO4 electrolyte. It also shows high cyclic stability; after 5000 cycles, the capacitance retention is 106%, which indicates notable robustness of the electrode material. A solid-state symmetric supercapacitor designed from BCNF-2 using a PVA/H2SO4 gel electrolyte gives a capacitance of 123 F/g at a current density of 0.2 A/g. The device shows significant Coulombic efficiency of ca. 89% after 1500 cycles. A mass loading of 3.25 mg/cm2 is capable of lighting a 3 V green light-emitting diode bulb for 8 min. This metal-free approach to fabricate electrodes from an inexpensive green source is a step forward to sustainable and high-performance bioengineered energy storage technologies.