Nanocrystalline Cellulose Confined in Amorphous Carbon Fibers as Capacitor Material for Efficient Energy Storage

The development of sustainable and renewable energy storage systems is a promising approach toward steady and reliable energy supply. In this study, cellulosic palm loofah fibers were used as a precursor to produce amorphous carbon (Am-C) with retained crystalline cellulosic planes via a simple activation method. The Am-C exhibits a fairly high BET surface area of 2000 m2/g and a 3D-microporous structure with small mesopores. The symmetric Am-C//Am-C supercapacitor device tested in 1.0 M NaCl aqueous electrolyte showed specific capacitances of 201 F/g at 5 mV/s and 337 F/g at 1 A/g. The device exhibits a stable performance across a potential window of 1.8 V with ultrahigh energy and power densities of 51.4 Wh/kg at 4.5 kW/kg and 16.95 Wh/kg at 18 kW/kg. The device showed extraordinary increasing capacitive behavior upon cycling at 10 A/g for over 25000 cycles. The exceptional device performance could be ascribed to the electrochemical graphitization during long-term cycling together with the enhanced wettability as confirmed via Raman, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), and contact angle measurements.