Amorphous cellulose nanofiber supercapacitors

Abstract

Despite the intense interest in cellulose nanofibers (CNFs) for biomedical and engineering applications, no research findings about the electrical energy storage of CNF have been reported yet. Here, we present the first electroadsorption effects of an amorphous cellulose nanofiber (ACF) supercapacitor, which can store a large amount of electricity (221 mJm^-2, 13.1 Wkg^-1). The electric storage can be attributed to the entirely enhanced electroadsorption owing to a quantum-size effect by convexity of 17.9 nm, an offset effect caused by positive polar C₆=O₆ radicles, and an electrostatic effect by appearance of the localised electrons near the Na ions. The supercapacitor also captures both positive and negative electricity from the atmosphere and in vacuum. The supercapacitor could illuminate a red LED for 1 s after charging it with 2 mA at 10 V. Further gains might be attained by integrating CNF specimens with a nano-electromechanical system (NEMS).

Figure 1

(a) Discharging behaviours of the ACF device for constant currents of 20 nA, 100 nA, 500 nA, 2.5 μA, and 12.5 μA after 2 mA–10 V charging for 50 s. (b) Discharging time and IR drop for 2 mA-rapid charging/1μA-discharging up to 30 times. (c) Applied voltage dependency of stored energy. (d) An LED powered by the ACF device.

Figure 2

Non-destructive analysis of the electrostatic contribution of the specimen. (a) Nyquist plot as a function of frequency for the ACF device. (b) Real and imaginary impedances. (c) Frequency dependence of phase angle and series capacitance. (d) I–V and R–V characteristics between − 200 and + 200 V.

Figure 3

(a) XRD analysis of ACF specimen. (b) Changes in atomic pair distribution functions (PDFs) under 100–200 kV irradiation at a rate of 3 nA/m². (c) Change rates of bonding distance as functions of applied voltage. (d) AFM image of the ACF surface. (e) Histogram of the potential distribution at + 40 V. Inset in (a) SAED pattern, (d) three-dimensional AFM image, (e) electrostatic potential distributions for ACF surface when the applied voltage changed from − 20 V to + 40 V.

Figure 4

(a) Structure of sodium (1→4)-β-D-poly-glucuronate cell with green carbon, pink oxygen, light-blue hydrogen, and red sodium atoms. (b) Schematic diagram for calculations based on the Thomas–Fermi statistical method. (c) Convex dependences of the electrostatic potential and electron pressure with diameter. (d) Schematic representation of the microscopic electric energy storage used in this study. (e) The electric distributed constant circuit of the amorphous ACF surface.

Figure 5

Local structures and density of states (DOS) in C₁₂H₂₀O₁₀ and C₁₂H₁₇O₁₁Na. Isolated electronic state (yellow) locally occurs in vicinity of Na ion.