ABSTRACT
The performance of electric double-layer capacitors and lithium-ion batteries deteriorates with increasing humidity. The desirable effect of bound water on the energy-storage properties of physically dry cellulose nanofiber (Na-ACF) supercapacitors with sodium (Na) carboxylate radicals was investigated using infrared and near-infrared spectroscopy, and nuclear magnetic resonance spectroscopy, alternating current impedance analyses, and first-principles calculations. The storage capacity decreased gradually upon heating to 423 K and reached zero upon exceeding 483 K, accompanied by increasing electrical resistance, forming a distorted semicircle in Nyquist diagram and drawing the phase angle to zero in Bode diagram. This is attributed to the water in the hydration gel bound to the Na+-ions that cross-link the cellulose chains, evaporating as the temperature increases, and finally becoming Na2O. The increased band-gap energy from the increase in bound water prevents leakage from the supercapacitor. In contrast to ordinary batteries, bound water is necessary for developing Na-ACF supercapacitors.
ABSTRACT
The electric charge storage properties of amorphous cellulose nanofiber (ACF) supercapacitors with different metal carboxylate radicals (COOM; M: Na(I), Ca(II), Al(III)) was investigated in terms of charging/discharging behaviours, alternating current impedance analysis, and plane-wave-based first-principles density functional calculations. Na-ACF exhibited a higher storage effect than Ca- and Al-ACFs. The charge storage mechanism for an Na-ACF supercapacitor was proposed using an electric double layer model in a C12H17O11Na electrolyte with an electrical resistivity of 6.8 × 103 Ω cm, based on the migration of protonic soliton. The supercapacitor, which demonstrated fast charging upon voltage application, could illuminate a white LED for 7 s after charging with 10 mA at 18.5 V.
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).
ABSTRACT
In this study, the electric storage effect of AlO6 clusters in amorphous alumina (AAO) supercapacitors was investigated in terms of cluster morphologies under electron-beam irradiation. Based on first-principles density functional calculation, the optimised structure of AlO6 clusters around an O-vacancy is characterised by a large vacant space created by the absence of an O atom and its neighbouring Al atom. The localised electrons present near the two-atomic vacancies induce positive charges on the inside of the insulating oxide surface, ensuring the adsorption of many electrons on the surface. Electron-beam irradiation (adsorption) from 100 to 180 keV causes the lengths of the Al-O bonds of the cluster to shrink, but then return to the original length with decreasing voltage energy, indicating a rocking-chair-type charge-breathing effect accompanied by a volume expansion of approximately 4%. The I-V and I-R characteristics depicted Coulomb blockade for the switching effect of both the negative and positive potentials. The Ragone plot of the AAO supercapacitor is located at capability area of the second cell.
ABSTRACT
Capacitance distribution of {(Ni(0.6)Nb(0.4)(1-x)Zrx}(100-y)-Hy (x = 0.30, 0.35, 0.40, 0.45 and 0.50, 0 < or = y < or = 20) glassy alloy ribbons was carried out by ac impedance analysis at frequency of 1 kHz, in terms of a distributed constant equivalent circuit. The capacitance can be represented by oblique contour lines. The highest capacitance (1-11 microF) could be found near the point when x = 0.40, y = 10, which is a composition occurring room-temperature Coulomb oscillation, while capacitance of the composition (x = 0.35, y = 4) occurring ballistic transport was around 0.8 microF. The capacitance difference would be explained by an effect of hydrogen localization derived from morphology of distorted Zr-centered icosahedral Zr5Ni5Nb3 clusters and ideal Ni-centered clusters. The electrocapillarity equation showed that the specific capacitance between two electrodes increases parabolic with decreasing the distance, as a polarized glutinous liquid.
