The Synthesis and Characterization of Bioactive Carbon Material Supercapacitor Loaded with Nickel Hydroxide
Supercapacitor is an environmentally friendly energy storage device, which fills the gap between traditional capacitors and batteries, and its energy density and power density are higher than the battery [1]. Moreover, the supercapacitor has the characteristics of high charging and discharging efficiency and long cycle life. This makes it used in the electric vehicles, high powered weapons, standby power in electronic equipment, flash of industrial equipment and ignition device [2]. So it has great significance for the basic research, the development of electronic industry and the electric vehicle to carry out the supercapacitor electrode materials [3]. Here, we firstly prepared the activated carbon materials by carbonizing, activating the biological material, then prepared the nickel hydroxide/activated carbon composites by direct precipitation method, and studied the electrochemical properties of composite materials with different nickel hydroxide (Ni(OH)2) contents (the mass fraction). The results of cyclic voltammetry and constant current charge-discharge are that a small amount of Ni(OH)2 are mixed in the carbon surface and pores, the composite material has a good specific capacitance, stability, charging and discharging performance compared with the activated carbon. When the mass fraction of Ni(OH)2 is 12%, the supercapacitor exhibits the excellent electrochemical properties, its capacitance is up to 400.78F/g which improved 75.21% compared with the activated carbon’s capacitance (228.74F/g). 6mol/L potassium hydroxide (KOH) is used as an electrolyte, the capacitance is only reduced to 94.42% after conducting 1000 times cycle life tests. This means that the supercapacitor shows a good stability.
A comparative study of activated carbon-based symmetric supercapacitors in Li2SO4 and KOH aqueous electrolytes
In this work, we have prepared activated carbon (AC)-based symmetric supercapacitor (SC) using Li2SO4 aqueous electrolyte instead of H2SO4 and KOH and obtained a device with an improved cell voltage window (CVW) of 0 − 1.6 V from 0 to 1.0 V. The SC using KOH electrolyte is also fabricated for comparison. The electrochemical characteristics of SCs such as cyclic voltammetry (CV), galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) and cycle stability are investigated systematically. The possible redox reactions of electrodes that occurred in Li2SO4 and KOH electrolytes that restrict the CVWs are discussed. The results indicate that in the case of Li2SO4, the AC electrode can deliver a specific capacitance of 210 F g−1 at a current density of 0.1 A g−1, and the energy density of capacitor can be as high as 16.9 Wh kg−1 at 200 W kg−1 (based on the total mass of active electrode materials), 80% higher than that in the case of KOH.
Kinetics of Double-Layer Charging/Discharging of Activated Carbon Electrodes: Role of Surface Acidic Functional Groups
This work involves the role of surface acidic functional groups (SAFG) in the kinetics of double-layer charging/discharging of activated carbon powder electrode specimens in a 30 wt % H 2 SO 4 solution using nitrogen gas adsorption, the Boehm method, ac impedance spectroscopy, a potentiostatic current transient technique, and cyclic voltammetry, For this study, two kinds of as-activated and as-reactivated carbon powder specimens with nonuniformly distributed pore size were prepared, which were characterized by roughly the same pore size distribution, hut by appreciably different concentrations of the SAFG. The resistive and capacitive elements were roughly estimated using complex nonlinear least-squares fitting of the ac impedance spectra to a six-RC-element ladder network. The cathodic current transients and cyclic voltammograms (CVs) were simulated from the circuit analysis based upon the ladder network at a potential step and a potential scan, respectively, during double-layer charging/ discharging using six sets of calculated time constants. Both the simulated current transients and the CVs agreed well in shape and value with those experimentally measured. From the results, we conclude that the SAFG increase the time constant and decrease the rate capability, thus causing considerable retardation of ion penetration into the pores during double-layer charging/discharging of the carbon electrodes.