Papers by Keyword: Electric Double-Layer Capacitor

Abstract: TiO₂ nanotube arrays (TiO₂ NTAs) were prepared by anodization method. The as-prepared TiO₂ NTAs were annealed at 450 °C for 3 h transforming amorphous TiO₂ to anatase TiO₂. The inner diameter and tube length of synthesized TiO₂ NTAs are approximately 100 nm and 1.0 mm, respectively. Electric double-layer capacitor (EDLC) was fabricated using TiO₂ NTAs as electrodes with 6 M KOH electrolyte. The internal resistance of the EDLC is relatively low (3.8 – 6.5 Ω) depending on the operating temperature. This work confirmed experimentally the use of TiO₂ NTAs as EDLC electrodes.

Abstract: High surface area activated carbon (AC) obtained by KOH activation of petroleum coke was leached by HCl aqueous solution and the effects of the ash contents of AC on performance of electric double layer capacitors (ECs) in 3M KOH aqueous electrolyte and 1 M (C2H5)4NBF4/propylene carbonate electrolyte were investigated by cyclic chronopotentiograms and electrochemical impedance spectrometry (EIS). An equivalent circuit model based on a mixed kinetic and charge transfer control was proposed to fit EIS spectra. The model parameters were extracted by Marquardt best fitting. The series solution resistances, polarization resistance and diffusion coefficient related to Warburg impedances were obtained. It is found that the series solution resistances remained constant, polarization resistances decreased and the diffusion coefficients increased after acid leaching for each electrolyte, indicating that acid leaching can remove the electronic inert ash, which decreases contact resistance among particles of activated carbon and opens or widens the blocked pores by ash components. Moreover, the specific capacitances of AC were increased by the acid leaching.

Abstract: We reported the preparation and electrochemical properties of fluorinated mesoporous carbon foams (F-MCFs) for application as electric double-layer capacitors (EDLCs). By using fluorinated resol which was obtained from the polymerization of formaldehyde, phenol, and 3-fluorophenol as the carbon source and fluorin precursor, and triblock copolymer F127 as a template, F-MCFs were prepared through evaporation induced self-assembly strategy. The F-MCFs were characterized by N₂ adsorption and desorption, transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The results indicate that the F-MCFs possess highly ordered mesostructure with a specific surface area of 675 m²/g, a uniform pore size of 2.2 nm and a pore volume of 0.12 cm³/g. The wettability of F-MCFs was investigated by contact angle analysis. The contact angle of F-MCFs for water is 111.5^o, much lower than that of mesoporous carbon foams (MCFs) (141^o), indicating that the surface wettability of F-MCFs is improved by the introduction of fluorin into the carbon matrix. The enhancement of wettability would increase the surface contact of electrolyte and electrode and accelerate the ion transfer within the pore channel, and thus improve the electrochemical properties of F-MCFs. The electrochemical properties of the F-MCFs have been investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge in electrolyte of 6 mol/L KOH with a three-electrode system. F-MCFs present linear galvanostatic charge-discharge curve at a loading current of 10 mA, and possess good charge-discharge efficiency over 98%. The specific capacitance of the F-MCFs is 220 F/g, significantly higher than that of the MCFs (140 F/g). F-MCFs show important prospect as electrode materials for the application in EDLCs.

Abstract: Direct preparation of activated carbon (AC) from coal was reported by microwave heating with potassium hydroxide as activation agent. Electrochemical properties of AC electrodes were investigated by cyclic voltammetry, constant current charge–discharge. The results show that functional groups on AC include –C=O, –O–H and –C–O. The micropore volume of AC from different coal totals 48.5–95.6%. The total pore volume of AC from different coal passes through a maximum with the decrease of volatile mater content in coal. The specific surface area and total pore volume of AC from Qing ting coal reach 1874 m² g^-1 and 1.00 cm³ g^-1, respectively. The specific capacitance and energy density of AC from higher coal rank is usually bigger than that of AC from lower coal rank.

Abstract: Bamboo-shaped carbon nanotubes (BCNTs) have been synthesized by chemical vapor deposition method. The activated BCNTs after simple ball milling and KOH etching are used as polarizable electrodes in electric double layer capacitor (EDLC). Our results show that the specific capacity of BCNTs can be improved by the activation treatment.

Abstract: When fine-sized 45ZnO·55P2O5 or 50ZnO·50P2O5 glass powders were mixed with distilled water, hydration immediately occurred, resulting in the formation of viscous hydrogels. 31P MAS-NMR spectra showed that the hydrogels contain orthophosphates and long-chain phosphates; no significant differences in their structures between the hydrogels were shown. The 45ZP gel and 50ZP gel showed high conductivities (e.g., 9.9 and 2.8 mS/cm, respectively, at 30°C). The conductivities were related to the proton amount in the hydrogel; the amount in the 45ZP gel was larger than that in the 50ZP gel. Electric double-layer capacitors (EDCs) were prepared using electrolytes consisting of the hydrogels. The specific capacities of the EDC cell for the 45ZP gel and 50ZP gel were 2.40 and 2.06 F/g, respectively. The possibility as an EDC electrolyte may be related to proton conductivities of the hydrogels.