Electrical Double-layer Performance Research Articles

Electrochemical and Electric Field Response Properties of Highly Sensitive Electrodes Based on Carbon Fiber With Oxygen and Nitrogen Surface Groups

In this paper, a high-sensitive carbon fiber electrode enriched oxygen and nitrogen groups were prepared using a method combining oxidation and graft modification. The surface compositions were analyzed by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The electrochemical results show that the modified carbon fibers have a better electric double layer performance and a lower capacitive impedance at the lower frequency. The offset potential of the electrode pairs is typically below 1 mV with a drift of less than $40~\mu \text{V}$ /day. Typical measured noise level is below 2 nV/rt (Hz) at 1 Hz. The modified carbon fiber electrode pairs exhibit a good response to the ac sine signal of amplitude 1 mV and frequency 1 mHz. The sensitivity is increased by 82% and 59%, respectively, in comparison with Ag/AgCl electrode pair. The possible mechanism of the electric field response is discussed by the model of the electric double layer. This carbon fiber electrodes could provide the potential candidate and the theoretical basis for the design of high-sensitivity marine electric field sensor.

Three-Dimensional Hierarchical Porous Carbon with High Oxygen Content Derived from Organic Waste Liquid with Superior Electric Double Layer Performance

The organic waste liquid produced in the production of vitamin C is an acidic pollutant which is difficult for effective treatment and utilization, and lignin is an abundant biopolymer with abundan...

Coprecipitation Reaction System Synthesis and Lithium-Ion Capacitor Energy Storage Application of the Porous Structural Bimetallic Sulfide CoMoS4 Nanoparticles.

Lithium-ion capacitors (LICs) are noticed as a new-type of energy storage device with both capacitive mechanism and battery mechanism. The LICs own outstanding power density and energy density. In our work, an LIC was constructed by using a simple method to prepare a bimetallic sulfide of CoMoS4 nanoparticles as the anode and a self-made biochar [fructus cannabis’s shells (FCS)] with excellent specific surface area as the cathode. The CoMoS4//FCS LIC demonstrated that the range of energy density is from 10 to 41.9 W h/kg and the range of power density is from 75 to 3000 W/kg in the meantime, and it also demonstrated a remarkable cycling performance with the capacitance retention of 95% after 10 000 cycles of charging–discharging at 1 A/g. The designed CoMoS4//FCS LIC device exhibits a superior electrochemical performance because of the CoMoS4 loose porous structure leading to excellent dynamic performance, which is conducive to the diffusion of electrolyte and lithium ion transport, and good electric double layer performance of biochar with large specific surface area could be achieved. Therefore, this bimetallic sulfide is a promising active material for LICs, which could be applied to electric vehicles in the future.

Preparation of graphene nanowalls on nickel foam as supercapacitor electrodes

Graphene nanowalls (GNWs) were deposited on the surface of the copper foil, nickel foam and glass using the plasma-enhanced chemical vapour deposition (13.56 MHz) method. The etching effect of hydrogen on the morphology of the GNWs was investigated by varying the CH 4 /H 2 ratio during the graphene growth. Supercapacitor electrodes made of GNWs on nickel foam were tested with cyclic voltammetry and galvanostatic charge/discharge methods, showing premium electrical double-layer performance and cyclic stability.

Preparation and electrochemical capacitive performance of phenolated calcium lignosulfonate-based phenol formaldehyde resin porous carbon

Abstract

Microporous activated carbons from coconut shells produced by self-activation using the pyrolysis gases produced from them, that have an excellent electric double layer performance

Microporous activated carbons from coconut shells produced by self-activation using the pyrolysis gases produced from them, that have an excellent electric double layer performance

Microporous activated carbons from coconut shells produced by self-activation using the pyrolysis gases produced from them, that have an excellent electric double layer performance

Coconut shell-based activated carbons were prepared by self-activation using the pyrolysis gases generated from them. The process was carried out at high temperatures in a closed reactor filled with coconut shell under a high pressure that was generated by pyrolysis gases. Results indicate that the activated carbon prepared at 900 °C for 6h has a specific surface area, total pore volume, micropore percentage, iodine adsorption capacity and methylene blue adsorption capacity of 1 194.4 m2/g, 0.528 cm3/g, 87.8%, 1 280 mg/g and 315 mg/g, respectively. When used as the electrode material of electrochemical capacitors this activated carbon exhibits a specific capacitance of 258 F/g, a high capacitance retention rate of 97.2% after 3000 charge/discharge cycles and a small impedance. The water vapor and carbon dioxide generated by the pyrolysis of the coconut shell in the closed reactor act as activating agents and also increase the pressure of the reaction system. This is favorable for the activation of the formed char. This self-activation method was also used to prepare activated carbons with high adsorption capacities for iodine and methylene blue from almond stones, pecan shells and slash pine sawdust, indicating that it is a very simple, efficient, environmentally friendly and economical method for the preparation of biomass-based activated carbons for supercapacitor electrode materials and adsorption.

An Ideal Electrode Material, 3D Surface-Microporous Graphene for Supercapacitors with Ultrahigh Areal Capacitance.

The efficient charge accumulation of an ideal supercapacitor electrode requires abundant micropores and its fast electrolyte-ions transport prefers meso/macropores. However, current electrode materials cannot meet both requirements, resulting in poor performance. Herein, we creatively constructed three-dimensional cabbage-coral-like graphene as an ideal electrode material, in which meso/macro channels are formed by graphene walls and rich micropores are incorporated in the surface layer of the graphene walls. The unique 3D graphene material can achieve a high gravimetric capacitance of 200 F/g with aqueous electrolyte, 3 times larger than that of commercially used activated carbon (70.8 F/g). Furthermore, it can reach an ultrahigh areal capacitance of 1.28 F/cm2 and excellent rate capability (83.5% from 0.5 to 10 A/g) as well as high cycling stability (86.2% retention after 5000 cycles). The excellent electric double-layer performance of the 3D graphene electrode can be attributed to the fast electrolyte ion transport in the meso/macro channels and the rapid and reversible charge adsorption with negligible transport distance in the surface micropores.

Influence of the iodide/iodine redox system on the self-discharge of AC/AC electrochemical capacitors in salt aqueous electrolyte

Self-discharge (SD) of AC/AC (AC=activated carbon) electrochemical capacitors in aqueous solutions of lithium sulfate (Li2SO4) and lithium sulfate+iodide salts (Li2SO4+KI or Li2SO4+LiI) was investigated at 24°C and −40°C after cell potential hold at values from 1V to 1.6V. At 24°C, the cells exhibit lower SD in Li2SO4+KI than in Li2SO4, owing to the redox activity of the 2I−/I2 system which drives the positive AC electrode to operate in narrow potential range and display lower potential drop than in Li2SO4. At −40°C, the capacitors exhibit comparable and reduced SD both in Li2SO4+LiI and Li2SO4, whatever the holding cell potential. Three-electrode cell experiments demonstrate that, at −40°C, hydrogen chemisorption is thermodynamically unfavored under negative polarization, while the activity of the 2I−/I2 redox system under positive polarization is only slightly reduced. As a consequence, the AC/AC cells in Li2SO4 exhibit a typical electrical double-layer performance at −40°C, whereas they still behave as hybrid ones in Li2SO4+LiI, with twice higher capacitance than in Li2SO4. The (Ui-Ut) vs t1/2 plots demonstrate that SD is essentially controlled by diffusion at −40°C, suggesting that it originates from bulkier hydrated ions. Overall, in the investigated temperature range, the AC/AC capacitors in Li2SO4+LiI demonstrate low self-discharge and high capacitance, while being able to operate up to 1.6V.

Enhanced specific capacitance of modified needle cokes by controlling oxidation treatment

The electric double-layer performance of needle cokes can be affected by the morphology of structures. Hence, we introduce modified needle cokes by using simple oxidation treatment. The degree of graphitization with high specific capacitance is controlled by acid and heat treatment. The active sites of cokes are increased with increasing oxidation time. Dilute nitric acid (HNO3) and sodium chlorate (NaClO3) are used for the activation of cokes. In this case, the interlayer distance is dramatically increased from 3.5 to 8.9 Å. The specific capacitances are 33 F g−1 and 30 F ml−1, respectively, on a two-electrode system with a potential range of 0–2.5 V. The behaviors of double-layer capacitance are demonstrated by the charge–discharge process and the morphologies of modified needle cokes are analyzed by XRD, FE-SEM, BET and elemental analysis.

The role of mass transport pathway in wormholelike mesoporous carbon for supercapacitors

In the present paper, we demonstrate the importance of the role of a mass transport pathway (MTP) in wormholelike mesoporous carbon (WMC) through studying the ion diffusion behaviors within two different wormholelike mesopore networks with and without MTP. Our results reveal that the introduction of MTP is very helpful in improving ion diffusion properties. The as-prepared WMC with a MTP of ca. 9.7 nm exhibits notably better electric double layer performance as compared to the conventional WMC without a MTP. For example, even at the quick sweep rate of 50 mV s(-1), the surface specific capacitance of the former is 21.6 microF cm(-2), which is almost 4 times as high as that of the latter (5.5 microF cm(-2)).

Preparation and Electrochemical Performance of Novel Ordered Mesoporous Carbon with an Interconnected Channel Structure

A novel ordered mesoporous carbon with an interconnected channel structure (OMC-IC) has been successfully fabricated by adding proper hydrophilic SiO(2) nanoparticles to the solution of triblock copolymer F127 and phenol-formaldehyde resol. Experimental results show that the presence of SiO(2) nanoparticles does not hamper the self-assembly of F127 and resol to form an ordered two-dimensional hexagonal mesostructure. The neighboring channels of the OMC-IC are interconnected after removing SiO(2) nanoparticles with a diameter larger than the thickness of the carbon wall. Such an interconnectivity of channels is beneficial in improving ion diffusion properties. The as-prepared OMC-IC exhibits much lower impedance to ion transport within both the channels and the micropores in the carbon wall, and thus has better electric double layer performance as compared to the conventional OMC with an unconnected channel structure.

Preparation and Electrochemical Performance of Polyimide Derived Activated Carbon

Polyimide derived activated carbon was prepared by carbonization and KOH activation, which was used for electrode material of electric double-layer capacitors.Its pore structure and surface chemical property were studied by DFT and XPS,respectively,and its electrochemical properties were studied by electrochemical methods,such as,charge-discharge of constant current.The results show that both the nitrogen content and the porosity of sample CPI affect its gravimetric capacitance.After activation,the specific areas of sample API reach 1941m~2/g,the micropore formed is all less than 2nm.The effect of nitrogen atom can be ignored.Its gravimetric capacitance reach 300F/g with the discharging current density of 50mA/g,and remain 86.1% of its capacitance when the current density reaches 1000mA/g.The results of impedance also show that sample API has good electric double-layer performance which is novel electrode material for electric double layer capacitor.

Characterization of 1‐D nanoSiC‐derived nanoporous carbon

AbstractThe basic interest of this study was to see whether and how the sorption and electrical double layer (EDL) properties of porous whiskers‐like carbide‐derived carbon (CDC) from SiC nanofibres differ from the commercial SiC‐derived carbon. SiC nanofibres were obtained via combustion synthesis route from CaSi2/PTFE mixture. Resulting carbon material was analysed by powder XRD and low‐temperature nitrogen sorption methods. EDL characteristics were evaluated and compared with CDC obtained from α‐SiC and β‐SiC powders. The cyclic voltammograms and the electrochemical impedance spectroscopy show that the electrical double layer performance of SiC nanofibres‐derived amorphous carbon is better than most of the common pyrolytically made carbons. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)