Nanoporous Carbon Electrodes Research Articles

Fabrication and textural characterization of nanoporous carbon electrodes embedded with CuO nanoparticles for supercapacitors

We introduce a novel strategy of fabricating nanoporous carbons loaded with different amounts of CuO nanoparticles via a hard templating approach, using copper-containing mesoporous silica as the template and sucrose as the carbon source. The nature and dispersion of the CuO nanoparticles on the surface of the nanoporous carbons were investigated by x-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and high-resolution transmission electron microscopy (HRTEM). XRD results reveal that nanoporous carbons with embedded CuO nanoparticles exhibit a well-ordered mesoporous structure, whereas the nitrogen adsorption measurements indicate the presence of excellent textural characteristics such as high surface area, large pore volume and uniform pore size distribution. The amount of CuO nanoparticles in the nanochannels of the nanoporous carbon could be controlled by simply varying the Si/Cu molar ratio of the mesoporous silica template. Morphological characterization by SEM and TEM reveals that high-quality CuO nanoparticles are distributed homogeneously within the nanoporous carbon framework. The supercapacitance behavior of the CuO-loaded nanoporous carbons was investigated. The material with a small amount of CuO in the mesochannels and high surface area affords a maximum specific capacitance of 300 F g-1 at a 20 mV s-1 scan rate in an aqueous electrolyte solution. A supercapacitor containing the CuO-loaded nanoporous carbon is highly stable and exhibits a long cycle life with 91% specific capacitance retained after 1000 cycles.

Sensitive determination of dihydronicotinamide adenine dinucleotide and ethanol with a nano-porous carbon electrode

A nano-porous carbon electrode, fabricated in 0.1 mol L?1 NaOH by the electrochemical technique, was used for the electrochemical detection of dihydronicotinamide adenine dinucleotide, NADH, with an overpotential decrease of about 270 mV and a linear range from 1.0 ? 10?6 to 1.0 ? 10?4 mol L?1. Amperometric sensing of ethanol cooperating with alcohol dehydrogenase and nicotinamide adenine dinucleotide was successfully demonstrated. A linear response in the range from 5.0 ? 10?5 mol L?1 to 1.0 ? 10?2 mol L?1 was obtained, with a detection limit of 1.0 ? 10?5 mol L?1. The method was successfully employed to determine ethanol in beer with high precision.

A prototype cell for extracting energy from a water salinity difference by means of double layer expansion in nanoporous carbon electrodes

Electrical energy can be obtained from the controlled mixing of fresh (river) and saline (sea) water. Existing technologies such as pressure retarded osmosis and reverse electrodialysis make use of ion-exchange membranes which must be crossed by either the water or the ions. Recently a new physical principle has been experimentally demonstrated, which allows extraction of electrical energy without making use of membranes, based on the temporary storage of ions inside two porous electrodes kept at different electrical potentials, and the repeatable expansion/contraction of the electrostatic double layers formed inside the electrodes upon changing the salt concentration [D. Brogioli, Phys. Rev. Lett., 2009, 103, 058501]. To make further investigations and to improve the energy recovery, we developed a simple prototype cell of much larger dimensions. Because of the larger dimensions (thus higher currents), testing is more facile, while this design can be the basis for further scaling-up of this technology. In order to reduce the internal resistance of the cell, the electrodes are no longer placed side-by-side, but parallel to one another, separated only by a 250 μm-thick open spacer channel to form a “sandwich”-like flow cell. In a lab-scale experimental stack consisting of 8 such cells (with outer dimensions 6 × 6 × 1 cm3) we extract about 2 J per charging/discharging cycle in 500 mM/1 mM NaCl salt solution, an amount which is 20 times higher per cycle per unit electrode mass than previously obtained. The extracted energy increases with the operating voltage, in line with predictions of the Gouy-Chapman-Stern model for double layer formation.

Electrochemical Characteristics of Bi(111) and Nanoporous Carbon Electrodes in Ionic Liquids

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A new type of high energy asymmetric capacitor with nanoporous carbon electrodes in aqueous electrolyte

A new type of low cost and high energy asymmetric capacitor based on only activated carbons for both electrodes has been developed in a safe and environment friendly aqueous electrolyte. In such electrolyte, the charges are stored in the electrical double-layer and through fast faradaic charge transfer processes. By taking profit of different redox reactions occurring in the positive and negative ranges of potential, it is possible to optimize the capacitor either by balancing the mass of the electrodes or by using different optimized carbons for the positive and negative electrodes. The best results are obtained in the latter case, by utilizing different pseudo-faradaic properties of carbons in order to increase the capacitance and to shift the potentials of water decomposition and destructive oxidation of activated carbon to more negative and positive values, respectively. After an additional adjustment of potentials by mass-balancing the two electrodes, the electrochemical capacitor can be reversibly charged/discharged at 1.6 V in aqueous medium, with energy densities close to the values obtained with electrical double-layer capacitors working in organic electrolytes, while avoiding their disadvantages.

The Rate-Determining Step of Electroadsorption Processes into Nanoporous Carbon Electrodes Related to Water Desalination

Using potential perturbation techniques, we investigated the kinetics of electroadsorption processes of ions with different dimensions and different concentrations into activated carbon electrodes with various porous structures. We found that the ratio between the pore size and the ion size is of great significance in terms of electroadsorption kinetics. Microporous carbon fiber electrodes exhibited a lower charging rate as compared with mesoporous aerogel carbon. The use of activated aerogel electrodes with a fractal structure composed of both micro- and mesopores, was found to be the best for effective electroadsorption due to both high electrical double layer capacity obtained and high rates of electroadsorption. We also explored the kinetics of electroadsorption processes into molecular sieve carbon electrodes, demonstrating that, despite the hindered adsorption processes into these electrodes, it is possible to obtain effective deionization by using them for selective water desalination processes.

Influence of Mesoporous Separator Properties on the Parameters of Electrical Double-Layer Capacitor Single Cells

The specific surface area, pore size distribution function, micropore and mesopore volume, and area values have been obtained by gas adsorption/absorption method for various separator materials prepared from polypropylene, cellulose, and poly(vinylidene fluoride). Electrical double-layer capacitors (EDLCs) based on the two identical ideally polarizable nanoporous carbide-derived carbon electrodes and different mesoporous separator materials in acetonitrile solution have been tested by cyclic voltammetry and electrochemical impedance methods. The limits of ideal polarizability, low-frequency limiting capacitance and series resistance, time constant, complex power components, and electrolyte conductivity in the separator matrix have been obtained and discussed. The model of Srinivasan and Weidner [ J. Electrochem. Soc. , 146 , 1650 (1999)] has been modified by introducing into it the very high-frequency constant phase and charge-transfer resistance elements. The applicability limits of the modified model have been tested. Noticeable influence of separator chemical composition, thickness, specific surface area, and pore size distribution on the characteristics of the EDLC single cells have been found.

Micro- and Mesoporous Carbide-Derived Carbon Materials and Polymer Membranes for Supercapacitors

Several nanoscale fine-tuned micro- and mesoporous carbon powders C(Mo2C) produced by reacting Mo2C with Cl2 at various temperatures were studied and characterized using XRD and Raman spectroscopy methods and compared with low temperature N2 adsorption/desorption measurements data. Supercapacitors based on two ideally polarizable nanoporous carbon electrodes and different mesoporous commercially available separators in acetonitrile (AN) as the solvent for the 1.0 M (C2H5)3CH3NBF4 electrolyte have been completed and tested by cyclic voltammetry and electrochemical impedance methods.

Nanoporous carbon electrode from waste coffee beans for high performance supercapacitors

Activated carbon was produced from waste coffee grounds by treatment with ZnCl 2. Supercapacitor electrodes prepared from this coffee grounds carbon exhibited energy densities up to 20 Wh kg −1 in 1 M H 2SO 4, and excellent stability at high charge–discharge rates. In a two-electrode cell a specific capacitance as high as 368 F g −1 was observed, with rectangular cyclic voltammetry curves and stable performance over 10,000 cycles at a cell potential of 1.2 V and current load of 5 A g −1. The good electrochemical performance of the coffee grounds carbon was attributed to a well developed porosity, with a distribution of micropores and mesopores 2–4 nm wide, and the presence of electrochemically active quinone oxygen groups and nitrogen functional groups. This work highlights the potential to utilize waste biomass to produce electrode materials for cost-effective energy storage systems.

Electrochemical properties of colchicine on the PoPD/SWNTs composite-modified glassy carbon electrode

Abstract A poly(o-phenylenediamine)/single-wall carbon nanotubes-modified electrode was prepared by electropolymerization on glassy carbon electrode. The morphology of the resulting PoPD/SWNTs composite was characterized by transmission electron microscopy (TEM) and the electrochemical properties of the modified electrode were characterized by cyclic voltammetry and ac impedance. The nanoporous composite film-modified glassy carbon electrode exhibits enhanced electrocatalytic behavior and good stability for the detection of colchicine. The large current response of colchicine on PoPD/SWNTs composite-modified electrode is probably caused by the synergistic effect of the electrocatalytic property of PoPD and SWNTs. The oxidative peak current increased linearly with the concentration of colchicine in the range of 1.0 × 10−7 to 1.0 × 10−5 mol l−1 by differential pulse voltammetry. The detection limit was 3.5 × 10−8 mol l−1. The proposed modified electrode provides a new promising and alternative way to detect colchicine.

Micro- and Mesoporous Carbon Based Electrode Materials for Electrical Double Layer Capacitors

Micro- and mesoporous carbons are attractive electrode materials with the unique porous structure, narrow pore size distribution and possibility to fine-tune the pore size for electrodes of electrical double layer capacitors (EDLC), commonly called supercapacitors. The excellent adsorptivity of carbide-derived carbon (CDC) has been demonstrated but these materials are quite expensive and the main aim of this work was to establish conditions for the preparation of nanoporous carbon electrodes, based on less expensive raw materials, synthesis and activation (i.e. with H2O vapor) methods.

Thermal-to-electric energy conversion of a nanoporous carbon

As two nanoporous carbon electrodes are soaked by an electrolyte solution and placed at different temperatures, a significant transient potential was measured, providing a novel mechanism for thermal-to-electric energy conversion.

Characterisation of activated nanoporous carbon for supercapacitor electrode materials

Commercial nanoporous carbon RP-20 was activated with water vapor in the temperature range from 950 °C to 1150 °C. The XRD analysis was carried out on nanoporous carbon powder samples to investigate the structural changes (graphitisation) in modified carbon that occurred at activation temperatures T ⩾ 1150 °C. The first-order Raman spectra showed the absorption peak at 1582 cm −1 and the disorder (D) peak at 1350 cm −1. The low-temperature N 2 adsorption experiments were performed at −196 °C and a specific surface area up to 2240 m 2g −1 for carbon activated at T = 1050 °C was measured. The cell capacitance for two electrode activated nanoporous carbon system advanced up to 60 F g −1 giving the specific capacitance ∼240 F g −1 to one electrode nanoporous carbon ∣1.2 M (C 2H 5) 3CH 3NBF 4 + acetonitrile solution interface. A very wide region of ideal polarisability for two electrode system (∼3.2 V) was achieved. The low frequency limiting specific capacitance very weakly increases with the rise of specific area explained by the mass transfer limitations in the nanoporous carbon electrodes. The electrochemical characteristics obtained show that some of these materials under discussion can be used for compilation of high energy density and power density non-aqueous electrolyte supercapacitors with higher power densities than aqueous supercapacitors.

Use of organic esters as co-solvents for electrical double layer capacitors with low temperature performance

The electrochemical characteristics of the electrical double layer capacitor (EDLC) single cell based on the nanoporous carbon electrode in 1 M (C2H5)3CH3NBF4 (TEMA) solution in various non-aqueous organic carbonate and organic ester binary, ternary and quaternary solvent systems (ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl formate (MF), methyl acetate (MA) and ethyl acetate (EA)) mixed in the x:y, x:y:z and x:y:z:f volume ratios, respectively) have been studied using the cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) methods. The specific capacitance, phase angle, series and parallel resistance values dependent on the solvent system used have been calculated. The region of ideal polarisability of nanoporous carbon electrodes ΔE ⩾ 3.0 V for 1 M TEMA in various binary, ternary and quaternary non-aqueous solvent systems has been achieved. Specific conductivity values for 1 M TEMA solution in various organic carbonate – organic ester based electrolytes have been obtained at −40 °C < T < 50 °C and compared with electrochemistry data.

Matching the nanoporous carbon electrodes and organic electrolytes in double layer capacitors

In order to see how the power density of supercapacitors could be increased, a theoretical model of the nanoporous carbon electrode as a tier structure with transport channels has been developed. Also an experimental method has been developed to measure the rate of electrolyte transport through the porous electrode material. This method can be used for quick analysis and selection of electrodes. The results of modeling have been verified by testing the experimental EDLC prototypes with optimum electrode thickness and electrode porosity, the porosity being well matched with the size of ions in organic electrolytes. This enables us to reach a power density as high as 6–7 kW/L with a reasonably large energy density and high efficiency for both EDLC unit cells and stacks.

Electrochemical Behavior of Stimulation∕Sensing Materials for Pacemaker Electrode Applications: III. Nanoporous and Smooth Carbon Electrodes

The electrochemical behavior of nanoporous and smooth carbon electrodes was investigated in a phosphate-buffered saline solution. The interfacial properties were characterized by electrochemical impedance spectroscopy. The influence of charging∕discharging rate on the capacitive behavior was investigated by cyclic voltammetry between and at fast sweep rates. The transient processes taking place at the electrode upon stimulation pulse were also studied by using a pulse generator. For the nanoporous electrode at sufficiently high sweep rates, the charge-transfer characteristics change from capacitive to resistive, due to voltage drop down the pores. Only a small part of total available capacitance of the porous electrode can be utilized at high charging∕discharging rates. This is probably the reason for the observed relationship between pacing impedance and geometric electrode surface area. When subjected to stimulation pulses, compared to the smooth electrode, the nanoporous electrode delivers more charge due to lower pacing impedance. At high pulse potentials, some faradaic reaction seems to occur, which is more pronounced on the smooth electrode.

Organic carbonate–Organic ester-based non-aqueous electrolytes for electrical double layer capacitors

The electrical characteristics of the electrical double layer capacitors based on the nanoporous carbon|1 M triethylmethylammonium tetrafluoroborate in ethylene carbonate mixed with dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl formate, methyl acetate and ethyl acetate in the 1:1 volume ratio have been studied using the cyclic voltammetry and the electrochemical impedance spectroscopy methods. The specific series and parallel capacitances, phase angle, time constant, series and parallel resistances dependent on the binary solvent system used have been established. The region of ideal polarisability of nanoporous carbon electrodes Δ E ⩾ 3.0 V for 1 M (C 2H 5) 3CH 3NBF 4 in various binary non-aqueous solvent systems has been achieved. Specific conductivity values for 1 M TEMA solution in various organic carbonate-based electrolytes have been obtained at −40 °C < T < 50 °C and compared with the electrochemical data.

Investigation of Pt, Ti, TiN, and nano-porous carbon electrodes for implantable cardioverter-defibrillator applications

The electrochemical behavior and stability of Pt, Ti, TiN, and nano-porous carbon for implantable cardioverter-defibrillator (ICD) electrode application were investigated in a phosphate buffered saline solution. The electrochemical interfacial properties were examined by electrochemical impedance spectroscopy, and the potential and current response during ICD shock pulses were recorded by a digital oscilloscope. Changes in surface composition and structure were investigated using X-ray photoelectron spectroscopy and environmental scanning electron microscopy. When exposed to anodic 700 V shock pulses with duration of 10 ms, only Pt was stable, nano-porous carbon electrode was slightly attacked, whereas Ti and TiN electrodes suffered severe degradation. Upon cathodic shock pulsing, all the materials were stable, but Ti and TiN electrodes with a smooth surface showed evidence of hydrogen adsorption. Porous and rough electrodes produced less gas evolution compared to a smooth surfaces, due to a higher amount of charge transferred through non-Faradaic processes. The reason for this could be higher interfacial capacity due to the large surface area.

Voltammetric and electrochemical impedance spectroscopy studies of the nanoporous carbon|1 M (C 2H 5) 3CH 3NBF 4 electrolyte solution interface

The electrical double-layer and electrochemical characteristics at the nanoporous carbon|acetone, acetonitrile, γ-butyrolactone and propylene carbonate interfaces with addition of (C 2H 5) 3CH 3NBF 4 electrolyte have been studied by cyclic voltammetry and electrochemical impedance spectroscopy methods. The region of ideal polarizability, values of series and parallel capacitances, pore resistance and other characteristics have been established. Analysis of complex impedance plane plots shows that the nanoporous carbon|1 M (C 2H 5) 3CH 3NBF 4 electrolyte interface can be simulated by an equivalent circuit, in which the two parallel conduction parts in the solid and liquid phases are interconnected by the double-layer capacitance in parallel with the complex admittance of hindered reaction of the charge transfer process or of the partial charge transfer (i.e., adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte composition (i.e., on the solvent viscosity and dielectric constant) and on the electrode potential (i.e., on the Gibbs adsorption energy of the solvent molecules and ions at the surface of the nanoporous carbon electrode dependent on the electrode potential). The modified combined Frumkin–Melik-Gaikazyan and Randles-like equivalent circuit, combined Voigt and Frumkin–Melik-Gaikazyan and Newman et al. models have been used for the simulation of the complex impedance plane plots.

Influence of solvent nature on the electrochemical characteristics of nanoporous carbon|1 M (C 2H 5) 3CH 3NBF 4 electrolyte solution interface

Electrochemical characteristics of the nanoporous carbon|acetonitrile (AN), γ-butyrolactone (γ-BL) and propylene carbonate (PC) interface with addition of (C 2H 5) 3CH 3NBF 4 electrolyte have been studied by cyclic voltammetry and electrochemical impedance spectroscopy. The region of ideal polarisability, values of series and parallel capacitance, pore resistance and other characteristics dependent on the viscosity of solvents and molar conductivity of electrolyte have been established. Analysis of complex plane plots shows that the nanoporous carbon|1 M (C 2H 5) 3CH 3NBF 4 electrolyte interface can be simulated by an equivalent circuit, in which the two parallel conduction parts in the solid and liquid phases are interconnected by the double layer capacitance in parallel with the complex admittance of hindered reaction of the charge transfer process or of the partial charge transfer process. The values of the characteristic frequency depend on the electrolyte composition and on the electrode potential, i.e., on the viscosity and dipole moment of ions adsorbed at the surface of nanoporous carbon electrode.