Double-layer Electrode Research Articles

Assessment of Liquid Crystal Template Deposited Porous Nickel as a Supercapacitor Electrode Material

The high surface area porous nickel, obtained by template electrodeposition using a hexagonal liquid crystalline phase medium as a template was evaluated as a potential material for electrochemical capacitors using cyclic voltammetry ~CV! and electrochemical impedance spectroscopy ~EIS! studies in 6 M KOH. A single electrode double layer capacitance of 1.4 F/cm2 ~at 2 mV/s scan rate! was obtained using CV, which corresponds to a specific capacitance of 473 F/g. EIS studies show the typical behavior of a porous electrode and the data were analyzed in terms of complex capacitance and complex power from which the relaxation time constant stod has been determined. Nickel oxide electrode, obtained by the electrochemical oxidation of porous Ni, shows a double layer capacitance value of 171 mF/cm2, which corresponds to a specific capacitance of 57 F/g. The relaxation time constants for the template deposited porous nickel and nickel oxide were determined to be 1.35 s and 33 ms, respectively. The values of double layer capacitance and specific capacitance of the porous nickel with fast response time are the highest values reported for nickel in the literature so far. © 2005 The Electrochemical Society. @DOI: 10.1149/1.1911931# All rights reserved.

Investigation of Ig.G Adsorption and the Effect on Electrochemical Responses at Titanium Dioxide Electrode

The adsorption of Immunoglobulin G on a titanium dioxide (TiO(2)) electrode surface was investigated using (125)I radiolabeling and electrochemical impedance spectroscopy (EIS). (125)I radiolabeling was used to determine the extent of protein adsorption, while EIS was used to ascertain the effect of the adsorbed protein layer on the electrode double layer capacitance and electron transfer between the TiO(2) electrode and the electrolyte. The adsorbed amounts of Ig.G agreed well with previous results and showed approximately monolayer coverage. The amount of adsorbed protein increased when a positive potential was applied to the electrode, while the application of a negative potential resulted in a decrease. Exposure to solutions of Ig.G resulted in a decrease of the double layer capacitance (C) and an increase in the charge-transfer resistance (R(2)) at the electrode solution interface. As more Ig.G adsorbed onto the electrode surface, the extent of C and R(2) variation increased. These capacitance and charge-transfer resistance variations were attributed to the formation of a proteinaceous layer on the electrode surface during exposure.

Scanning Electrochemical Microscopy, 52. Bipolar Conductance Technique at Ultramicroelectrodes for Resistance Measurements

The bipolar conductance, BICON, technique for the measurement of solution resistance, based on the application of microsecond current pulses, as originally described by Enke and co-workers for measurements with conventional electrodes, was extended for use with ultramicroelectrodes, with a focus on its application in scanning electrochemical microscopy (SECM). When the plateau time used to make the measurement lies within the BICON conditions, the solution conductance can be obtained directly from the output without the need for calibration curves. However, decreasing the size of the ultramicroelectrode decreases the range of values that satisfy these conditions, and one must resort to calibration curves to obtain solution conductance from the measured current, which was nevertheless found to be proportional to electrolyte concentration with electrodes as small as 5 mum in diameter. BICON/SECM approach curves over insulating substrates followed SECM negative feedback theory and approach curves in the presence of low (micromolar) or no added electrolyte are possible once the background conductivity is taken into account. Approach curves to a conducting substrate at open circuit potential are influenced by the solution time constant (solution resistance at the electrode tip x electrode double layer capacitance), which is a function of the tip/substrate distance, as well as the substrate size.

Copper electrodeposition from sulfate electrolytes in the presence of hydroxyethylated 2-butyne-1, 4-diol

Data has been obtained on the levelling effect of hydroxyethylated-2-butyne-1, 4-diol (“Ferasine”) in the copper electrodeposition from acidic sulfate electrolytes using cyclic voltammetry, hydrodynamic quasi steady-state voltammetry at rotating disc electrodes (RDE) and electrochemical impedance measurements. These are corroborated with morphological and structural analysis of copper deposits leading to the conclusion that finer grained deposits are produced, promoting a [110] texture. The additive moderately hinders the mass transfer of the copper ions from the bulk solution to the outer limit of the electrode double layer. Due to its adsorption on the electrode surface, Ferasine inhibits the charge transfer and slightly changes the copper electrodeposition mechanism. It affects the electrocrystallization step, impeding the crystal growth process and promoting the nucleation of copper.

A study of activated carbon nanotubes as double-layer capacitors electrode materials

Activated carbon nanotubes (CNTs) were produced by acid treatment. The activated CNTs and the initial CNTs were both used as the electric double-layer capacitors (EDLCs) electrode materials. The activated CNTs had much higher BET specific surface area, pore volume and lower volume ratio of micropores than those of the initial CNTs. Moreover, some kinds of functional groups were added on the surface of activated CNTs.The specific capacitance of the CNTs activated by mixture acid of H 2SO 4 and HNO 3 was above 2.5 times that of the initial CNTs. The activated CNTs and the initial CNTs were both examined by transmission electron microscopy (TEM) and infrared spectrum apparatus.

Transparent conducting metal electrode for top emission organic light-emitting devices: Ca–Ag double layer

We have fabricated a transparent conducting double-layer metal electrode for top emission organic light-emitting devices which consists of thin layers of Ca and Ag metals of different thicknesses, deposited by the vacuum evaporation technique. The process is clean and does not damage the underlaying organic layers. High optical transparency over 70%, low reflectivity (14%) in the visible region, and low electrical sheet resistance (12 ohms/square) in Ca(10 nm)–Ag(10 nm) structures are reported. This transparent conducting Ca–Ag metal electrode opens a practical way to fabricate top-emitting organic displays without generating damage-induced states.

Peculiarities and requirements of asymmetric capacitor devices based on combination of capacitor and battery-type electrodes

New concepts have arisen in recent years concerning configurations of the so-called hybrid charge-storage devices in which a faradaic, rechargeable battery-type electrode is combined with a non-faradaic, electrochemical, double-layer type of electrochemical capacitor electrode, the combination now being referred to as an “asymmetric” device. Other hybrid systems combine a double-layer electrochemical capacitor device with a fuel-cell or a separate rechargeable battery. Following a discussion of dependence of cell voltage of regular, two-electrode, non-faradaic electrochemical capacitors on state-of-charge (SOC), comparisons are made with recently conceived hybrid combinations of a battery-type rechargeable electrode with a double-layer capacitor-type electrode. Advantages, disadvantages and requirements of such hybrid systems over regular electrochemical supercapacitors or batteries are discussed and critically examined in regard to available energy- and power-densities, energy and coulombic efficiency, cycle-life, voltage profiles on discharge, and self-discharge behaviour. Emphasis is given to importance of using a third electrode, as reference, especially in evaluations of discharge/recharge behaviour of each electrode of an hybrid pair having very different electrochemical characteristics, one faradaic, the other non-faradaic. Use of a reference electrode also provides the opportunity of following self-discharge behaviour of the individual electrodes independently.

Preparation of high surface area nickel electrodeposit using a liquid crystal template technique

We show in this work that template electrodeposition of nickel at room temperature from a nickel sulphamate bath prepared in a new hexagonal liquid crystalline phase of water–Triton X-100–poly (acrylic acid) results in a highly porous surface. The roughness factor value of about 3620 obtained for this coating is the highest value reported in the literature for any electrodeposited nickel. The scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) pictures show the formation of porous deposit with granular features in between the pores. The single electrode double layer capacitance value measured for the deposit is 338 mF cm −2, which translates into a specific capacitance of 50 F g −1 without any post-thermal treatment of the electrode, suggesting its utility in super capacitors. Electrochemical studies using cyclic voltammetry (CV), Tafel plots and electrochemical impedance spectroscopy (EIS) and comparison of these results with some existing high surface area Ni catalysts show that the material has potential application as an excellent hydrogen evolving cathode.

P‐48: High Transparent Metal Electrode for Flexible Displays

AbstractIn this study, a high transparent electrode using metal for flexible displays, deposited by the vacuum thermal technique, is investigated. Double layer electrode, consisting of the calcium of 10nm and silver of 10nm, has a high transmittance over 75%, having in addition a low resistance below 12Ω/sq. This deposition process of Ca‐Ag thin metal electrode is without any permanent damage to underlying organic layers and strong against any mechanical deformation.

Peculiarities and requirements of asymmetric capacitor devices based on combination of capacitor and battery-type electrodes

New concepts have arisen in recent years concerning configurations of the so-called hybrid charge-storage devices in which a faradaic, rechargeable battery-type electrode is combined with a non-faradaic, electrochemical, double-layer type of electrochemical capacitor electrode, the combination now being referred to as an “asymmetric” device. Other hybrid systems combine a double-layer electrochemical capacitor device with a fuel-cell or a separate rechargeable battery. Following a discussion of dependence of cell voltage of regular, two-electrode, non-faradaic electrochemical capacitors on state-of-charge (SOC), comparisons are made with recently conceived hybrid combinations of a battery-type rechargeable electrode with a double-layer capacitor-type electrode. Advantages, disadvantages and requirements of such hybrid systems over regular electrochemical supercapacitors or batteries are discussed and critically examined in regard to available energy- and power-densities, energy and coulombic efficiency, cycle-life, voltage profiles on discharge, and self-discharge behaviour. Emphasis is given to importance of using a third electrode, as reference, especially in evaluations of discharge/recharge behaviour of each electrode of an hybrid pair having very different electrochemical characteristics, one faradaic, the other non-faradaic. Use of a reference electrode also provides the opportunity of following self-discharge behaviour of the individual electrodes independently.

Determination of the thicknesses of the active layer and cathode limiting currents in AFC

A series of double-layered gas diffusion electrodes with two different electrocatalysts, i.e., Ag and pyrolyzed macrocycle mixture (PMM) were prepared in order to find out the maximum limiting current densities ( i L) by varying the oxygen partial pressures in 6 M KOH and at 65 °C. As optimization of the active (catalyst) layer is important for better utilization of the catalytic reactions for oxygen reduction and thereby attainment of high current density, electrochemical measurements in half-cells were carried out to substantiate the current–thickness relationships. The thicknesses for both the active layers and diffusion layers were determined by using SEM. i L for an oxygen concentration simulating that of air was found to be 2.2 A cm −2 for the PMM with 0.51 mm and 1.6 A cm −2 for the Ag-based catalyst with 0.56 mm thicknesses of the active layer. An overlay of a mathematical model, describing the parameters for determination of i L, has also been inserted alongside the experimental values.

Effect of Temperature on Hydrogen Adsorption on Pt(111), Pt(110), and Pt(100) Electrodes in 0.1 M HClO4

The dependence on temperature of the voltammetric behavior of Pt(111), Pt(100), and Pt(110) electrodes in 0.1 M HClO4 has been studied. A thermodynamic analysis of the hydrogen underpotential deposition (HUPD) has been carried out, taking into account that the adsorption process is accompanied by changes in the electrode double layer. The analysis for Pt(100) requires a previous deconvolution of the OH adsorption contribution whereas for Pt(110), the analysis is limited to high H coverages. The Pt−H bond energy values obtained for the Pt(hkl) electrodes agree with the values obtained in UHV. On Pt(111) and Pt(100), Δ (HUPD) changes linearly with coverage, with Frumkin repulsive parameters 27 and 9 kJ mol-1, respectively. The values obtained for Δ (HUPD) (−48 J mol-1 K-1 for Pt(111), − 56 J mol-1 K-1 for Pt(100), and from −55 to − 70 J mol-1 K-1 for Pt(110)) suggest immobile hydrogen adsorption. The fact that Δ (HUPD) depends significantly on the crystallographic orientation suggests that the symmetry of t...

Investigation of electrochemical double-layer (ECDL) capacitors electrodes based on carbon nanotubes and activated carbon materials

The carbon nanotubes (CNT) show promising electrochemical characteristics particularly for electrochemical energy storage. The electrochemical double-layer (ECDL) capacitor is a new type of capacitor with features intermediate between those of a battery and a conventional capacitor. ECDL capacitors have been made using various types of CNT and activated carbon (a-C) as electrode material. The specific capacitance per surface area of the electrodes depends on the thickness and the specific surface area of the active material. The CNT electrodes show a specific capacitance from 0.8 and 280 mF cm −2 and 8t o 16 Fc m −3 , respectively. Increasing the mass density also helps to increase the capacitance. Commercially available activated carbon (a-C) electrodes were also tested in order to study their specific capacitance as a function of their physical properties. The various a-C electrodes have specific capacitance per surface area ranging from 0.4 to 3.1 F cm −2 and an average specific capacitance per volume of 40 F cm −3 due to their larger mass density.

Scanning electron microscopic studies of porous carbon electrodes used in alkaline fuel cells

Multilayer, polytetrafluoroethylene (PTFE)-bonded gas diffusion-type electrodes were prepared by the rolling method. Changing the electrode structure and manufacturing method improved alkaline fuel cell performance. Activated carbon or carbon black was used as the support material, with platinum as a catalyst and nickel screen as the backing material. Double-layer electrodes possessed both active and diffusion layers on the backing layer. However, the single-layer electrodes had only the active layer on the backing layer. The electrodes were prepared by using different PTFE contents and platinum loadings. In this study the surface photographs of the electrodes were taken with a scanning electron microscope. Elemental analyses of the surface elements were performed by energy dispersive X-ray spectroscopy (EDXS). Electrodes having activated carbon on their surfaces were observed to possess a nonuniform and porous structure. These electrodes showed better performance than electrodes having carbon black, which presented a uniform and nonporous structure.

Heat-treatment retention time dependence of polyvinylidenechloride-based carbons on their application to electric double-layer capacitors

The heat-treatment retention time effect of carbonized polyvinylidenechloride (PVDC) was investigated. Homogeneous PVDC with a crystallite size of 267 Å was used as a precursor material for an electric double-layer capacitor electrode. The P-120m material, which was heat treated for 120 min at 700 °C, shows a larger specific capacitance than any other material in this study. It shows the largest values reported up to now, reaching values as high as 100.2 F/g for a two-electrode system, which is equivalent to 400.8 F/g in a conventional three-compartment electrode system. It is difficult to distinguish the difference in the pore-size distribution by way of gas adsorption as the retention time is varied. However, the difference can be clarified using a novel method based on the analysis of transmission electron microscopy images. As the retention time for heat treatment increases, the pore size grows through the coalescence of small pores. Furthermore, a new concept for the electric double-layer capacitance is suggested on the basis of analysis of the transmission electron microscopy observations.

The capacitance of the electric double layer of electrodes in molten salts

High exchange current electrodes are reversible electrodes with an exchange current density greater than 0.1 A cm −2. Both in the time and frequency domains, their behaviour is predominantly inductive. Using the inductive model of high exchange current electrodes developed earlier, the double layer capacitance of a liquid Mg electrode in a melt composed of 20 mol% of MgCl 2 and 80 mol% of NaCl or KCl, is evaluated. As in aqueous electrolytes, the double layer capacitance is a sum of the compact and the diffuse layer capacitances. A model of the electric double layer of electrodes with high exchange current density is proposed, which allows for the calculation of the compact layer capacitance. It has been assumed in this calculation that the compact layer of the electric double layer is composed of a primary ionic shell, formed by specifically adsorbed chloride anions. The capacitance of such a layer is calculated as the Helmholtz capacitance, with the dielectric permittivity equal to 1. This capacitance is then corrected for the exchange current density. The corresponding amount of counterions to the specifically adsorbed anions in the primary ionic shell, is transferred to the neighbouring holes, creating the diffuse layer. The capacitance of the diffuse layer is thus calculated from the experimentally evaluated double layer capacitance and calculated by the present model compact layer capacitance.

Electrochemical impedance spectroscopy of polynucleotide adsorption

The dependence of the impedance of the electrode double layer of mercury electrode on frequency around the potentials of the tensammetric peaks of single-stranded and double-helical polynucleotides and DNA was studied. From the frequency dependence of the impedance of the electrode double layer represented in a complex plane impedance plot, the electric equivalent circuit of the electrode covered with adsorbed DNA layer was determined. It was concluded that the desorption of denatured ssDNA is accompanied by higher dielectric losses than the desorption of native dsDNA. This can be explained by the higher flexibility of ssDNA compared to the dsDNA. The capacitance peak of single-stranded polyadenylic acid (poly A) observed at pH 8 around −1.3 V splits at low frequencies in two peaks.

Impedance Analysis of DNA and DNA-Drug Interactions on Thin Mercury Film Electrodes

In this review we briefly summarize the results of impedance measurements (dependence of the differential capacitance C and/or impedance Z of the electrode double layer on potential E, C-E curves) or on frequency (Electrochemical Impedance Spectroscopy-EIS) of nucleic acids at mercury film electrode (MFE). Mercury film was plated either on a glassy carbon electrode (GCE) or pyrolytic graphite electrode (PGE). The dependence of the pseudocapacitance redox peak of echinomycin on concentration and on the ac voltage frequency was measured in bulk solution. Interaction of single- and double-stranded DNA with bis-intercalator echinomycin at nucleic acid-modified surface was studied using EIS with adsorptive transfer method.

Interaction of DNA with echinomycin at the mercury electrode surface as detected by impedance and chronopotentiometric measurements

The capacitance measurement (dependence of the differential capacitance C of the electrode double layer on potential E, C– E curves), electrochemical impedance spectroscopy (frequency response of the impedance Z of the electrode double layer—EIS) and constant current chronopotentiometry (dependence of d t/d E on potential at constant current, chronopotentiometric stripping analysis—CPSA) have been used for electrochemical study of echinomycin and its interaction with single-stranded (ss) and double-stranded (ds) DNA at the hanging mercury drop electrode (HMDE). The capacitance measurement showed that echinomycin gives a pseudocapacitance redox peak strongly dependent on the a.c. voltage frequency at the potential of −0.53 V. This peak is observed with dsDNA-echinomycin complex as well, but not with ssDNA treated by echinomycin. Similar results were obtained using CPSA measurements. Thus capacitance measurements and CPSA can distinguish with the aid of the bis-intercalator echinomycin the single-stranded and double helical form of DNA adsorbed at the mercury electrode surface. Impedance measurement in connection with adsorptive transfer technique can find the differences between ssDNA and dsDNA, which promise to use this technique for detection of dsDNA in hybridisation reactions.

Effect of structure of the electrical performance of gas diffusion electrodes for metal air batteries

The effects of different commercial carbon powders (Vulcan XC72R, Black Pearls 3700 and Shawiningan Black), on the performance of double-layered gas diffusion electrodes are reported. The active mass was catalysed with cobalt tetramethoxyphenylporphyrin. Various techniques such as impregnation, permeation, porosimetry, SEM observations and impedance spectroscopy were used to characterise the structure of the electrodes. The electrochemical behaviour was determined by means of polarisation curves in alkaline electrolyte. The catalytic activity and the physical characteristics of the carbon material strongly affect the performance and the life of the electrodes. The results significantly contribute to the proper selection of carbon materials and to optimisation of the electrode manufacturing technology. Besides the estimation of some structural parameters enables the correct simulation of electrode behaviour.