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We report herein on a study of the electrical double layer capacitance of microporous activated carbon fibers electrodes as a function of the concentration of the electrolyte in aqueous solutions. The accessibility of the subnanopores in the electrode-to-ion adsorption decreases as the ionic strength of the solutions decreases, due to the increase in the hydration shell of the ions. Evaluating the concentration effect on the effective size of the ions was possible by the use of highly selective carbon molecular sieve electrodes, produced by the chemical vapor deposition (CVD) of carbon on the ACF surface, which partially closes the entries to the pores. The CVD process was carried out by the pyrolysis of benzene. This study provides a basis for the rigorous evaluation of the size of solvated ions in solutions at different levels of solvation.

In this study, we present the positive effect of 1,10-phenanthroline as an electrolyte additive that is strongly adsorbed on activated carbon electrodes, thereby adding effective redox activity to their initially capacitive interactions with electrolyte solutions. We obtain a stable capacitance of 320 F/g for the negative electrode and 190 F/gelectrodefor full symmetric supercapacitor cells, operating up to 3.4 V in nonaqueous media, during many thousands of cycles. This corresponds to a specific capacity of 180 (mA h)/gelectrode. The high voltage and capacity of these systems can pave the way for developing high-energy-density pseudocapacitors that may be able to compete with battery systems. We explored the mechanisms of the electrode interactions using electrochemical tools, including impedance spectroscopy.

The electrodepostion of bi-valent iron, zinc and tungsten (IV) on tungsten electrodes in equimolar NaCl-KCl melt at 700-750oC was studied by Cyclic Voltammetry and Chronoamperometry. While iron (II) and zinc (II) ions demonstrate regular values of diffusion coefficients, which are all in the range of 10-6-10-5 cm2/sec, tungsten (IV) ions diffuse considerably slower. Plausible process mechanisms were proposed, according to which the tungsten (IV) ions form polynuclear ions and these massive species diffuse at considerably more moderate rates.

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.

The preparation of modified, catalytically active, functional carbon electrodes and their application to the electrochemical reduction of trinitrotoluene (TNT) is reported. Modification of the electrodes is performed with composites of nanometer‐sized, mesoporous titanium dioxide, which acts as a support containing inserted/deposited nanoparticles of ruthenium, platinum, or gold. These composites are prepared by a novel sonochemical synthesis using simple and low‐cost precursors. Cyclic voltammetry shows that 2,4,6‐trinitrotoluene can be reduced on thus‐modified carbon‐paper electrodes at potentials of around –0.5 V (vs. Ag/AgCl/Cl–) in aqueous solutions. Unexpectedly, carbon‐paper electrodes modified with the TiO2/nano‐Pt composites demonstrate a remarkable electrochemical activity toward the reduction of trinitrotoluene. A significant finding is that the two electrode processes—the reduction of TNT and of oxygen—are quite well separated in potential on the modified carbon‐paper electrodes because of selective electrochemical activity of the TiO2/nano‐Pt and TiO2/nano‐Au composites. TiO2/nano‐Ru composites are found to be much less electrochemically active for the detection of TNT compared to the previous two. It was also established that the titanium dioxide support of TiO2/nano‐Pt composites plays a specific role for facilitating the TNT‐ and oxygen‐reduction processes.

A combination of ab initio calculations and experimental methods (high-resolution neutron and powder X-ray diffractions) was used to solve the crystal structure of MgxMo6S8(x1 and 2). It was shown that at room temperature, the latter are similar to the crystal structure of classic Chevrel phases (CPs) such as CuxMo6S8:? space group R, ar6.494 Å, 93.43° for MgMo6S8and ar6.615 Å, 95.16° for Mg2Mo6S8. For x1, one Mg2cation per formula unit is distributed statistically between inner sites. For x2, the second Mg2cation per formula unit is located in the outer sites. Peculiarities of the electrochemical behavior of the CPs as electrode materials for Mg batteries were understood on the basis of the analysis of the interatomic distances. It was shown that the circular motion of the Mg2ions between the inner sites in MgMo6S8is more favorable than their progressive diffusion in the bulk of the material, resulting in relatively slow diffusion and Mg trapping in this phase. In contrast, in Mg2Mo6S8, the repulsion between the Mg2ions located in the inner and outer sites facilitates their transport through the material bulk.

Chevrel phases (CPs), MxMo6T8(M metal, T S, Se), may be used as unique cathode materials for rechargeable Mg batteries because they ensure the high mobility of multivalent cations. However, the electrochemical behavior is strongly affected by the host composition. For the selenide, the intercalation process is completely reversible, while partial Mg trapping occurs upon its extraction from the sulfide at room temperature. A combination of powder X-ray and high-resolution neutron diffraction was used to study the crystal structure of triclinic MgMo6Se8, especially for determining the precise location of the Mg2cations within the host lattice. It was shown that the crystal structure of the selenide is similar to that of triclinic Fe2Mo6S8:  The Mg2cations are distributed between two sites (per formula unit) with a square-pyramidal anion coordination. The environment analysis of all the cation sites based on the bond valence sum theory led us to propose the most favorable routes for Mg2ion transport, as well as to explain the peculiarities of the electrochemical behavior of the CPs as intercalation materials for Mg batteries.

We previously showed that, for neutral electrolytes of small cations and relatively larger anions, it is possible to design certain pore sizes in active carbons that are large enough to electroadsorb cations but too small to allow anion electroadsorption. This situation leads to an electrical double-layer (EDL) capacitance that is significant only at potentials that are negative to the potential of zero charge (PZC); hence, much smaller capacitance is measured at potentials positive to the PZC. It was found that when the electrolyte is a strong acid (e.g., H2SO4, HCl), a considerable capacitance is observed at positive potentials, even when the average pore size is too small to allow the insertion of large anions in neutral electrolyte solutions. This effect disappears when the pore size becomes considerably larger than the size of the ions. In this case, the EDL capacitance at positive potentials for both neutral and acidic solutions is comparable. The following four-step mechanism was found to comply best with the experimental data:  (1) By acid catalysis, the protons form carbonium species within the conjugated carbon network. (2) The anions react with the carbonium ions, providing uncharged species in an activated state, which are chemibound as surface groups to the walls of the pores. (3) Because these surface groups are effectively much smaller in size than are the charged ions, they can migrate by chemical bond exchange within the carbon skeleton via constrictions (known to exist in microporous and molecular sieving carbons), which are too narrow to accommodate hydrated charged species. (4) Upon reaching wider spaces, the uncharged species are reionized and solvated by water molecules, which can fill small pores. The justification for the above mechanism is thoroughly discussed and demonstrated by the experimental results.

Abstract In the present study, we explored how milling Mo6S8 Chevrel phase in inert or air atmosphere affects their electrochemical behavior as a Mg-ion insertion material for rechargeable Mg batteries. Electrochemical tools such as slow scan rate cyclic voltammograms and potentiostatic intermittent titration technique have been used in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. In contrast to the deterioration observed for milling Mo6S8 in air, it’s milling under Ar results in specific capacity increase due to improved Mg-ion diffusion kinetics. It was shown that in spite of the conservation of the bulk crystallographic structure, both for air and the Ar-milled materials, they differ significantly in the average particle sizes and the degree of surface oxidation state.

We explored routes for the synthesis of LiMn 2O 4 spinel from five different polymorphs of MnO 2 as the manganese source. These included α and β-MnO 2 and three types of γ MnO 2 (electrochemically produced EMD, and two types of chemically produced CMD). The synthesis included a lithiation step by mild reduction of the MnO 2 with glucose in a LiOH solution, followed by calcination of the lithiated product. This route was shown in a previous study to produce highly pure, nanocrystalline LiMn 2O 4. The effect of the application of ultrasound radiation in the lithiation step on the quality of the products was also explored. It was found that the degree of lithiation, the purity of the Li xMn 2O 4 spinel phase obtained and its electrochemical behavior as a Li insertion electrode material depend strongly on the nature of the MnO 2 material in terms of crystal structure and morphology. The effect of ultrasound radiation was found to be detrimental. A very good electrochemical performance (capacity, stability) in repeated Li intercalation–deintercalation cycling was obtained with LiMn 2O 4 originating from nanometric CMD. The tools for this study included XRD, TEM, surface area measurements (BET method), atomic absorption and standard electrochemical techniques (voltammetry, chronopotentiometry).

Advantageous electrolytic solutions for rechargeable magnesium batteries are obtained by dissolving in THF the reaction products of EtAlCl2 and Bu2Mg, in various stoichiometric proportions. The components of these solutions are identified by multinuclear NMR (¹H, ¹³C, ²⁷Al, and ²⁵Mg) and conductivity measurements for the closely related system where the organomagnesium species is Et2Mg. The system with the highest electrochemical stability and relatively high ionic conductivity, denoted as a “2:1 complex”, is obtained from a 2:1 ratio of EtAlCl2 and Et2Mg and is shown to be composed of a chloride-bridged species, Et2ClAl−Cl−AlClEt2^-, and of MgCl⁺, the result of transmetalation reactions.

The influence of leaching chemistry on the performance of Mo6S8 cathodes for rechargeable Mg batteries was studied by XRD, XPS, and electrochemical methods. It is shown that Cu2Mo6S8, chemically leached in I2/AN (acetonitrile) or in HCl/H2O, is able to accommodate the theoretical amount of Mg²⁺ ions upon the first discharge of the electrode (two Mg atoms per formula unit). In contrast, the process of Mg extraction upon charging the electrode cannot be completed at room temperature, resulting in capacity loss between the first and subsequent cycles. Electrochemical experiments at elevated temperatures reveal that the capacity loss is not related to the leaching process, but results from an intrinsic kinetic problem of the Mg extraction from the MgMo6S8 phase. Despite the initial capacity loss, the materials leached in I2/AN or in HCl/H2O show excellent stability upon long-term cycling, with a specific capacity of 90−100 mA·h/g.

Electrochemical impedance spectroscopy is used to characterize thin p-doped polypyrrole (PPy) films in propylene carbonate (PC) solutions and poly(trifluorophenyl)thiophene (PTFPT), in solutions based on sulfolane (SF). It appears that the latter film is much less swelled compared to the former one. One consequence of this difference is that the PTFPT film shows a much higher bulk resistance compared to that for the PPy film. Another important consequence is that the swelling of the PTFPT film is essentially physically non-homogeneous. Two parallel, uncoupled paths, with different chemical diffusion coefficients, model the experimental results adequately. In order to quantify the impedance spectra for both polymer films, we use a model proposed by Rubinstein et al.explaining the difference in the diffusion coefficients of Ru(bpy)3+/2+3within a thin Nafion film. The model can also predict the impedance spectra for composite powdery electrodes containing different particle sizes, such as composite cathodes and graphite anodes used in lithium batteries.

A careful study of electrochemical lithiation of a composite graphite electrode at elevated temperatures was performed using a potentiostatic intermittent titration technique. Special emphasis was placed on the stage 4 to stage 3 phase transition, occurring in the range of x (in Li xC 6) between 0.12 and 0.22 (this corresponds to the partial dimensionless intercalation level ? ranging from 0 to 1). An abrupt increase in the Li chemical diffusion coefficient, D chem, when approaching the relative coverage level ?=1/3, and a specific non-Arrhenius shape of the plot of D chem vs. the inverse of the absolute temperature were observed. These two features of the phase transition seem to be in agreement with a recent thermodynamic model for adatoms diffusing on a surface with two considerably different barrier energy sites.

Polypyrrole (PPy) films obtained by low-current galvanostatic polymerization of pyrrole in propylene carbonate solutions exhibit excellent reversibility, high anodic stability, and, at the same time, a characteristic change in the shape of the voltammetric response and an increase in the film's doping level during long-term potentiodynamic cycling. To understand the behavior of PPy films, we performed their characterization by in situ atomic force microscopy, which shows drastic changes in the micromorphology (and its dynamics) of freshly prepared and long-term cycled PPy films. In addition, a parallel study of the same PPy film was performed by electrochemical quartz crystal microbalance (EQCM), to correlate micromorphological changes in the films occurring as a result of continuous cycling with their ion-exchange mechanism. The morphological and mass changes are discussed in light of the fact that there are chemically different structures of PPy and in terms of a conformational relaxation model.

A new synthetic method has been developed and demonstrated for the utilization of commercially cheap MnO2 for the production of nanoparticles of LiMn2O4 spinel as a cathode material for Li-ion batteries. The process involves the insertion of lithium into electrolytic manganese dioxide (EMD) in an aqueous medium with glucose as a mild reductant in open air. The material resulting from calcination is pure, spinel-structured Li0.96Mn2O4 particles of sub-micrometric and nanometric size that exhibit promising electrochemical behavior in nonaqueous Li-salt solutions. Further development of this process may be interesting for the commercial production of LiMn2O4 for Li-ion batteries.

Metallic magnesium can be reversibly deposited from ethereal solutions of magnesium−aluminum complex salts of the general structure Mg(AlCl4-nRn)2, where R = alkyl. In contrast to the case of lithium surfaces, already thoroughly investigated, the surface state of magnesium electrodes in contact with organic solutions is yet unclear. In this paper we report on a systematic surface analysis of magnesium electrodes in contact with various organic solutions, using XPS. We find in both clean tetrahydrofurane (THF) and THF solutions of dibutylmagnesium or butylmagnesium chloride that the metal surface consists of magnesium oxide and hydroxide (probably developed during manipulation and sample transfer); however, it does not develop thick passivation layers. In THF solutions containing Mg(AlEtBuCl2)2, surface residuals of carbon, aluminum, and chlorine are detected yet are restricted to the outermost part of the surface, as physically adsorbed species. From their concentration one deduces that both the complex salt and the ether are not reduced at the magnesium surface but precipitate as an insoluble film. Metallic magnesium deposited from THF/Mg(AlEtBuCl2)2 solution on gold electrodes shows a very similar surface chemistry, providing an additional proof that, even in the most frail conditions available during electrochemical deposition, pure magnesium is deposited. The surface chemistry of magnesium in contact with propylene carbonate (PC) exhibits as well layered surface chemistry, most of it composed of magnesium oxide and hydroxide, but no evidence is found for reduction products of PC. It is concluded that the magnesium metal behaves like a surface film-free electrode in organo-haloaluminate/THF solutions. Our conclusions support several other studies on the properties of magnesium in such solutions.

Specially prepared, thin poly-3-3,4,5-trifluorophenylthiophene, PTFPT, films were shown to possess stable p- and, most importantly, n-doping in TEABF4sulfolane SF solutions. Electrodes comprising PTFPT films were studied by cyclic voltammetry CV, potentiostatic intermittent titration PITT, and electrochemical impedance spectroscopy EIS. A detailed analysis of the shape of the time-dependent current transients during PITT characterization of the PTFPT electrodes has been performed. The non-uniform character of the PTFPT film doping was proved. Plots of dlogItdlog tvs.tτdwere found to be useful for understanding the response of potentiostatic transients. The Cottrell time domain during potentiostatic transients was found to be very narrow, reflecting the drastic effect of the Ohmic potential drops mainly across the film's bulk on the semi-infinite diffusion current transient at the shortest times, and a wide distribution of the diffusion time constants. PITT and EIS characterizations provided converging results with respect to the relevant diffusion time constants and the non-uniform character of PTFPT film doping in the SF solution. EIS measurements were found to be very useful for the determination of diffusion time constants, as they allow more effective separation of the medium frequency, Warburg response from the Ohmic and the kinetic high-frequency responses.

Specially prepared, thin poly-3-(3,4,5-trifluorophenyl)thiophene, PTFPT, films were shown to possess stable p- and, most importantly, n-doping in TEABF₄/sulfolane (SF) solutions. Electrodes comprising PTFPT films were studied by cyclic voltammetry (CV), potentiostatic intermittent titration (PITT), and electrochemical impedance spectroscopy (EIS). A detailed analysis of the shape of the time-dependent current transients during PITT characterization of the PTFPT electrodes has been performed. The non-uniform character of the PTFPT film doping was proved. Plots of dlog|I(t)|/dlog t vs. t/τ_d were found to be useful for understanding the response of potentiostatic transients. The Cottrell time domain during potentiostatic transients was found to be very narrow, reflecting the drastic effect of the Ohmic potential drops (mainly across the film's bulk) on the semi-infinite diffusion current transient at the shortest times, and a wide distribution of the diffusion time constants. PITT and EIS characterizations provided converging results with respect to the relevant diffusion time constants and the non-uniform character of PTFPT film doping in the SF solution. EIS measurements were found to be very useful for the determination of diffusion time constants, as they allow more effective separation of the medium frequency, Warburg response from the Ohmic and the kinetic high-frequency responses.

The behavior of composite graphite electrodes used as anodes in Li-ion batteries, in repeated lithium intercalation−deintercalation processes, largely depends on the solution's composition. Failure mechanisms of graphite electrodes were studied in selected solutions using in situ imaging by atomic force microscopy. Of special interest is the stable behavior of lithiated graphite electrodes in ethylene carbonate solutions, while in solutions of a very similar solvent, propylene carbonate (PC), lithiated graphite electrodes fail. The morphological studies reported herein seem to confirm that the major failure mechanism of graphite electrodes in PC solutions involves cracking of the particles and electrical isolation of most of the active mass by surface films, rather than a massive exfoliation of the graphite particles due to cointercalation of solvent molecules. Cracking of the graphite particles during cathodic polarization depends on the crevices that originally exist in some types of graphite particles, especially in synthetic materials, and is promoted by gas formation within the crevices, due to the reduction of solvent molecules.

This paper reports on our recent attempts in the characterization of n-doping of polythiophene (PTh) and p-doping of polypyrrole (PPy) for their use as the anode and cathode, respectively, for rechargeable batteries. N-doping of PTh with large (TEA) cations was studied by combined application of cyclic voltammetry, in situ conductometry and ex situ atomic force microcopy (AFM). The average potential for n-doping of PTh was close to 1.2 V (versus Li/Li⁺). Substantial trapping of negatively charged polarons was observed during consecutive n-doping. Addition of Li-salt to the background electrolyte, even in a small concentration, resulted in the almost complete deactivation of the film with respect to n-doping. We suggest that the above drawback can be overcome by using the more robust fluorosubstituted polyphenyl(thiophene), P3FPhTh. On the other hand, when addressing polymer cathodes, specially prepared PPy films showed highly reversible behavior and a large capacity of up to one electron per ring (or 420 mAh per gram of neutral polymer) when cycled up to 4.6–4.7 V (versus Li/Li⁺). Only above 5 V (versus Li/Li⁺) did an irreversible over-oxidation of PPy occur. Electrochemical characteristics of p-doped PPy cathode are compared with that of lithiated V2O5 film. Two possible alternative ways for changing the dopants in p-doped PPy, from anions to cations, are discussed. Copyright © 2003 John Wiley & Sons, Ltd.

Nanoparticles of SnO were synthesized sonochemically in mildly basic SnCl2 solutions. The amorphous product thus obtained could be transformed to a nanocrystalline phase by heating to 200 °C. Composite electrodes comprised (by weight) of 80% SnO, 10% graphite flakes (conductive additive), and 10% polymeric binder (an optimal composition) were tested as anodes for rechargeable Li batteries. The nanocrystalline SnO was found to be much more effective as an active material for electrodes than the initial amorphous phase. These electrodes could reach nearly their theoretical capacity (≃790 mAh/g, SnO) in electrochemical lithiation−delithiation processes versus a Li counter electrode in nonaqueous Li salt solutions. However, there is still a long way to go to the possible use of SnO as an anode material in practical batteries. This is due to its high irreversible capacity (Li2O formation and surface film precipitation due to reactions of lithium−tin compounds with solution species) and gradual capacity decrease during repeated charge−discharge cycling. Possible reasons for this capacity fading are discussed. The tools for this study included electron microscopy (both TEM and SEM), thermal analysis (DSC), XRD, FTIR and impedance spectroscopies, and standard electrochemical techniques.

This paper reports on our recent attempts in the characterization of n‐doping of polythiophene (PTh) and p‐doping of polypyrrole (PPy) for their use as the anode and cathode, respectively, for rechargeable batteries. N‐doping of PTh with large (TEA) cations was studied by combined application of cyclic voltammetry, in situ conductometry and ex situ atomic force microcopy (AFM). The average potential for n‐doping of PTh was close to 1.2 V (versus Li/Li+). Substantial trapping of negatively charged polarons was observed during consecutive n‐doping. Addition of Li‐salt to the background electrolyte, even in a small concentration, resulted in the almost complete deactivation of the film with respect to n‐doping. We suggest that the above drawback can be overcome by using the more robust fluorosubstituted polyphenyl(thiophene), P3FPhTh. On the other hand, when addressing polymer cathodes, specially prepared PPy films showed highly reversible behavior and a large capacity of up to one electron per ring (or 420 mAh per gram of neutral polymer) when cycled up to 4.6–4.7 V (versus Li/Li+). Only above 5 V (versus Li/Li+) did an irreversible over‐oxidation of PPy occur. Electrochemical characteristics of p‐doped PPy cathode are compared with that of lithiated V2O5film. Two possible alternative ways for changing the dopants in p‐doped PPy, from anions to cations, are discussed. Copyright © 2003 John Wiley & Sons, Ltd.

In an attempt to form a proton-selective environment in porous carbons that is similar to that of proton-conducting polymers, we used highly oxidized molecular sieving carbons that are covered by oxygen-containing surface groups. Naturally, it would be assumed that the free electron pairs of the surface oxygen atoms are those that provide specific adsorption sites for protons. However, we discovered that selective adsorption of protons takes place within the pores of the molecular sieving carbon electrode, even in the absence of surface oxides.

Electrolytic mixtures of vanadium(V) oxide and β-NaxV2O5bronze were synthesized and studied by X-ray diffraction and thermal analyses, step galvanostatic titration, IR absorption spectroscopy, mass spectroscopy, and electrochemical methods.

This paper deals with the correlation between the real structure of Cu2Mo6S8 chevrel phase (CuCP) and its electrochemical behavior as a cathode material in novel, promising rechargeable Mg batteries. To obtain fast kinetics of Mg insertion into this material, its particle size was reduced to sub-micrometer scale by milling. We discovered an unusual instability of CuCP upon milling, which leads to a drastic decrease in the electrode capacity. The mechanism of this mechanical instability was investigated by XRD and XPS. The comparison of the CuCP mechanical stability with that of other chevrel phases (Ni, Sn, Pb, or Ag instead of Cu) reveals that the unusual behavior of CuCP is connected to the unstable oxidation state of the copper ions in this material. It was shown that milling of CuCP leads not only to an unusually deep amorphization of the material but also to a chemical reaction in which the Cu⁺ ions are reduced and removed from the CuCP lattice.

To determine the mechanism responsible for the formation of electrolytic sodium–vanadium oxide bronze e-NaxV2O5, synthesized earlier from acid vanadyl sulfate electrolyte, β-bronze i-NaxV2O5is synthesized by exposing electrolytic oxide e-V2O5in the same sodium-containing electrolyte under open-circuit conditions, with a subsequent annealing of the sample. It is established that the two modifications of β-bronze (e-NaxV2O5and i-NaxV2O5) are identical and that electrolytic precursors of β-bronze NaxV2O5form via an ion-exchange mechanism.

Certain microporous carbons have pores of molecular dimensions, the size of which can be adjusted over a wide range to fit the dimensions of a large variety of molecules. With knowing the dimensions of these molecules, size-calibrated porous carbons can be produced. In this work, we took advantage of the electronic conductivity of carbon in using it as an electrode in electrolytic solutions. By changing the electrode potential, we could induce electroadsorption and electrodesorption of ions of different dimensions into pore-calibrated carbons, thus enabling us to estimate effective ion sizes. A few fundamental questions such as whether ions accommodated in the electrodes' pores are in a solvated state, which is important for novel electrochemical energy storage devices and for microbiological systems, could be addressed. Analysis of the results indicates that all the cations that are employed are electroadsorbed in the electrode pores in hydrated states. Compared with the monovalent cations, the bivalent cations exhibit dimensions that make them almost twice as big. Monovalent anions are basically adsorbed in a nonhydrated state. The doubly charged sulfate anion is adsorbed in the hydrated state. The nitrate, a multiatom planar anion, has a smaller effective dimension than the monoatomic halogen anions, in accordance with the observation that the pores in many activated carbons are slit-shaped. The analysis of the results enabled us to establish a scale of ionic effective dimensions in aqueous media, as presented below (MTBE stands for methyl tert-butyl ether):  cations, [3.62 Å, N2] < Cs⁺ < K⁺ < Na⁺ < Li⁺ < [4.21 Å, CF4] < [5.05 Å, SF6] < [5.8 Å, MTBE] < Ba²⁺, Ca²⁺, and Mg²⁺; anions, [3.62 Å, N2] < NO3^- < Cl^- < F^- < Br^- < [4.21 Å, CF4] < ClO4^- < [5.05 Å, SF6] < [5.8 Å, MTBE] < SO^2-. We discovered that as long as the pore size is considerably greater than the ion size, the electric double-layer capacity at moderate concentrations is independent of both the size and charge of the ions in solutions.

The possibility for electrochemical modification of the surface functional groups of a self-assembled siloxane-anchored monolayer was explored. The primary challenge of this work was to minimize the insulating silicon oxide layer while still providing ample hydrophilic oxide for anchoring siloxane-based monolayers. Working on highly doped silicon electrodes, wetting measurements and scanning probe microscopies (both atomic force microscopy and lateral force microscopy) were combined with electrochemical measurements to evaluate various surface preparations in terms of their suitability for combining electrochemical activity with smooth uniform surfaces on which successful monolayer formation can be achieved. The difficulties encountered in achieving this balance suggest that organic electrochemistry on an oxidized silicon surface will be difficult to achieve, in the presence of even a thin oxide layer.

In this paper we present a new approach to the analysis of electrochemical impedance spectroscopy (EIS) data for electrodes covered by passivating surface films that grow in time. The impedance of such electrodes increases in time due to the gradual growth of their thickness as well as to the change of their local characteristics. The growing part of the surface films may either be homogeneous in its structure and properties or inhomogeneous, with gradually changing properties as a function of the distance of the newly formed surface species from the metal−film interface. We show herein that the time−difference impedance spectra (DIS), i.e., the difference between two complex impedance curves, Z(ω, t1) − Z(ω, t2), measured after different periods of storage, t1 and t2, as a function of frequency may provide a very useful tool for characterizing the nature of the growing passivating films. These time−difference impedance curves (e.g., plotted in coordinates Zimag vs Zreal) can be simulated both for homogeneous growing surface films on electrodes and for situations in which local properties such as the surface film's resistivity are nonuniform across the growing film. The prospects of this approach have been demonstrated in the analysis of the surface films at lithium electrodes freshly prepared and stored in alkyl carbonate mixture (ethylene−dimethyl carbonates) with a Li salt, and measured periodically by EIS. The analysis of DIS of this system has shown that during a period of several hours after the electrode's preparation in solution, the process of the surface film deposition is very complicated. Properties of the new portions of the film are varying in time so that the deposited film possesses a highly nonuniform structure. Moreover, the local characteristics of earlier formed portions are modified gradually inside the film. However, as the storage time is longer, the growth of the surface films on the lithium electrodes becomes more homogeneous, probably due to the increased selectivity of the Li-solution reactions when the surface films are thicker.

The morphology of lithium electrodes in a variety of alkyl carbonate solutions was studied using in situ atomic force microscopy (AFM). We made use of a workstation specially built for the study of highly reactive electrochemical systems by AFM and other scanning probe techniques, based on an evacuable, vibration-protected glovebox. The electrolyte solution used was composed of propylene carbonate (PC), mixtures of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and Li salts from the following list:  LiPF6, LiClO4, LiAsF6, LiN(SO2CF3)2, LiN(SO2CF2CF3)2, and LiC(SO2CF3)3. We studied the effect of solution composition, prolonged storage, Li deposition, and dissolution at low and high current densities. The AFM imaging of these systems shows the complicated morphology of the Li electrodes that depend on the solution composition. We were able to clearly follow the nonuniform nature of Li deposition and dissolution in these systems. We were also able to follow by in situ AFM imaging critical events such as the onset of dendrite formation and the breakdown and repair of the surface films on lithium during Li dissolution at high current densities. The basic morphology of Li electrodes in alkyl carbonate solutions and the condition for the reversible behavior of Li electrodes is discussed.

SnO2 semiconductor nanoparticles were synthesized by an ultrasonic irradiation of an aqueous solution of SnCl4 and azodicarbonamide under ambient air. These nanoparticles are ~3−5 nm in size, as calculated using the Debye−Scherrer formula, and as observed by TEM. The SnO2 nanoparticles were also characterized by powder X-ray diffraction (XRD), reflection spectroscopy and FT-IR spectroscopy, transmission electron microscopy (TEM), DSC, and TGA. The band gap was calculated from reflection spectroscopy. Electrochemical tests were performed using the SnO2 nanoparticles as the electrode's materials in nonaqueous Li salt solutions. The results showed promising reversibility, cycle life and high capacity for lithium insertion into the SnO2 nanoparticles.

Uniformly dispersed amorphous nanoparticles of magnetite in polyvinyl alcohol have been obtained by ultrasound radiation. The properties of the as-prepared composite material were characterized by various analytical methods. We have found that the magnetite particles that were 12–20 nm in diameter were very well dispersed in the PVA. The magnetization measurements establish that the composite material is superparamagnetic in nature.