Electrochemical Transport Properties Research Articles

A search for a single-ion-conducting polymer electrolyte: Combined effect of anion trap and inorganic filler

Lithium trifluoromethanesulfonate:polyethylene oxide (PEO) polymer electrolytes modified by 1,1,3,3,5,5- meso-hexaphenyl-2,2,4,4,6,6- meso-hexamethyl-6-pyrrole (C6P) and nanosize silica filler were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and electrochemical means. An increase in the lithium transference number is observed upon incorporation of even a small amount of C6P. Silica facilitates interchain ion hopping in polymer electrolytes and possibly introduces an additional interfacial ion-conduction path without decreasing t +. Stable solid electrolyte interphase resistance (SEI) was achieved in the polymer electrolytes containing calix[6]pyrrole and silica. It was found that lithium single-ion-conductive polymers with good electrochemical stability and ion transport properties have the potential for considerably boosting the performance of lithium/molybdenum oxysulfide all-solid-state thin film batteries.

Conjugated Donor−Acceptor Copolymer Semiconductors with Large Intramolecular Charge Transfer: Synthesis, Optical Properties, Electrochemistry, and Field Effect Carrier Mobility of Thienopyrazine-Based Copolymers

Several conjugated thieno[3,4-b]pyrazine-based donor−acceptor copolymers were synthesized by Stille and Suzuki copolymerizations, and their optical, electrochemical, and field-effect charge transport properties were characterized. The new copolymers, poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine) (BTTP), poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine-alt-2,5-thiophene) (BTTP-T), poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine-alt-9,9-dioctyl-2,7-fluorene) (BTTP-F), and poly(5,7-bis(3-dodecylthiophen-2-yl)thieno[3,4-b]pyrazine-alt-1,4-bis(decyloxy)phenylene) (BTTP-P), had moderate to high molecular weights, broad optical absorption bands that extend into the near-infrared region with absorption maxima at 667−810 nm, and small optical band gaps (1.1−1.6 eV). They showed ambipolar redox properties with low ionization potentials (HOMO levels) of 4.6−5.04 eV. The field-effect mobility of holes varied from 4.2 × 10-4 cm2/(V s) in BTTP-T to 1.6 × 10-3 cm2/(V s) in BTTP-F. These results show that thieno[3,4-b]pyrazine-based donor−acceptor copolymers combine small optical band gaps with fairly high carrier mobilities and thus are promising for organic electronic devices.

Determination of diffusion coefficients of [formula omitted] inside carbon nanopores using the single particle microelectrode technique

The electrochemical and mass transport properties of TEABF 4 in a nanoporous (NP) carbon material, obtained from silicon carbide, was studied using single particles and a microelectrode technique. The carbon particles of size 100–200 μm were studied by cyclic voltammetry and potential step measurements. The effective diffusion coefficients ( D eff) were calculated starting from the asymptotic solutions of Fick’s second law for short and long time regions. The results show that cycling at low sweep rates was needed in order for the electrolyte to penetrate the inner porosity of the particles. The carbon material showed different electrochemical and mass transport properties depending on the applied potential. At negative polarisation, the results suggest that TEA + was adsorbed on the pore wall, however, being transported very slowly inside the pores. The average D eff after cycling at both positive and negative potentials was 1.1(±0.4) × 10 −8 cm 2 s −1, using the Cottrell relation and 1.5(±0.6) × 10 −8 cm 2 s −1, using the radial diffusion solution. The average value of D eff after cycling at negative potentials was 1.7(±0.6) × 10 −8 cm 2 s −1 using both mathematical solutions.

Electrochemical and Other Transport Properties of Nanoporous Track-Etched Membranes Studied by the Current Switch-Off Technique

Measurements of transient membrane potential after current switch-off have been used to study the electrochemical and other transport properties of nanoporous track-etched membranes (pore diameter of 24 nm) in KCl solutions of various concentrations. Due to their identical straight cylindrical pores within the nanorange, those membranes are a suitable object for the studies of fundamentals of nanofluidics. We have developed a theory, which enabled us to interpret the transients of membrane potential in terms of such properties as the ion transport numbers, the membrane diffusion permeability, and the specific chemical capacity. The fitted values have been further interpreted within the scope of the space-charge model and revealed good self-consistency. The dependence of fitted values of the surface charge density on salt concentration was in agreement with the mechanism of fixed charge formation due to the dissociation of weakly acidic groups, and the surface charge density corresponded well to the measurements by an independent method. Thus, our measurements have revealed a quantitative applicability of standard space-charge model to the description of electrochemical phenomena and electrolyte diffusion in straight cylindrical pores of tens of nanometers in diameter. Proceeding from our data, we could estimate the limiting current densities for our nanofluidic system. They have turned out to be more than 2 orders of magnitude lower than usually encountered in microfluidic systems with electro-osmotic fluid delivery. That finding may point to a considerable handicap in the application of such nanofluidic elements in microsystems.

Comparative studies on electrochemical characterization of homogeneous and heterogeneous type of ion-exchange membranes

Interpolymer films of poly-ethylene and styrene-divinyl benzene copolymer were subjected to chlorosulfonation or chloromethylation then amination for the preparation of homogeneous type of cation- or anion-exchange membranes, respectively. Heterogeneous types of ion-exchange membranes were prepared from polyvinyl chloride (PVC) as binder and ion-exchange resin powder in tetrahydrofuran solvent. Membrane potential and conductance measurements have been carried out in NaCl(aq), CuCl 2(aq) and AlCl 3(aq) solutions at different concentrations to investigate the relationship between concentration of fixed charges and electrochemical properties of these membranes. On the basis of the micro-heterogeneous model, describing the micro-structure of the membrane material, the counter-ion diffusion coefficients were estimated. Membrane conductance data, along with values of concentration of fixed ionic site in the membrane, were used for the estimation of the tortuosity factor and salt permeability employing non-equilibrium thermodynamic principles. It was concluded that electrochemical transport properties of homogeneous type of ion-exchange membranes are superior to those for heterogeneous type of ion-exchange membranes. However, both types of membranes are suitable for electrodriven separation of mono-, bi- and tri-valent electrolytes.

In situ preparation of poly(ethylene oxide)–SiO2 composite polymer electrolytes

Amorphous poly(ethylene oxide) (PEO)–SiO2 composites are prepared by in situ reactions that involve the simultaneous formation of the polymer network and inorganic nanoparticles. The polymer matrix is formed by ultraviolet irradiation of a PEO macromer, and silica is produced in situ by the sol–gel method. The PEO–SiO2 composite mixed with LiBF4 is used as a lithium-ion conducting solid electrolyte and electrochemical transport properties such as ionic conductivity and Li+ transference number are measured. A significant increase in the Li+ transference number, up to 0.56, is found together with a slight decrease in the ionic conductivity. The results are interpreted in terms of interactions between the surface OH groups of the inorganic particles, the cations, the anions, and the ether oxygen atoms on the PEO backbone.

Tetrachloro-substituted perylene bisimide dyes as promising n-type organic semiconductors: studies on structural, electrochemical and charge transport properties.

Twisted π-systems: The highly twisted 1,6,7,12-tetrachloro-substituted perylene bisimides possess an improved electron affinity. The nonplanar nature of these molecules facilitates a slipped brickstone-type rather than a columnar stacking of the π-systems, with a potentially useful two dimensional contact feature. These compounds show isotropic charge carrier mobilities as high as up to 0.14 cm2 V−1 s−1 (see graphic).

Electrochemical transport properties of a cone-shaped nanopore: revisited

There are reports in the literature that a single cone-shaped nanopore generated in a polymer foil separating two equally concentrated dilute aqueous potassium chloride solutions can reach high and low stationary electrical conductivity states respectively depending on the sign of the applied electrical potential. On the basis of published data it has been argued (D. Woermann, Phys. Chem. Chem. Phys., 2003, 5, 1853) that this phenomenon can be understood in terms of a well established model describing the electrochemical transport properties of polyelectrolyte membranes (“model of the membrane with narrow pores”). In the present contribution experimental evidence is presented which gives strong support to these arguments using a model system. Based on the “model of the membrane with narrow pores” a composite membrane is constructed mimicking the structure and electrochemical function of an ensemble of conical nanopores. It is found that the characteristic electrochemical transport property of the composite membrane is that of a cone-shaped nanopore.

Electrochemical and Transport Properties of Templated Gold/Polypyrrole-Composite Microtube Membranes

We have been investigating the transport properties of nanotube membranes prepared via the template method. Membranes containing gold (Au) nanotubes prepared by electroless deposition of Au within the pores of commercially available filters have been studied most extensively. The advantage of these membranes is that the inside diameter of the Au nanotubes can be precisely controlled down to molecular dimensions. Currently, we have no other materials synthesis strategy that allows for such precise control over the diameter of the nanotubes obtained. We are interested in developing such chemistries so that nanotubes having any desired inside diameter that are composed of materials other than metals can be prepared. We describe here the electrochemical polymerization of polypyrrole (PPy) microtubes within templated prepared Au microtubes. We demonstrate that the effective inside diameter of the PPy microtubes can be controlled by varying the number of voltammetric scans used during the PPy electropolymerization. The electrochemical characteristics and transport properties of these composite Au/PPy microtube membranes are described here. © 2003 The Electrochemical Society. All rights reserved.

Development of urethane acrylate composite ion-exchange membranes and their electrochemical characterization

With the objective of introducing antifouling characteristics into interpolymer types of cation and anion exchange membranes, the surface of these membranes was coated with a 12-μm-thick urethane acrylate layer and was cured by UV radiation of wavelengths 308 and 172 nm under a complete inert atmosphere. Different urethane acrylate composite ion exchange membranes developed were characterized in NaCl solution by measuring their ion-exchange capacity, volume fraction of water, contact angle with water, membrane conductance, and membrane potential. It was found that the electrochemical transport properties of urethane acrylate composite cation-exchange membranes were increased due to resonance stabilization of the urethane group, which acts as a weak acid and dissociates as a negatively charged urethane ion and a positively charged proton. This contributes toward the net charge density of the membrane matrix responsible for enhanced selectivity and conductivity, while for urethane acrylate composite anion-exchange membranes reduction in net charge density was responsible for reduction in electrochemical transport properties. Counterion transport number, permselectivity, and counterion diffusion coefficient values for these membranes were also estimated. Experiments were also carried out in higher homologs of sodium carboxylate solutions in order to observe the fouling tendencies of these membranes. It was concluded that it is possible to obtain antifouling characteristics of ion-exchange membranes by coating and curing thin hydrophilic layers of urethane acrylate on their surfaces without sacrificing their electrochemical transport properties.

Visualization of particle distribution in composite polymer electrolyte systems

Abstract A simple visualization method is developed to enable the imaging of the distribution and agglomeration of ceramic fillers in composite polymer electrolytes by scanning electron microscopy (SEM). Solvent-free composite electrolytes based on poly(ethylene oxide) (PEO), LiBF4 and SiO2 particles are used as examples. The SiO2 particles are stained by a heavy element (Pb) to enhance the imaging contrast between the particles and their surroundings. Modified SiO2 from a silanization reaction where most of the surface OH groups has been replaced by Si-phenyl groups is also used to reduce the Lewis acid–base interactions between the ceramic fillers, the polymer and the Li salt. Although nearly the same particle size and particle distribution are found for SiO2 and modified SiO2 in PEO, the two composite electrolyte systems exhibit remarkably different electrochemical transport properties. The difference can, therefore, be unambiguously attributed to the benefit of Lewis acid–base interactions.

Electrochemical transport properties of a cone-shaped nanopore: high and low electrical conductivity states depending on the sign of an applied electrical potential difference

Siwy and Fulinski have reported (Phys. Rev. Lett., 2002, 89, 198 103) that an alternating electrical current (frequency, e.g., ν = 0.01 s−1) passing through a single cone-shaped pore which is embedded in a polymer foil causes a net transport of potassium chloride across the pore. The foil separates two aqueous potassium chloride solutions having the same composition or different compositions. Two silver/silver chloride electrodes are used to pass an electric current across the pore. In the present study these findings are analysed in terms of the “model of the membrane with narrow pores”. This analysis leads to a qualitative explanation of the reported transport phenomenon distinctly different from that given by Siwy and Fulinski.

Charge transport effects in ferrocene–streptavidin multilayers immobilized on electrode surfaces

Streptavidin (SAv) has been modified by covalent coupling of ferrocene (Fc) electron-relay groups to lysine-residues of the protein backbone. Reagent ratios were varied to obtain conjugates with three to 16 Fc groups per SAv. Biotin was covalently attached to gold electrodes for the anchoring of the conjugate monolayers. A method was devised to produce in situ bisbiotin functionalities that efficiently cross-linked Fc 16SAv to form multilayer electrode coatings. The electrochemical charge transport properties of the coatings were examined by cyclic voltammetry. The characteristic current density i E measuring the rate of charge transport was 1 mA cm −2 for one monolayer of Fc 16SAv. It was found that the transport of electrochemical charge through the Fc-containing SAv system is a diffusion-like process, as evidenced by the proportionality of the peak current and the square root of sufficiently high scan rate, and the inverse dependence of i E on the number (thickness) of Fc 16SAv layers.

Effect of equivalent weight on electrochemical mass transport properties of oxygen in proton exchange membranes based on sulfonated α,β,β-trifluorostyrene (BAM®) and sulfonated styrene-(ethylene-butylene)-styrene triblock (DAIS-analytical) copolymers

Mass transport parameters and limiting current densities are determined for a series of sulfonated α,β,β-trifluorostyrene-co-substituted-α,β,β-trifluorostyrene (BAM®) (EW 407-735 g mol −1) and sulfonated styrene-(ethylene-butylene)-styrene copolymers (DAIS-Analytical) (EW 585–1062 g mol −1) proton exchange membranes using microelectrode techniques. These materials were investigated in an environment that mimics proton exchange membrane fuel cells. The oxygen diffusion coefficient increases with temperature, while its solubility decreases. All membranes exhibit a Henry's Law dependence for the limiting current of the oxygen reduction reaction with increasing oxygen pressure. The limiting current and the oxygen diffusion coefficient decreases with increasing equivalent weight, while the solubility of oxygen decreases due to the corresponding change in water content. These data are discussed in the context of previously published data on Nafion 117 and ethylenetetrafluoroethylene- g-polystyrene sulfonic acid membranes.

Influence of molybdenum on the conduction mechanism in passive films on iron–chromium alloys in sulphuric acid solution

This paper describes an extension of the mixed-conduction model to predict quantitatively the electrochemical behaviour and transport properties of anodic films on pure Cr, Fe–Cr alloys and Fe–Cr–Mo alloys in 1 M sulphuric acid solution. The anodic films on Fe–Cr–Mo alloys (12 and 25% Cr; 0, 5 and 10% Mo) were studied using rotating ring-disk voltammetry, impedance spectroscopy and resistance measurements. The addition of Mo to the Fe–Cr alloys was found to decrease the resistance of the film both in the passive and transpassive region. During the re-activation of the Fe–12%Cr– x%Mo alloys at negative potentials, soluble products were found to be released at a higher potential than during the re-activation of the Fe–12%Cr alloy. Re-activation proceeds to a lesser extent for the Fe–25%Cr alloy, and was not observed for the Fe–25%Cr– x%Mo alloys. The addition of Mo was also found to lead to a marked increase of the transpassive dissolution rate of the alloys. The impedance spectroscopic results indicated that the addition of Mo increases the rate of the interfacial generation of positive defects and especially annihilation of negative defects. The present extension of the mixed-conduction model for anodic passive films was found to describe quantitatively the resistance and impedance spectroscopic data for Fe–25%Cr and Fe–25%Cr–10%Mo alloy, as well as earlier data on pure Cr. The same kinetic model can be used to describe the behaviour of the films on all these materials. It is thus most likely that a Cr-oxide-based film is formed which determines the behaviour of the Fe–25%Cr and Fe–25%Cr–10%Mo alloys as well.

Stripping Voltammetry of Cu Overlayers Deposited on Self-Assembled Monolayers: Field Emission of Electrons through A Phenylene Ethynylene Oligomer

Copper overlayers were formed on electrodes coated with self-assembled monolayers (SAMs) of a molecular wire candidate, 1-thio-4-[4‘-[(4‘-thio)phenylethynyl]-1‘-ethynyl]-2‘,5‘-(diethyl)phenylbenzene (TTEB), by electrochemical reduction of copper ions and by physical vapor deposition. Anodic stripping voltammetry of copper was employed to study the electrochemical and electron transport properties of SAMs of these molecules. Electrochemical copper deposition revealed that SAMs of TTEB passivate the electrode to electrochemistry in a manner similar to alkanethiols. Migration of copper ions trapped within the TTEB SAM after copper oxidation was also observed. Reduction of the solvent prevented the application of a sufficient potential to deposit copper by conduction through the TTEB SAM, so evaporation of copper metal was employed to coat the entire electrode. Anodic stripping voltammetry first removed the metal from defect sites, leaving behind copper islands connected to the gold by TTEB molecules. At high...

Structure investigations of SOFC anode cermets. Part II: Electrochemical and mass transport properties

An approximate description of the SOFC cermet structure was performed on the basis of a combined optical and porosimetric structure analysis of the SOFC cermet anode and the results are described using the example of the SOFC substrate anode (anode with increased layer thickness). The electrode assembly consists of two layers. The electrochemically active layer of 70–90 μm corresponding the penetration depth of the electric field is located near the ZrO2 electrolyte. This layer thickness is also a function of porosity and pore radius distribution. The remaining electrode up to a layer thickness of about 2 mm basically acts only as a current and mass distributor. The corresponding diffusion overvoltage as a function of the structural properties was calculated.

Studies of electrochemical and mass transport properties of a thiolate/disulfide redox couple in polymer electrolytes

Electrochemical and mass transport properties of a thiolate/disulfide couple, formed by 5-mercapto-1-methyltetrazole lithium salt (LiT) and disulfide ( T 2) dissolved in liquid poly(ethylene glycol) 500 dimethyl ether, PEG(500), DME and soft methoxy-linked polyethylene oxide), PMEO, have been studied using a three-electrode microcell and a conventional three-electrode cell. Cyclic voltammetry showed that the electrochemical reversibility of the redox couple is poor in both solvents. The exchange current densities for the reduction and the oxidation reactions in PEG(500) DME-LiClO 4 are 0.24 μA cm −2 and 0.13μA cm −2, respectively. The diffusion coefficients of T − and T 2 in the same system are 7.88 × 10 −8 cm 2 s −1 and 6.01 × 10 −8 cm 2 s −1, respectively, at 23 °C, which are about 40 times higher than those measured in PMEO-LiClO 4. The diffusion coefficients of T − and T 2 in polymer electrolytes based on PMEO showed a VTF behaviour. The diffusion coefficient of T − increases (i) with decreasing LiT concentration and (ii) when T 2 species are present in the electrolyte.

Electrochemical quartz crystal microbalance: evidence for the adsorption of heteropoly and isopoly anions on gold electrodes

The electrochemical quartz crystal microbalance (EQCM) has been used to monitor electrochemical and mass transport properties during the cyclic voltammetry of selected isopoly and heteropoly anions. It is demonstrated that the oxidized form of these oxometalates (SiW12O4−40, P2W18O6−62 and H2W12O6−40) adsorb easily on gold electrodes, and this phenomenon is detected by the EQCM even at very low coverages. Conversely, in the same conditions, species associated with the first two redox couples of SiW12O4−40 and the first three couples of P2W18O6−62 are not adsorbed to an appreciable extent. The first redox couple of H2W12O6−40 is known to feature an ECE process. In this example, it appears that, in weakly acidic media (pH 3), the protonation of the reduced product associated with this first redox couple is fast enough to suppress any possible desorption and therefore only a global mass variation corresponding to a simple proton transfer during the ECE process is revealed.

Review of hybrid polymer electrolytes and rechargeable lithium batteries

The electrochemical and ion transport properties of heterogeneous electrolyte mixtures are reviewed. The review is restricted to lithium ion conducting electrolytes and to electrolytes containing at least one polymer component. Different electrolytetypes are compared, and lithium batteries based on the eletrolytes are described.