The application of electroanalytical methods to the analysis of phase transitions during intercalation of ions into electrodes

Mechanisms of first-order phase transition induced by electrochemical intercalation of Li ions into composite graphite electrode are studied both theoretically, in the framework of lattice gas models, and experimentally, by a combination of electroanalytical techniques, such as cyclic voltammetry, potentiostatic intermittent titration (PITT), galvanostatic intermittent titration (GITT), and electrochemical impedance spectroscopy (EIS). From the analysis of the mismatch between the accessible phase-transition rate constants and the characteristic time windows for various electroanalytical methods, we conclude that only a combined application of these techniques provides sufficient, self-consistent information on the mechanisms of phase transitions in graphite electrodes. The advantages and disadvantages in using these techniques are discussed. PITT with a small potential step is the most appropriate tool for measuring the entire sequence of rate-determining steps of phase transitions as a function of time. The latter technique can be conveniently used for quantitative analysis of slow nucleation and the growth of new phases in the bulk of the old one, followed by the coalescence of nuclei and the formation of phase boundaries between the coexisting phases. The movement of this boundary into the electrode’s bulk has been properly modeled in terms of two alternative models. “Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006.”     

Comparison of methods for the determination of diffusion coefficients of polymers in dilute solutions: The influence of polydispersity

A comparison between various methods to determine diffusion coefficients of polymers in dilute solutions has been made. It is shown that Taylor dispersion analysis (TDA), dynamic light scattering (DLS), hydrodynamic chromatography (HDC), and size exclusion chromatography (SEC) can all be used to accurately determine diffusion coefficients when the polymer samples have low polydispersities. By the analysis of a series of practically representative styrene acrylonitrile copolymer (SAN) samples, it is shown that polydispersity of the samples and the presence of low‐molecular‐mass material cause considerable differences between the methods. It was found that TDA is mostly disturbed by the presence of low‐molecular‐mass material, whereas DLS is more sensitive to the polydispersity of the polymer. With broad samples, DLS gives the Z‐average diffusion coefficient. SEC can be used to obtain a diffusion coefficient distribution as well as an average diffusion coefficient of a polydisperse sample. Although, the same was expected for HDC, it was found that this method could only be successfully used for polymer samples having low polydispersities. Deviations between SEC, HDC, and TDA found for narrow samples were not related to the chemical composition of the samples. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 593–603, 1999     

Electrochemical time of flight method for determination of diffusion coefficients of glucose in solutions and gels

The diffusion coefficient of glucose in different media is an important parameter in life sciences, as well as in biotechnology and microbiology. In this work a simple, fast method is proposed that is based on the electrochemical time of flight principle. In most of the earlier time of flight experiments performed, a constant flight distance was applied. In the present work a scanning electrochemical microscope (SECM) was applied as a measuring tool. With use of the SECM, the flying distance could be changed with high precision, making measurements with several flight distances more accurate and reliable values could be obtained for solutions as well as for gels. The conventional voltammetric methods are not applicable for glucose detection. In our work electrocatalytic copper oxide coated copper microelectrodes and micro-sized amperometric enzyme sensors were used as detectors, while microdroplet-ejecting pneumatically driven micropipettes were used as a source. Figure Experimental set up for SCEM-TOF diffusion coefficient measurements Presented at the 9th International Symposium on Instrumental Analysis, Pécs, Hungary, 29 July-2 August 2008     

A systematic determination of diffusion coefficients of trace elements in open and restricted diffusive layers used by the diffusive gradients in a thin film technique

A systematic comparison of the diffusion coefficients of cations (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and oxyanions (Al, As, Mo, Sb, V, W) in open (ODL) and restricted (RDL) diffusive layers used by the DGT technique was undertaken. Diffusion coefficients were measured using both the diffusion cell (D_cell) method at pH 4.00 and the DGT time-series (D_DGT) method at pH 4.01 and 7.04 (pH 8.30 was used instead of 7.04 for Al) using the Chelex-Metsorb mixed binding layer. The performance of Chelex-Metsorb as a new DGT binding layer for Al uptake was also evaluated for the first time. Reasonable agreement was observed between D_cell and D_DGT measurements for both ODL and RDL, except for V and W. The ratios of D_cell/D_DGT for V of 0.44 and 0.39, and for W of 0.66 and 0.63 with ODL and RDL respectively, were much lower due to the formation of a high proportion of polyoxometalate species at the higher concentrations required with the D_cell measurements. This is the first time that D values have been reported for several oxyanions using RDL. Except for Al at pH 8.30 with ODL, all D_DGT measurements were retarded relative to diffusion coefficients in water (D_W) for both diffusive hydrogels. Diffusion in RDL was further retarded compared with ODL, for all elements (0.66–0.78) with both methods. However, the degree of retardation observed changed for cations and anions at each pH. At pH 7.04 cations had a slightly higher D_DGT and oxyanions had a slightly lower D_DGT than at pH 4.01 for both ODL and RDL. It is proposed that this is due to partial formation of acrylic acid functional groups (pK_a ≈4.5), which would be fully deprotonated at pH 7.04 (negative) and mostly protonated at pH 4.01 (neutral). As Al changes from being cationic at pH 4.01 to anionic at pH 8.30 the results were more complex.     

Electrochemical determination of standard thermal diffusion characteristics for chlorides of hydrogen and potassium in water-ethanol solutions

Initial and steady-state temperature coefficients of the voltage generated by thermogalvanic cells comprising silver chloride and quinhydrone electrodes in the systems HCl-H₂O-C₂H₅OH and KCl-H₂O-C₂H₅OH are determined. Standard thermal diffusion Soret coefficients, the entropy of thermal diffusion transport of electrolytes, and the entropy of mobile ions H⁺, K⁺, and Cl^? are calculated for 298 K. The effect the nature of ions and the solvent composition exert on the obtained thermal diffusion transport characteristics is considered in terms of the De Bethune theory.     

Simple technique for the simultaneous determination of solvent diffusion coefficient in polymer by Quantum Resistive Sensors and FT‐IR spectroscopy

A simple, quick and novel method for the determination of diffusion properties through polymer films, based on Quantum Resistive Sensors made of Conductive Polymer nanoComposites is presented. The integral time lag method is employed for the calculation of diffusion coefficient, and the results are compared simultaneously with that of Fourier transform infrared spectroscopy and sorption method. Two model polymers, a semi‐crystalline poly(lactic acid) and an amorphous poly(isobutylene‐co‐isoprene), are used to validate the study. A good correlation is established between the diffusion coefficient values derived from all techniques demonstrating the interest of such reliable, simple and cheap nanosensors for the quick determination (several minutes) of diffusion properties in polymer films. Our first results suggest that this technique is meaningful for the determination of barrier properties in nanocomposite membranes filled with platelets of graphene or clay. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of diffusion coefficients for sulfide ions in solid electrolytes on the basis of BaSm<Subscript>2</Subscript>S<Subscript>4</Subscript> and CaGd<Subscript>2</Subscript>S<Subscript>4</Subscript>

Coefficients of self-diffusion and coefficients of diffusion of the sulfur ion in solid electrolytes BaSm₂S₄ and CaGd₂S₄ are determined with recourse to methods of conductimetry and potentiostatic chronoamperometry. A vacancy mechanism for the defect formation in solid solutions on the basis of barium thiosamarate and calcium thiogadolynate is proposed.     

Measurements of binary diffusion coefficients and retention factors for dibenzo-24-crown-8 and 15-crown-5 in supercritical carbon dioxide by chromatographic impulse response technique

Binary diffusion coefficients D₁₂ and retention factors k for dibenzo-24-crown-8 and 15-crown-5 ethers at 308.18 and 313.20 K, and vitamin K₁ at 313.20 K were measured in supercritical carbon dioxide by the chromatographic impulse response technique, and the effects of molecular shapes on the D₁₂ values were studied. At 313.2 K and 11.0 MPa the D₁₂ value of 15-crown-5 was higher than that predicted from the D₁₂ correlation with molecular weight MW over the range from 32 of methanol to 1138 of trinervonin reported in our previous studies, while the D₁₂ value of dibenzo-24-crown-8, disk shape molecule with MW = 448.5, was almost in agreement with that of vitamin K₁, long chain molecule with MW = 450.7, and with those predicted from the correlation.     

Viscosity of aqueous NH4Cl and tracer diffusion coefficients of ions,water and non-electrolytes in aqueous NH4Cl,KI, and MgCl2 at 25°C

Viscosities for aqueous NH₄Cl and tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, HTO, and CH₃OH, acetone and dimethylformamide (all¹⁴C-labelled) in NH₄Cl supporting electrolyte are reported for 25°, together with tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, and¹⁴CH₃OH in 1M KI, and for¹⁴CH₃OH in 1M MgCl₂. The diffusion coefficient of HTO in NH₄Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5 M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH₃OH, acetone and dimethylformamide in NH₄Cl solutions. Onsager limiting law behavior is approached by Cl^– at NH₄Cl concentrations in the 0.05–0.1M region but at much lower concentrations by Na⁺.