Ionic conductivity measurements membranes

The physical and electrochemical properties of a new class of hthium ion conducting polymer electrolytes formed by dispersing nanosized C CPO ) in the poly (vinyhdene fluoride-hexafluoro propylene) (PVDF-HFP) - LiClO complexes have been reported. The prepared membranes were subjected to XRD, SEM, TG-DTA, and FT-IR analysis. Ionic conductivity measurements have been made as a function of temperature and hthium salt concentrations. The polymeric film with a ratio of PVDF-HFP Ca3(PO )2 LiC10 75 15 10 offered maximum ionic conductivity. The interfacial property of Li/NCPE was also analyzed. The interaction that exists between the polymer and lithium salt species has been confirmed by FT-IR analysis. 

Alternatively, CNT-polymer composites have been utilized as polymer electrolyte membranes in fuel cell devices (PEMFCs) [111]. Sulfonic acid-functionalized CNTs were blended with Nafion polymer so that the proton transport capability of the polymer matrix could be enhanced appreciably. Ionic conductivity measurements of Nafion and CNT-Nafion membranes revealed almost one order of magnitude higher conductivity for the composite than that for neat matrix. 

Without absorbing water, these PEMs tend to be rather rigid and are poor ionic conductors. The ionic conductivity would dramatically increase with water content [78]. Therefore, ionic conductivity tests are mostly conducted in water or in water vapor with adequate related humidity. Two types of ionic conductivity for PEMs were used in-plane and through-plane conductivities. The former represents the conductivity along the membrane surface direction, and the latter refers to the conductivity across the membrane thickness direction. In addition, there are two methods for conductivity measurement two-point probe electrode and four-point probe electrode. The latter method is more accurate but the former uses a simpler device. Therefore, comparison of ionic conductivities between membranes must be of the same type and measured through the same method. The aforementioned conductivity measurements are suitable for both proton conductivity and anion conductivity. Proton conductivity (o) is calculated by the following equation [79-82] ... 

Figure 13. Schematic diagram of the measurement of the ionic conductivity of a conducting polymer membrane as a function of oxidation state (potential), (a) Pt electrodes (b) potentiostat (c) gold minigrid (d) polymer film (e) electrolyte solution (0 dc or ac resistance measurement.133 (Reprinted with permission from J. Am Chem Soc. 104, 6139-6140, 1982. Copyright 1982, American Chemical Society.)...

A number of methods have been used for determining Kg values cation selective electrodes, pH-metric methods, conductimetry, calorimetry, temperature-jump relaxation measurements, membrane conductance measurements, nuclear magnetic resonance, optical rotatory dispersion. The results listed in Tables 7—10 have been obtained by various methods and at different ionic strengths so they may not always be strictly comparable. However, the corrections are probably small and the experimental accuracy is generally the same or very similar within a certain ligand type. 

The fluoride electrode is a typical example of an ion selective electrode. Its sensitive element is a crystal of lanthanum trifluoride that allows fluorine atoms to migrate into the network formed by lanthanum atoms (Fig. 18.3). Other electrodes use a mineral membrane obtained as agglomerates of crystalline powders (for measurement of Cl-, Br-, I , Pb++, Ag+ and CN ). Generally, the internal electrolyte can be eliminated (by dry contact). However, it is preferable to insert a polymer layer with a mixed-type conductivity to ensure the passage of electrons from the ionic conductivity membrane to the electronic conductivity electrode (Fig. 18.3). 

Ionic conductivity of purified Na+ channels reincorporated into phospholipid bilayers, (a) The current through a single channel is measured as a function of time. Downward deflections of the traces indicate openings of the channel (increased current of Na+ across the membrane). The numbers on the right indicate the electric potential difference across the membrane (Atji). When Ai// is made less negative, the channel opens more frequently and stays open longer. 

Figure 5.9. AC impedance spectra of Nafion 115 membrane obtained by the two-probe cell method with different probe distances, at room temperature and under fully hydrated conditions [9], (Reproduced by permission of ECS—The Electrochemical Society, from Xie Z, Song C, Andreaus B, Navessin T, Shi Z, Zhang J, Holdcroft S. Discrepancies in the measurement of ionic conductivity of PEMs using two- and four-probe AC impedance spectroscopy.)...

Figure 5.14. Schematic of the four-electrode glass cell used for conductivity measurements on a circular sample of the membrane, using a steady-state linear sweep galvanodynamic technique [10], (Reproduced by permission of ECS—The Electrochemical Society, from Slade S, Campbell SA, Ralph TR, Walsh FC. Ionic conductivity of an extruded Nafion 1100 EW series of membranes.)...

The authors state that while the above definition is used widely, other authors have defined tortuosity as 1/T, T, and l/T as these forms are frequently encountered in expressions for ionic conductivity and mobility through tortuous membranes. Experimental measurement of liquid membrane support tortuosity is described by Bateman et al. 

The channels, which had catalyzed electrodes on the surfaces, were covered with Nafion 112 (thickness 50 pm, equivalent weight 1,100 gmoF, ionic conductivity 0.083 S cm" ) to provide ionic conductivity between the anode and the cathode. The Nafion membrane was pressed with a glass plate to avoid solution leakage (Fig. 3.4a). Voltage-current measurements were performed at room temperature with a mass flow control system of fuel and oxidant as shown in Fig. 3.4b. The fuel and oxidant solutions were supplied to the electrodes with the micro-syringe pumps from the outlet of each channel. The flow rate of both the fuel and oxidant solutions was 80 pL miu". Composition of the fuel solution was 2M methanol solution... 

Fig. U Electrochemical scheme of measuring the ionic conductivity of perfluorlnated Ionomer membranes.

In their classic series of papers, Hodgkin and Huxley gave a quantitative description of the unique electrical behavior of the giant nerve fibers (axons) of squid. This behavior is described in terms of permeability of the surface membrane (measured as conductance per unit area of membrane) to different ion species, particularly Na+ and K+. The current carried by an ion species through the membrane is then calculated from the product of conductance and driving force on them (transmembrane voltage, V, minus ion equilibrium potential). The specific ionic conductances have several unique properties which challenge explanation at the molecular level ... 

Bozler and Cole (1935) measured the electrical impedance of frog sartorius muscle from 1.1 kHz to 1.1 MHz. Measurements were first done approximately 2 h after dissection. The tissue was then stimulated to induce contraction, and the tissue was measured again, approximately 3 h after dissection. They found a minor arc of a circle when the data were plotted in the complex impedance plane. Between the relaxed and contracted state, Rq was found to increase by 75% whereas Roo increased only 2%. As usual, Rq and Ra> denote the resistances measured at very low and very high frequency, respectively. The significant increase in Rq was interpreted as a reduced ionic conduction through the cell membranes. 

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