Density and Solubility of Nafion:  Recast, Annealed, and Commercial Films

Zook, Lois Anne; Leddy, Johna

doi:10.1021/ac960604e

Cited by 171 publications

(142 citation statements)

References 21 publications

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“…Estimates of sample density obtained in this way are provided in Table I. Density estimates for commercially-obtained membranes of Nafion and PVDF (first two entries in Table I) agree with literature values (1.76-1.78 g/cm 3 for PVDF and 1.8-2.0 g/cm 3 for Nafion, depending upon source and pretreatment) 43 to within ten percent, however the measured densities for solvent-cast films of PVDF and Nafion (second two entries in Table I) are lower, and those for both of the composite samples (last two entries) are much lower, well below 1.0 g/cm 3 . Calculated densities listed in Table I for the composite samples are obtained assuming no free volume and an amorphous carbon density of 2.0 g cm −3 .…”

Section: Resultssupporting

confidence: 78%

Quantifying Electronic and Ionic Conductivity Contributions in Carbon/Polyelectrolyte Composite Thin Films

Shetzline

Creager

2014

J. Electrochem. Soc.

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A method for independently obtaining electronic and ionic contributions to electrical conductivity in thin-film samples comprised of carbon black (CB) mixed with polymer electrolyte is reported. The method relies upon careful control of the nature of the contact between the sample and the current-carrying electrodes. Electronic conductivities are derived from currents obtained using electronically-conductive glassy carbon electrodes to contact the sample, whereas ionic conductivities are derived from currents obtained using ionically-conductive Nafion electrodes to contact the sample. Conditions under which the measured currents are free from interference from redox reactions at the electrodes and capacitive charging at electrode-electrolyte interfaces are discussed. Electrical conduction was studied in a series of composite carbon black/polymer samples under conditions of fixed temperature and variable relative humidity (RH). For samples containing 10-20 weight percent carbon black dispersed in Nafion, electronic conductivity was higher than ionic conductivity at all RH values tested (25-100% RH). Ionic conductivity increased with increasing RH in a manner consistent with expectation from prior studies on Nafion membranes, whereas electronic conductivity decreased with increasing RH due to water swelling and weakened electrical contacts among carbon particles in the network. Electrical conduction in materials may arise from motion in an electric field of electrons, ions, or both. For many materials the charge carrier identity is implicit; e.g. for metals and semimetals such as carbon, charge is understood to be carried by mobile electrons, whereas for electrolyte materials such as salts dissolved in solvents and most polymer electrolytes, charge is understood to be carried by mobile ions.1,2 Some materials have the very interesting property that they may transport charge via both ions and electrons; such materials are referred to as mixed ionic electronic conductors (MIECs).3-5 MIEC materials are critically important in many electrochemical technologies, for example in battery electrodes, 6-13 fuel-cell electrodes, [14][15][16] and in certain types of membrane reactor. 17-20A simple measurement of electrical resistance/conductance on a bulk sample, for example from the current obtained upon application of a potential difference between two points on the sample using current-carrying electrodes, can provide values for resistivity/conductivity but it does not provide information on the nature of the charge carrier(s). Four-point-probe (e.g. van der Pauw) measurements are useful for eliminating the influence of contact resistance at the current-carrying electrodes on the measured resistance but such measurements still do not distinguish whether charge is carried by electrons, ions, or both. For some special situations, e.g. doped semiconductors, information about charge-carrier identity may be obtained from the behavior of the sample in response to an external perturbation. For example, in the case of Hall-effect ...

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Section: Resultssupporting

confidence: 78%

Quantifying Electronic and Ionic Conductivity Contributions in Carbon/Polyelectrolyte Composite Thin Films

Shetzline

Creager

2014

J. Electrochem. Soc.

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“…However, the described Nafion ® pre-coat method displays both anionic and cationic rejection characteristics while facilitating the diffusion of gaseous molecules such as NO and O2 to the electrode surface. The extremely selective nature of this film can be attributed to the annealing procedure which reduces the permeability of the film by increasing the crystallinity of the film [36,37]. Similar to the Pt-PPD electrode, the maximum current recorded at 1000 μM AA on day 3 (260 ± 211 pA, n = 4), day 7 (592 ± 328 pA, n = 4), day 14 (1254 ± 902 pA, n = 4) and day 28 (1598 ± 1099 pA, n = 4) demonstrated no significant difference (p > 0.05) from day 1(131 ± 29 pA, n = 4), though, day 56 (2707 ± 1031 pA, n = 4) did reveal a significant difference (p < 0.05).…”

Section: Shelf-life Studies-effect Of Repeated Aa Calibrationsmentioning

confidence: 99%

Ascorbic Acid Rejection Characteristics of Modified Platinum Electrodes: A Shelf Life Investigation

Wynne

Finnerty

2015

Chemosensors

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Ascorbic acid (AA) is the principle interferent present in brain extracellular fluid that can inhibit the ability of electrochemical sensors to selectively detect a particular analyte of interest. Considerable efforts have been made in recent times to develop highly selective membrane coatings to counteract the drawbacks associated with AA interference during in vivo monitoring. The primary objective of the work described within was to investigate the long term effect of storing such selective membranes, i.e., Nafion ® andPoly-o-phenylenediamine (PPD) under different conditions and how exposing them to repeated calibration protocols compromises the membranes ability to reject AA. Four different modified platinum (Pt) electrodes, Pt-PPD, Pt-Nafion ® (5/2), Pt-Nafion ® (1/2)-PPD, and Pt-Nafion ® (2/1)-PPD, stored at 4 °C demonstrated deterioration of the polymers integrity when exposed to repeated calibrations. On the contrary, exposing the same four electrode types to single calibrations confirmed excellent retention of AA rejection characteristics. Pt-PPD electrodes were then exposed to varying storage conditions and calibrated against AA on day 1, day 56 and day 168. Storing the Pt-PPD electrodes at 4 °C/N2 saturated glass container demonstrated retention of AA rejection characteristics after day 168. These results have clearly elucidated the optimum storage conditions for Pt-Nafion ® and Pt-PPD modified electrodes.

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“…8,9,29 In biphasic Nafion with aqueous and fluorocarbon phases, volume fractions of fluorocarbon v C F and hydrated domains v aq are calculated from density of fluorocarbon, estimated from Teflon d C F = 2.15 g/cm 3 , and density of water, 14 Sulfonate is determined by fully protonating weighed Nafion in strong acid; rinsing unbound proton; flushing all bound H + by exchange with excess Na + ; and titrating the H + with sodium hydroxide to a phenolphthalein end point. Because this is an aqueous acid base titration, measured sulfonate is specific to the aqueous (hydrated) domain.…”

mentioning

confidence: 99%

Electron Hopping of Tris (2,2^′-bipyridyl) Transition Metal Complexes M(bpy)^2/3₃in Nafion

Gellett

Knoche

Rathuwadu

et al. 2016

J. Electrochem. Soc.

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Voltammetric currents of transition metal complexes in films on electrodes increase with electron self exchange (hopping) rate k11. In films, diffusion coefficients Df∝k11c*f, where k11 sets frequency of electron hopping attempts and c*f film concentration sets distance between probes. Cyclic voltammetry of Nafion films on electrodes for six probes, tris(2,2′-bipyridyl) complexes, M(bpy)z +3 where Mz + is Ru2+, Os2+, Fe2+, Cr3+, Co3+, and Co2+, demonstrates Df varies linearly with kH2O11, literature k11 measured in water. From density of Ru(bpy)2 +3 exchanged Nafion 1.95 g/cm3 and nominal equivalent weight 1100, geometry establishes volume limited, z-independent c*f for all M(bpy)z +3. For concentrations of Ru(bpy)2 +3 in HNO3 where either Ru(bpy)2 +3: HNO3 ratio is fixed or Ru(bpy)2 +3 is 1 mM and HNO3 varies, c*f is statistically invariant. Based on aqueous titrations and dielectric constant sufficient to support ions, electron hopping is confined to hydrated domains of Nafion. From c*f, k11 in Nafion kNaf11 is estimated as k11Naf=0.010k11H2O, consistent with higher ion concentration in Nafion. Measured Df is 2 × 10− 9 cm2/s for Ru(bpy)2 +3 and Os(bpy)2 +3; 1 × 10− 10 cm2/s for Fe(bpy)2 +3 and Cr(bpy)3 +3; and 1.5 × 10− 12 and 5 × 10− 12 cm2/s for Co(bpy)2 +3 and Co(bpy)3 +3. For physical diffusion Dp ≲ 10− 12 cm2/s. A self consistent view of M(bpy)z +3 self exchange in Nafion is outlined. For Os(bpy)2/33, kH2O11 ≈ 4.5 × 108/Ms.

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Density and Solubility of Nafion: Recast, Annealed, and Commercial Films

Cited by 171 publications

References 21 publications

Quantifying Electronic and Ionic Conductivity Contributions in Carbon/Polyelectrolyte Composite Thin Films

Quantifying Electronic and Ionic Conductivity Contributions in Carbon/Polyelectrolyte Composite Thin Films

Ascorbic Acid Rejection Characteristics of Modified Platinum Electrodes: A Shelf Life Investigation

Electron Hopping of Tris (2,2^′-bipyridyl) Transition Metal Complexes M(bpy)^2/3₃in Nafion

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Density and Solubility of Nafion: Recast, Annealed, and Commercial Films

Cited by 171 publications

References 21 publications

Quantifying Electronic and Ionic Conductivity Contributions in Carbon/Polyelectrolyte Composite Thin Films

Quantifying Electronic and Ionic Conductivity Contributions in Carbon/Polyelectrolyte Composite Thin Films

Ascorbic Acid Rejection Characteristics of Modified Platinum Electrodes: A Shelf Life Investigation

Electron Hopping of Tris (2,2′-bipyridyl) Transition Metal Complexes M(bpy)2/33in Nafion

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Product

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Electron Hopping of Tris (2,2^′-bipyridyl) Transition Metal Complexes M(bpy)^2/3₃in Nafion