Determination of Ionic and Electronic Resistivities in Carbon/Polyelectrolyte Fuel-Cell Composite Electrodes

Saab, Andrew P.; Garzón, Fernando H.; Zawodzinski, Thomas A.

doi:10.1149/1.1516771

Cited by 79 publications

(65 citation statements)

References 15 publications

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“…There have been a few reports on the use of near-DC conditions to measure electronic and ionic conductivities in freestanding thin-film MIEC electrodes. [28][29][30][31][32] In some cases, the nature of the contact between the electrodes and the sample is controlled to restrict charge flow to only a certain type of charge carrier. These methods are similar to the Hebb-Wagner method that has long been used to study mixed electronic and ionic conduction in inorganic solids, e.g.…”

Section: -20mentioning

confidence: 99%

“…5,[33][34][35][36] This approach cannot be easily used on electrodes in an active fuel cell but it is nonetheless useful at the materials discovery stage because it allows for focused study of the variation in electronic and ionic conductivity contributions within electrodes in response to systematic variation of materials parameters and conditions. Such studies could be highly valuable in research aimed at creating new MIEC electrode materials.We report here on a simple but significant extension of some of this earlier work 28,29 for obtaining the separate contributions of electron and ion transport to the electrical conductivity of thin-film samples comprised of carbon black mixed with a polymer electrolyte. The method adapts a commercially available system for measuring inplane conductivity in thin films to allow for careful control of the nature of the contact between the sample and the current-carrying electrodes.…”

mentioning

confidence: 99%

“…We report here on a simple but significant extension of some of this earlier work 28,29 for obtaining the separate contributions of electron and ion transport to the electrical conductivity of thin-film samples comprised of carbon black mixed with a polymer electrolyte. The method adapts a commercially available system for measuring inplane conductivity in thin films to allow for careful control of the nature of the contact between the sample and the current-carrying electrodes.…”

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confidence: 99%

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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: -20mentioning

confidence: 99%

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confidence: 99%

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

Shetzline

Creager

2014

J. Electrochem. Soc.

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“…However, there is no detailed and quantitative study with experimental support on the effect of foreign cations on the ionic transport within the catalyst layer of a PEMFC due to the difficulty in conductivity measurement of the Nafion ionomer in a catalyst layer even in the absence of impurity. Up to the present, there is no experimentally measured proton conductivity for this layer that has been reported [Saab 2002]. The understanding of ionomer conductivity within the active layer is very important because the long-term durability and the performance of large-scale PEMFC operation, where commercial H 2 fuel and air streams contain some contaminant cations and material corrosion occurs, could be severely affected by proton starvation within the ionomer phase.…”

Section: Motivationmentioning

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Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

Goodwin¹,

Colón-Mercado²,

Hongsirikarn³

et al. 2011

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EXECUTIVE SUMMARYThe main objectives of this project were to investigate the effect of a series of potential impurities on fuel cell operation and on the particular components of the fuel cell MEA, to propose (where possible) mechanism(s) by which these impurities affected fuel cell performance, and to suggest strategies for minimizing these impurity effects. This project was carried out primarily at Clemson University and the Savannah River National Lab. Fuel cell investigations were done at SRNL while all investigations of the MEA components were carried out at Clemson. Meetings took place weekly at Clemson University and at SRNL with the respective project participants. Joint meetings between researchers at Clemson and SRNL took place quarterly, on average. In addition, frequent communications among project participants took place via e-mail and telephone discussions. On other occasions the researchers met with the technical staff of John Deere for discussions. At least one member of our team routinely participated in the DOE-Sponsored Joint Hydrogen Quality Task Force Meetings (usually conducted monthly).The nature and concentrations of impurities investigated and their impact on fuel cell performance and individual components are given in the table below. The negative effect on Pt/C was to decrease hydrogen surface coverage and hydrogen activation at fuel cell conditions. The negative effect on Nafion components was to decrease proton conductivity, primarily by replacing/reacting with the protons on the Bronsted acid sites of the Nafion.Even though already well known as fuel cell poisons, the effects of CO and NH 3 were studied in great detail early on in the project in order to develop methodology for evaluating poisoning effects in general, to help establish reproducibility of results among a number of laboratories in the U.S. investigating impurity effects, and to help establish lower limit standards for impurities during hydrogen production for fuel cell utilization.New methodologies developed included (1) a means to measure hydrogen surface concentration on the Pt catalyst (HDSAP) before and after exposure to impurities, (2) a way to predict conductivity of a Nafion membranes exposed to impurities using a characteristic acid catalyzed reaction (methanol esterification of acetic acid), and, more importantly, (3) application of the latter technique to predict conductivity on Nafion in the catalyst layer of the MEA. H 2 -D 2 exchange was found to be suitable for predicting hydrogen activation of Pt catalysts.Using a combination of standard catalyst characterization techniques, a structure sensitive catalytic reaction technique (cyclopropane hydrogenolysis), and reaction and transport modeling led to the finding that in the catalyst layer (essentially Nafion/Pt/C) the following best describes the structure. Pt is highly dispersed on the C support, but primarily in the meso-and macropores. The Nafion (ca. 30 wt%) resides primarily on the external surface of the C support where it blocks significant numbers ...

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“…Therefore, in situ measurements are needed to correlate changes in the electrode to its physical properties. For example, Shibuya et al 1 investigated the electronic conductivity of a composite cathode in a lithium battery, and Saab et al 2 the ionic and electronic conductivities of Nafion/ carbon composites. Shibuya et al 1 used an interdigitated array of electrodes to measure the electronic conductivity of Li x CoO 2 while simultaneously intercalating ͑or deintercalating͒ lithium into it.…”

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Theoretical Analysis for Obtaining Physical Properties of Composite Electrodes

Gomadam

Weidner

Zawodzinski

et al. 2003

J. Electrochem. Soc.

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A theoretical analysis is presented that allows in situ measurements of the physical properties of a composite electrode, namely, the electronic conductivity, the ionic conductivity, the exchange-current density, and the double-layer capacitance. Use is made of the current-voltage responses of the composite electrode to dc and ac polarizations under three different experimental configurations. This analysis allows the physical properties to be obtained even when the various resistances in the composite ͑e.g., ionic, electronic, and charge-transfer͒ are of comparable values.

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Determination of Ionic and Electronic Resistivities in Carbon/Polyelectrolyte Fuel-Cell Composite Electrodes

Cited by 79 publications

References 15 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

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

Theoretical Analysis for Obtaining Physical Properties of Composite Electrodes

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