The characterization of porous electrodes by impedance measurements

Candy, Jean‐Pierre; Fouilloux, P.; Keddam, M.; Takenouti, H.

doi:10.1016/0013-4686(81)85072-4

Cited by 164 publications

(98 citation statements)

References 4 publications

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“…This observation supports the conclusion that the interfacial impedance including the photoablated PET microchannel should not be represented as a pure capacitance. To take into account this characteristic, the De Levie model [27] for rough surface was used and adapted by different authors [28][29][30] in order to determine impedance in rough or porous surfaces. In our case, this model could be also adapted for a microstructured surface.…”

Section: Eis Measurements In Microchannel Filled With Nacl Solutionmentioning

confidence: 99%

Polymer microchip impedance spectroscopy through two parallel planar embedded microelectrodes: Understanding the impedance contribution of the surrounding polymer on the measurement accuracy

Kechadi

Gamby

Chaal

et al. 2013

Electrochimica Acta

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a b s t r a c tThe present work describes a new methodology for contact free impedance of a solution in a polymer microchip taking into account the role played by the surrounding polymer on the impedance accuracy. Measurements were carried out using a photoablated polyethylene terephthalate (PET) microchannel above two embedded microband electrodes. The impedance diagrams exhibit a loop from high frequencies to medium frequencies (1 MHz-100 Hz) and a capacitive behavior at low frequencies (100-1 Hz). The impedance diagrams were corrected by eliminating from the global microchip response the contribution of the impedance of the PET layer between the two microband electrodes. This operation enables a clear observation of the impedance in the microchannel solution, including the bulk solution contribution and the interfacial capacitance related to the surface roughness of the photoablated microchannel. Models for the impedance of solutions of varying conductivity showed that the capacitance of the polymer-solution interface can be modeled by a constant phase element (CPE) with an exponent of 0.5. The loop diameter was found to be proportional to the microchannel resistivity, allowing a cell constant around 4.93 × 10 5 m −1 in contactless microelectrodes configuration.

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Section: Eis Measurements In Microchannel Filled With Nacl Solutionmentioning

confidence: 99%

Polymer microchip impedance spectroscopy through two parallel planar embedded microelectrodes: Understanding the impedance contribution of the surrounding polymer on the measurement accuracy

Kechadi

Gamby

Chaal

et al. 2013

Electrochimica Acta

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“…1a͒. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] The overall impedance has been derived by de Levie as Eq. 1, assuming that the electrode resistance is negligible as compared to the electrolyte resistance in pores.…”

Section: Theorymentioning

confidence: 99%

Complex Capacitance Analysis on Leakage Current Appearing in Electric Double-layer Capacitor Carbon Electrode

Jang

Yoon

et al. 2005

J. Electrochem. Soc.

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Complex capacitance analysis was done on the porous carbon electrode-electrolyte interface, where a minor leakage current is involved in addition to the dominant capacitor charging current. Based on the transmission line model, imaginary capacitance profiles ͑C im vs. log f͒ were theoretically derived for a cylindrical pore and multiple pore systems of nonuniform pore geometry. The parallel RC circuit was assumed for the interfacial impedance, where R is the charge-transfer resistance for leakage current and C the double-layer capacitance. The theoretical derivation illustrated that the resistive tail relevant to the leakage current appears in addition to the capacitive peak, which was in accordance with the experimental data taken on the porous carbon electrode. The electric double-layer capacitor ͑EDLC͒ parameters such as the extent of leakage current, total capacitance, and rate capability were visually estimated from the imaginary capacitance profiles. The more quantitative EDLC parameters were obtained by a nonlinear fitting to the experimental data. Electric double-layer capacitor ͑EDLC͒ utilizes the double layer formed at the electrode-electrolyte interface, where electric charges are stored on the electrode surface and ions of counter charge are arranged in the electrolyte side. The most demanding feature for EDLC electrodes is the ideally polarized behavior over a wide potential range. The practical EDLC electrodes, however, suffer from a self-discharge at the charged state that is caused by leakage currents. [1][2][3][4][5] This nonideally polarized behavior should thus be minimized to improve the charge-discharge efficiency and reliability of commercial cells.The leakage current appearing in EDLC electrodes can be analyzed using ac impedance spectroscopy. When impedance data are analyzed using the conventional Nyquist plot, the vertical line in the low-frequency region that is observed for ideally polarized electrodes becomes inclined with an increase in the leakage current. [6][7][8] The extent of leakage current can thus be estimated from the degree of inclination. The problem here, however, is that the inclination is also observed even in ideally polarized electrodes when they have a nonuniform pore geometry that is common in most practical porous EDLC electrodes. [9][10][11][12] In theory, the differentiation between the leakage current and nonuniform pore geometry for the cause of inclination is possible when the measurement is made at very low frequencies. In the extremely low-frequency region, ideally polarized electrodes with nonuniform pore geometry give a vertical line on the Nyquist plot, whereas the leakage current is visualized as a semicircle whose diameter reflects the charge-transfer resistance for leakage reaction. In practice, however, it is difficult to obtain data at such a low frequency due to an instrumental limitation and extremely long measuring time.In this work, the complex capacitance analysis is done on the leakage current involved in porous carbon electrode. From the imagi...

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“…Key requirements to maintain high-frequency operation are: 1) the charge storage material must be connected ohmically to the graphene nanosheets with minimal electronic resistance, and 2) the material must be added in such a way that it does not create significant distributed charge storage behavior, which can arise from rough surfaces 19 and densely packed particulate. 21 Examples of possible charge storage material include carbon black to enhance electric double layer charge storage, or materials like polythiophene, ruthenium oxide, and manganese oxide that provide pseudocapacitance charge storage.Cabot SC3 carbon black was used in this study because of its good electronic conductivity, high surface area (∼1800 m 2 /g), and its demonstrated performance as an EDLC charge storage material. …”

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confidence: 99%

Vertically-Oriented Graphene Electric Double Layer Capacitor Designs

Miller

Outlaw

2015

J. Electrochem. Soc.

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High-voltage electric double layer capacitors (EDLCs) capable of efficient AC line-filtering have been developed. They were fabricated with vertically-oriented graphene nanosheet (VOGN) electrodes using a planar design. Two approaches were examined to series connect EDLC cells and thus achieve high-voltage operation. Electrical performance of VOGN electric double layer capacitors fabricated with an ionic liquid electrolyte was measured at temperatures up to 125 • C. Volume comparisons are made between VOGN electric double layer capacitors and aluminum electrolytic capacitors. A practical design is presented that provides the VOGN electric double layer capacitor with more than an order-of-magnitude higher ripple-current filtering performance Efficient AC line-filtering (120 Hz) by an electric double layer capacitor (EDLC) was first demonstrated in 2010 using electrodes of vertically-oriented graphene (VOGN) grown directly on nickel.1 This electrode material and its structure ( Figure 1) reduce series resistance to an absolute minimum value and effectively eliminate distributed charge storage, i.e. porous electrode behavior with its corresponding transmission-line-like electrical response. In brief, EDLC electrodes are made by growing the VOGN on bare nickel current collectors using radio frequency plasma enhanced chemical vapor deposition of CH 4 /H 2 or C 2 H 2 /H 2 feed gases.2,3 Growth temperature is typically in the 550 to 850• C range. No catalytic seed material is required or added to the nickel surface. Growth proceeds by Volmer-Weber island impingement, 4 which yields an upturned structure at carbon island boundaries. There is significant carbon dissolution into the nickel during growth that helps ensure low-resistance ohmic connection between the high-conductivity graphene sheets and the metal current collector. Typical characteristic VOGN spacing is ∼200 nm and heights ∼1 μm, a void length-to-width ratio that thwarts porous electrode behavior as found with activated-carbon. 5Generally the Raman D band to G band intensity ratio decreases with growth time indicating that crystalline order of the VOGN increases with nanosheet height, which increases approximately linearly with time at growth rates of 70 nm/minute using CH 4 and 190 nm/minute using C 2 H 2 .6 Electrode capacitance at 120 Hz typically is in the 200 to 300 μF/cm 2 range, depending on VOGN growth conditions and growth time. The frequency response reported for EDLCs made using other external-surface-area nanomaterials is generally below that demonstrated by VOGN grown on nickel because of higher series resistance and/or distributed charge storage behavior. 7-12State of the art commercial EDLCs, which use internal-surface-area activated carbon electrode materials, typically have a -45• phase angle at ∼0.2 Hz and show inductive behavior (positive phase angle) at 120 Hz, rendering them totally useless for AC line filtering. 13 EDLC DesignsA conventional EDLC "sandwich" design, as depicted in Figure 2, is poorly suited for capacitors made using V...

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The characterization of porous electrodes by impedance measurements

Cited by 164 publications

References 4 publications

Polymer microchip impedance spectroscopy through two parallel planar embedded microelectrodes: Understanding the impedance contribution of the surrounding polymer on the measurement accuracy

Polymer microchip impedance spectroscopy through two parallel planar embedded microelectrodes: Understanding the impedance contribution of the surrounding polymer on the measurement accuracy

Complex Capacitance Analysis on Leakage Current Appearing in Electric Double-layer Capacitor Carbon Electrode

Vertically-Oriented Graphene Electric Double Layer Capacitor Designs

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