Double Layer Capacitance and Charging Rate of Ultramicroporous Carbon Electrodes

Koresh, Jacob E.; Soffer, Abraham

doi:10.1149/1.2133657

Cited by 115 publications

(70 citation statements)

References 12 publications

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“…Several experimental and theoretical studies suggested that ionic conductivity in pores is lower than bulk ion conductivity because of electrostatic interaction between ions and pore surface. 24,25 In this particular system, it is very possible that the pore surface is negatively charged upon a negative polarization and has a stronger attraction for the quaternary ammonium ions. This would explain why the ionic conductivity and rate capability is lower at 1.0 V than at 3.0 V ͑vs.…”

Section: Resultsmentioning

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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Section: Resultsmentioning

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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“…The amount of CO-evolving groups does not change substantially, whereas the groups responsible for the CO 2 evolution significantly increased (from 0.2 to 0.8 mmol/g). When moderate oxidation takes place, the morphology of the carbon material does not change significantly, although some oxygen functional groups can be created at the surface of the material (i.e., hydroxyl groups) that could lead to an improvement in wettability [32] and/or could lead to enhanced specific capacitance values [33]. However, a strong oxidation can lead to deeper structural modifications that can cause the degradation of the carbon material (i.e.…”

Section: -Results and Discussionmentioning

confidence: 99%

Long-term cycling of carbon-based supercapacitors in aqueous media

Ruíz

Santamarı́a

Granda

et al. 2009

Electrochimica Acta

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Abstract.-The behaviour of mesophase-derived electrodes on long-duration cycling conditions was studied in 1M sulfuric acid and 6M potassium hydroxide. Variation in the specific capacitance values with the number of cycles shows a good cycling life performance in acidic media but very poor in an alkaline electrolyte. The total loss of capacitance after 7,000 cycles in acidic media is 8 % at 0.6 V and 16 % at 1 V, whereas in the basic electrolyte the reduction in the capacitance values is 72 %, even at a very small operating voltage (0.6 V). This wide range of applications related to their fast energy delivery (e.g. telecommunications systems, maintenance-free traffic lights, uninterruptible power sources, and hybrid electric vehicles among others) [1]. The storage of energy in electrochemical capacitors can arise from either electrostatic charging or from pseudocapacitative chage-discharge [2]. In the first case, electrolyte ions are accumulated at the electrode/electrolyte interface forming the socalled double layer in a similar way as in conventional capacitors. By utilizing high surface area electrodes the amount of charge stored, and consequently the capacitance of the device, is several orders of magnitude higher than that of conventional electrolytic capacitors. In the second case, pseudocapacitance arises from faradaic processes of electroactive species, such as polymeric materials [3], metal oxides [4,5] and certain functionalities at the surface of carbon materials [6,7,8].It is generally believed that pseudocapacitance in carbon materials is largely based on the redox reactions of surface quinoid functionalities, whose reduction requires protons to proceed [9,10]. Nevertheless, some other oxygenated functional groups might be electrochemically active at the working potentials of the acidic solutions, such as some pyrone groups [11,6]. Therefore, and as may be expected, faradic phenomena have a large dependence on the pH of the solution. In this sense, enormous differences in capacitance values can be found depending on the electrolyte used. For carbon materials in neutral solutions, specific capacitance values between 8-12 μF cm -2 have been reported and between 15-20 μF cm -2 in the case of acidic media [12]. Despite that its study is not so frequent, redox reactions in basic media are also possible [13]. In general terms, the presence of the so-called pseudocapacitance has been related in literature to poor cycle life [19] contrary to what occurs in organic media, where only purely charge separation occurs and good cycling stability is typically reported [20]. Investigations in this field are rarely reported, despite that the cyclability of supercapacitors is a property of mayor importance. The present work investigates the effect of the electrolyte (basic or acidic)in the long-term stability of carbon-based supercapacitors. The electro-oxidation of the activated carbon M-AC was carried out in a conventional three-electrode system. Around 100 mg of material was subjected to +0.4 V vs. NHE in a N 2 bu...

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“…[7] Die architektonische Verbesserung der Elektrodenoberflä-chen hin zu einem besseren Nutzungsgrad hätte weitreichende Folgen für Energiespeicherungs-und Umwandlungstechnologien wie Kondensatoren, Batterien, Brennstoffzellen und Elektrolysatoren.…”

Section: Einführungunclassified

Elektrodenarchitektur in galvanischen und elektrolytischen Energiezellen

Jeong¹,

Ocon

Lee³

2016

Angewandte Chemie

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Elektroden in galvanischen und elektrolytischen Brennstoffzellen sind komplizierte Strukturen aus redoxaktiven Materialien, Ionen‐/Elektronenleitern und Porenpfaden für den Stoffaustausch von Reaktanten. Im Gegensatz zu bahnbrechenden Neuerungen bei der Entwicklung der Einzelkomponenten sind die Methoden zur architektonischen Optimierung des Gesamtsystems auf größtmögliche Leistung weniger gut untersucht. In unserem Kurzaufsatz stellen wir allgemeine Typen der Elektrodengestaltung vor, diskutieren Herstellungsstrategien und beschreiben bereits hergestellte Strukturen. Systematisches Optimieren von Elektrodenkonfigurationen kann seit langem bestehende Diskrepanzen zwischen den Gesamtsystemen und den “Summen ihrer Teile” bei verschiedenen elektrochemischen Reaktionen und Technologien auflösen.

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Double Layer Capacitance and Charging Rate of Ultramicroporous Carbon Electrodes

Cited by 115 publications

References 12 publications

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

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

Long-term cycling of carbon-based supercapacitors in aqueous media

Elektrodenarchitektur in galvanischen und elektrolytischen Energiezellen

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