Proton-Selective Environment in the Pores of Activated Molecular Sieving Carbon Electrodes

Eliad, Linoam; Salitra, Gregory; Soffer, and Abraham; Aurbach, Doron

doi:10.1021/jp020336q

Cited by 30 publications

(34 citation statements)

References 19 publications

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“…17,18 The adsorption of hydrogen may be substantial even in the absence of surface oxides. 18,30,31 We assume in this work that the only species generated by negative polarization is hydrogen in different states of adsorption, because the only chemical species existing inside the nanopores are K + , OH − , and H 2 O. Thus, we neglect possible bound oxygen in the pristine or further pretreated carbon.…”

mentioning

confidence: 99%

Characterization of the Electrochemical and Ion-Transport Properties of a Nanoporous Carbon at Negative Polarization by the Single-Particle Method

Zuleta

Björnbom

Lundblad

2006

J. Electrochem. Soc.

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In this work, the electrochemical processes occurring in a nanoporous carbon, obtained from silicon carbide and used as negative electrode material for supercapacitors, have been investigated by means of the single-particle microelectrode method. The processes studied deal with hydrogen adsorption, evolution, and oxidation using 6 M KOH as electrolyte. It was found that adsorption of hydrogen started at −0.5 V, hydrogen evolution at −1.4 V vs Hg͉HgO, and that hydrogen oxidation occurs in two steps. The first oxidation process takes place between 0 and 0.1 V, shown by a well-defined current peak on the voltammograms. The second oxidation stage occurs between 0.1 and 0.5 V, indicated by a successive increase in current with the number of cycles. It was also found that after the first oxidation process, subsequent cycling between −0.5 and −1 V leads to a larger accumulation of hydrogen inside the nanopores and to a decrease of the effective diffusion coefficient ͑D eff ͒ of potassium ions. Subsequent oxidation, in a second process, leads to a total consumption of hydrogen and to an increase of D eff .As an active component of electrodes for double-layer capacitors ͑DLCs͒, porous carbon materials bring together important characteristic features such as chemical inertness, low cost, and availability in different structural forms. Many of these carbons have different grades of graphitization, microtexture, and porosity, covering sizes from nanopores to macropores. 1,2 One of the reasons for using porous carbon for DLC electrodes is the relative electrochemical inertness of carbon, which allows for wide potential range of operation in capacitor applications. In aqueous solutions, for instance, the range is 0.8-1 V and between 3 and 5 V in organic solutions. As opposed to batteries, the current obtained in a charge and discharge process from a DLC is, theoretically, the result of pure electrostatic driving forces without electron-transfer reactions in the electrode system. Apparently, the potential range of operation is solely delimited by the decomposition of water into hydrogen at negative potential and oxygen at positive potential for aqueous electrolytes. However, it is well known 1 that real carbon electrodes for DLC do not strictly follow this electrochemical behavior. Thus, besides the capacitive processes occurring within the operation limits, other processes of faradaic nature take place simultaneously on the carbon surface. 3,4 Intensive investigations have been dedicated to the study of electrolytic processes occurring at positive electrodes, such as oxidation and corrosion in both alkali and acid media, also of great importance for the performance of batteries and bifunctional air electrodes. The principal reason for this scientific or technical interest is the fact that the oxidative processes cause changes in the surface morphology of the carbon materials, affecting the electrode performance. 5 The studies made in this field have revealed, for instance, that oxidation of carbon starts at lower potentials th...

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mentioning

confidence: 99%

Characterization of the Electrochemical and Ion-Transport Properties of a Nanoporous Carbon at Negative Polarization by the Single-Particle Method

Zuleta

Björnbom

Lundblad

2006

J. Electrochem. Soc.

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“…In order to obtain carbon samples that were poor in oxygen-containing surface groups, a chemical reduction using an Ar/H 2 flow at 900°C was employed [10]. The XPS data of these samples confirms that their oxygen content was indeed lower than the oxygen content in the carbon samples that were treated in HNO 3 solution.…”

Section: Resultsmentioning

confidence: 94%

“…Thereby, these samples have a smaller surface area compared to the pristine CO 2 activated carbon samples. Chemical reduction using Ar/ H 2 at 900°C reduces the content of oxygen-containing surface groups present on the carbon samples [10,13]. Thus, the specific area of these samples was somewhat larger than that of the samples activated only by CO 2 at 900°C and stored under ambient conditions.…”

Section: Resultsmentioning

confidence: 95%

“…Chemical activation with HNO 3 solutions oxidizes the carbon surface [12], yet due to the low temperatures employed in this activation method (RT), the extent of gasification of the surface groups thus formed is markedly less pronounced than in the case of the activation using CO 2 at 900°C. The surface groups thus formed on the surface of the carbon samples hinder the penetration of N 2 molecules into the carbon's pore system [10]. Thereby, these samples have a smaller surface area compared to the pristine CO 2 activated carbon samples.…”

Section: Resultsmentioning

confidence: 99%

“…The first type underwent chemical activation, in order to form carbons enriched with surface groups, by dipping the carbon samples in nitric acid solutions (60% w/w in water) [10] for 0.5 h at RT. The second type of carbon samples underwent a chemical reduction process in order to reduce the content of oxygen-containing groups from the carbon surface at 900°C under Ar/H 2 flow (95%/5%, Oxygen & Argon Works, Israel) for 1 h [10]. These samples were then stored under high-purity argon in a glove box (M. Braun, Inc.) in order to prevent the reformation of surface groups in the presence of oxygen from the air.…”

Section: Methodsmentioning

confidence: 99%

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