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Ionic transport in pores in activated carbons for EDLCs
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Reaction Engineering.
2006 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, Vol. 153, no 10, A1914-A1921 p.Article in journal (Refereed) Published
Abstract [en]

The transport properties and morphology of an activated carbon containing macro-, meso-, and micropores were studied and compared to a sophisticated fully nanoporous carbon that almost lacks meso- and macropores. The morphology of the activated carbon was studied using nitrogen adsorption methods and the pore size distribution was investigated using Barret, Joyner, and Halenda and density functional theory models. The transport properties were studied using a microelectrode technique that allows for determination of the effective diffusivity, D-eff. For the meso/macroporous carbon the effective diffusivity was determined using potential step experiments and analysis for both Cottrell and filling diffusivities were made. The Cottrell diffusivity was smaller than the value of the filling diffusivity, with mean values of (9.4 +/- 3.8) x 10(-14) m(2) s(-1) and (3.1 +/- 1.6) x 10(-12) m(2) s(-1), respectively. This difference in diffusivities is the basis for an agglomerate hypothesis presented for the meso/macroporous carbon. The results for the meso/macroporous carbon are compared with the corresponding results for the sophisticated fully nanoporous carbon. This gave further evidence for the presented agglomerate hypothesis.

Place, publisher, year, edition, pages
2006. Vol. 153, no 10, A1914-A1921 p.
Keyword [en]
Adsorption; Mathematical models; Mesoporous materials; Microelectrodes; Morphology; Nitrogen; Pore size; Probability density function; Transport properties; Agglomerate hypothesis; Barret models; Cottrell diffusivity; Filling diffusivity; Joyner models; Activated carbon
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7547DOI: 10.1149/1.2335613ISI: 000240312000019Scopus ID: 2-s2.0-33748436521OAI: oai:DiVA.org:kth-7547DiVA: diva2:12605
Note
QC 20100809Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2010-08-09Bibliographically approved
In thesis
1. Nanoscientific investigations of electrode materials for supercapacitors
Open this publication in new window or tab >>Nanoscientific investigations of electrode materials for supercapacitors
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This doctoral thesis gives background to the field of electrochemical energy storage in supercapacitors. It attempts to place the supercapacitor device in context of available and future technologies for alternative energy systems for transportation. Limitations of cells and electrodes and key challenges in the supercapacitor development are introduced. One objective of the thesis is to investigate and describe ionic transport in active carbon and possible restrictions in nanostructured porous systems with focus on small (micro and meso) pores. Another is to develop a model suitable for investigations of concentration and potential profiles from a single particle perspective. The results from the studies are presented in this thesis together with the scientific papers this thesis is based on.

Studying electrochemical gradients (concentration and potential) of large electrodes and single particles may give important information of the limitations of the material. In larger three-electrode experimental set-ups, these gradients can be studied for electrodes but single particles are not available for experimental studies to the same extent since the matrix of an electrode consist of many particles, all adding to the total gradient of the electrode. The experimental part of this thesis is based on different experimental techniques: Three-electrode experiments for larger electrodes, microelectrode experiments for single particles, numerical simulations using Multiphysics (software) of large electrodes consisting of single particles.

Four Papers are appended to the thesis. They present results and discussions regarding ionic transport, surface functionalities and modeling of a particle based supercapacitor electrode. Estimated effective diffusivities for an active carbon containing micro, meso and macropores are presented. Surface functionalities in the form of oxygen-containing groups were present in a carbon studied using two experimental set-ups. Faradaic peaks, previously not reported in activated carbon were seen. The occurrence of Faradaic phenomena in one experimental set-up but not the other is further analyzed and the origin of these peaks discussed. The particle based mathematical model, where galvanostatic and cyclic voltammetry is simulated, is presented. Concentration profiles both in the particles and electrodes are discussed and some of the numerical results are compared with experimental data.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. iv, 82 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:64
Keyword
Supercapacitor, double layer, microelectrode, ionic transport
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4508 (URN)978-91-7178-767-5 (ISBN)
Public defence
2007-11-08, F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100809Available from: 2007-10-17 Created: 2007-10-17 Last updated: 2010-08-09Bibliographically approved

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