Diffuse charge and Faradaic reactions in porous electrodes
Porous electrodes instead of flat electrodes are widely used in electrochemical systems to boost storage capacities for ions and electrons, to improve the transport of mass and charge, and to enhance reaction rates. Existing porous electrode theories make a number of simplifying assumptions: (i) T...
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| Aineistotyyppi: | Artikkeli |
| Kieli: | en_US |
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American Physical Society
2011
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| Linkit: | http://hdl.handle.net/1721.1/66952 |
| _version_ | 1826190435293331456 |
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| author | Biesheuvel, P. M. Fu, Yeqing Bazant, Martin Z. |
| author2 | Massachusetts Institute of Technology. Department of Chemical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Chemical Engineering Biesheuvel, P. M. Fu, Yeqing Bazant, Martin Z. |
| author_sort | Biesheuvel, P. M. |
| collection | MIT |
| description | Porous electrodes instead of flat electrodes are widely used in electrochemical systems to boost storage
capacities for ions and electrons, to improve the transport of mass and charge, and to enhance reaction rates.
Existing porous electrode theories make a number of simplifying assumptions: (i) The charge-transfer rate is
assumed to depend only on the local electrostatic potential difference between the electrode matrix and the pore
solution, without considering the structure of the double layer (DL) formed in between; (ii) the charge-transfer
rate is generally equated with the salt-transfer rate not only at the nanoscale of the matrix-pore interface, but also
at the macroscopic scale of transport through the electrode pores. In this paper, we extend porous electrode theory
by including the generalized Frumkin-Butler-Volmer model of Faradaic reaction kinetics, which postulates charge
transfer across the molecular Stern layer located in between the electron-conducting matrix phase and the plane
of closest approach for the ions in the diffuse part of the DL. This is an elegant and purely local description of the
charge-transfer rate, which self-consistently determines the surface charge and does not require consideration of
reference electrodes or comparison with a global equilibrium. For the description of the DLs, we consider the
two natural limits: (i) the classical Gouy-Chapman-Stern model for thin DLs compared to the macroscopic pore
dimensions, e.g., for high-porosity metallic foams (macropores >50 nm) and (ii) a modified Donnan model for
strongly overlapping DLs, e.g., for porous activated carbon particles (micropores <2 nm). Our theory is valid
for electrolytes where both ions are mobile, and it accounts for voltage and concentration differences not only on
the macroscopic scale of the full electrode, but also on the local scale of the DL. The model is simple enough to
allow us to derive analytical approximations for the steady-state and early transients. We also present numerical
solutions to validate the analysis and to illustrate the evolution of ion densities, pore potential, surface charge,
and reaction rates in response to an applied voltage. |
| first_indexed | 2024-09-23T08:40:12Z |
| format | Article |
| id | mit-1721.1/66952 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T08:40:12Z |
| publishDate | 2011 |
| publisher | American Physical Society |
| record_format | dspace |
| spelling | mit-1721.1/669522022-09-30T10:22:37Z Diffuse charge and Faradaic reactions in porous electrodes Biesheuvel, P. M. Fu, Yeqing Bazant, Martin Z. Massachusetts Institute of Technology. Department of Chemical Engineering Massachusetts Institute of Technology. Department of Mathematics Bazant, Martin Z. Fu, Yeqing Bazant, Martin Z. Porous electrodes instead of flat electrodes are widely used in electrochemical systems to boost storage capacities for ions and electrons, to improve the transport of mass and charge, and to enhance reaction rates. Existing porous electrode theories make a number of simplifying assumptions: (i) The charge-transfer rate is assumed to depend only on the local electrostatic potential difference between the electrode matrix and the pore solution, without considering the structure of the double layer (DL) formed in between; (ii) the charge-transfer rate is generally equated with the salt-transfer rate not only at the nanoscale of the matrix-pore interface, but also at the macroscopic scale of transport through the electrode pores. In this paper, we extend porous electrode theory by including the generalized Frumkin-Butler-Volmer model of Faradaic reaction kinetics, which postulates charge transfer across the molecular Stern layer located in between the electron-conducting matrix phase and the plane of closest approach for the ions in the diffuse part of the DL. This is an elegant and purely local description of the charge-transfer rate, which self-consistently determines the surface charge and does not require consideration of reference electrodes or comparison with a global equilibrium. For the description of the DLs, we consider the two natural limits: (i) the classical Gouy-Chapman-Stern model for thin DLs compared to the macroscopic pore dimensions, e.g., for high-porosity metallic foams (macropores >50 nm) and (ii) a modified Donnan model for strongly overlapping DLs, e.g., for porous activated carbon particles (micropores <2 nm). Our theory is valid for electrolytes where both ions are mobile, and it accounts for voltage and concentration differences not only on the macroscopic scale of the full electrode, but also on the local scale of the DL. The model is simple enough to allow us to derive analytical approximations for the steady-state and early transients. We also present numerical solutions to validate the analysis and to illustrate the evolution of ion densities, pore potential, surface charge, and reaction rates in response to an applied voltage. 2011-11-07T15:36:38Z 2011-11-07T15:36:38Z 2011-06 2011-01 Article http://purl.org/eprint/type/JournalArticle 1539-3755 1550-2376 http://hdl.handle.net/1721.1/66952 Biesheuvel, P., Yeqing Fu, and Martin Bazant. “Diffuse Charge and Faradaic Reactions in Porous Electrodes.” Physical Review E 83.6 (2011) : 061507. en_US http://dx.doi.org/10.1103/PhysRevE.83.061507 Physical Review E Creative Commons Attribution-Noncommercial-Share Alike 3.0 http://creativecommons.org/licenses/by-nc-sa/3.0/ application/pdf American Physical Society MIT web domain |
| spellingShingle | Biesheuvel, P. M. Fu, Yeqing Bazant, Martin Z. Diffuse charge and Faradaic reactions in porous electrodes |
| title | Diffuse charge and Faradaic reactions in porous electrodes |
| title_full | Diffuse charge and Faradaic reactions in porous electrodes |
| title_fullStr | Diffuse charge and Faradaic reactions in porous electrodes |
| title_full_unstemmed | Diffuse charge and Faradaic reactions in porous electrodes |
| title_short | Diffuse charge and Faradaic reactions in porous electrodes |
| title_sort | diffuse charge and faradaic reactions in porous electrodes |
| url | http://hdl.handle.net/1721.1/66952 |
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