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Dissertation
Pore-size ion-size correlations for carbon supercapacitors
Doctor of Philosophy (Ph.D.), Drexel University
Feb 2009
DOI:
https://doi.org/10.17918/etd-3031
Abstract
Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. This could lead to fleet-wide improvements in economy, performance, lifetime and environmental impact of Hybrid Electric Vehicles (HEVs), as well as enable or advance many other applications. To determine correlations between ion-size and pore-size in carbon supercapacitors, we generated a well-characterized set of porous carbide-derived carbons (CDC) with average pore sizes from 0.6 to 2.25 nm and used them to probe the limits of understanding. Performing the first systematic study of the effect of pore size on capacitance showed that, in general, decreasing the pore size below the size of the solvated ion, or to precisely the size of the ionic liquid ion, allowed higher accumulation of charge. Using CDC with properly tuned porosity showed excellent performance in H₂SO4, ~200 F/g, andperformance superior to all prior reported results in organic (CH3CH2)4NBF4 (TEABF4) electrolytes as well as 1-ethyl-3-methyl immidazolium bis-(trifluoromethanesulfonyl)imide (EMI-TFSI) ionic liquid, ~150 F/g. This work conclusively showed that precisely matching the pore size with the ion size is the key factor for maximizing capacitance. Understanding that pores significantly larger than the effective ion size do not have large contributions to energy storage, work on dense porous CDC films on conductive substrates showed ~100% larger volumetric capacitance than any previously reported. Depositing patterned films of carbide and electrical contacts could lead to microfabricated energy storage devices directly on a chip, or built up in layers for performances yet unrealized.
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Details
- Title
- Pore-size ion-size correlations for carbon supercapacitors
- Creators
- John Chmiola - DU
- Contributors
- Yury Gogotsi (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 3031; 991014632072304721