Abstract
The use of ionic liquid (IL) electrolytes promises to improve the energy density of electrochemical
capacitors (ECs) by allowing for operation at higher voltages. Several studies have also shown that
the pore size distribution of materials used to produce electrodes is an important factor in determining
EC performance. In this research the capacitative, energy and power performance of ILs 1-ethyl-3-
methylimidazolium tetrafluoroborate (EMImBF4), 1-ethyl-3-methylimidazolium dicyanamide
(EMImN(CN)2), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide
(DMPImTFSI), and 1-butyl-3-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate
(BMPyT(F5Et)PF3) were studied and compared with the commercially utilised organic electrolyte 1M
tetraethylammonium tetrafluoroborate solution in anhydrous propylene carbonate (Et4NBF4–PC
1 M). To assess the effect of pore size on IL performance, controlled porosity carbons were produced
from phenolic resins activated in CO2. The carbon samples were characterised by nitrogen adsorption–
desorption at 77 K and the relevant electrochemical behaviour was characterised by cyclic
voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The best
capacitance performance was obtained for the activated carbon xerogel with average pore diameter
3.5 nm, whereas the optimum rate performance was obtained for the activated carbon xerogel with
average pore diameter 6 nm. When combined in an EC with IL electrolyte EMImBF4 a specific
capacitance of 210 F g1 was obtained for activated carbon sample with average pore diameter 3.5 nm
at an operating voltage of 3 V. The activated carbon sample with average pore diameter 6 nm allowed
for maximum capacitance retention of approximately 70% at 64 mA cm2.
Original language | English |
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Pages (from-to) | 695-706 |
Number of pages | 12 |
Journal | Energy and Environmental Science |
Volume | 4 |
Issue number | 3 |
DOIs | |
Publication status | Published - Mar 2011 |
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- Environmental Chemistry
- Pollution
- Nuclear Energy and Engineering