ISO-PROPANOL AS A SURFACE UNBLOCKING AGENT FOR CARBON NANOTUBE–POLYPYRROLE COMPOSITE
Larysa I. Hromadska 1, Denys G. Gromadskyi 2,
1 Institute for Sorption and Problems of Endoecology, National Academy of Sciences of Ukraine, Kyiv, Ukraine;
2 Joint Department of Electrochemical Energy Systems, National Academy of Sciences of Ukraine, Kyiv, Ukraine
Electroconducting polymers are used in the electrodes for supercapacitors to increase their specific energy. ‘Traditional’ carbon-based electrodes are covered by thin layer of polypyrrole giving pseudocapacitance effect due to the anion intercalation/deintercalation process. Such composite materials are commonly utilized with aqueous electrolytes [1, 2]:
PPy(A–) + e = PPy0 + A–,
where PPy – polypyrrole; A– – anion (Cl–, SO42–, NO3–, etc.).
But it is well known that carbon materials are mainly hydrophobic by nature . Moreover, electrolyte solutions have higher values of surface tension than pure solvents . This leads to problem with an impregnation of the electrodes by the water-based electrolytes. And, as a result, their active surface cannot be realized fully.
Fig. 1 Cyclic voltammetry of carbon nanotube–polypyrrole composite at 5 mV/s: dashed line – original electrolyte (3M KCl in water); solid line – improved electrolyte (3M KCl in water + 10 vol. % iso-propanol).
Adding the surfactant (iso-propanol) to the electrolyte solution allows solving this issue, because molecules of alcohol, adsorbing on the carbon framework, reduce the surface tension and facilitate the ion access inside porous structure of the electrode .
As it shown from figure listed above, carbon nanotube–polypyrrole composite with water–iso-propanol solution has higher specific capacitance than electrode operating in original electrolyte (165 and 193 F/g, respectively). This will give an increase of the specific energy for a supercapacitor up to 15 %.
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