Short communicationPreparation and electrochemical capacitance performances of super-hydrophilic conducting polyaniline
Introduction
Electrochemical capacitors, also called supercapacitors, have attracted great interest as an important energy-storage/conversion device [1], [2]. Nowadays, high-surface activated carbons, noble metal oxides and conducting polymers are the main families of electrode materials for electrochemical capacitors [3], [4], [5].
Polyaniline is one of the most extensively investigated conducting polymers because of its good stability, low cost, and unique doping/de-doping mechanism [6], [7]. For the electrochemical capacitor application, it is important to synthesize nano-size polyaniline, because they show better rates and larger capacities than traditional materials. Within the nano-structured electrode material, the transportation distance of ions in electrolyte is smaller than within the conventional electrode material with the same chemical composition [8], [9], [10], [11], [12]. Now, nano-size polyaniline with different morphologies have been synthesized by many methods [13], [14], [15], [16], [17], and their electrochemical capacitance performances as an electrode material have also been reported [18], [19], [20], [21], [22]. However, we think that super-hydrophilicity of electrode materials should also be considered for aqueous redox supercapacitors, because good hydrophilicity is advantageous to the diffusion of aqueous electrolyte during the charge/discharge process.
Here we describe an inexpensive and simple route to the preparation of super-hydrophilic conducting polyaniline by surface modification of polyaniline using tetraethyl orthosilicate in water/ethanol solution. What is particularly exciting is that the surface modification enables the formation of abundant mesopores in polyaniline, which contributes excellent electrochemical capacitance performances to polyaniline electrode material. The electrochemical investigations show that its specific capacitance is 500 F g−1 at a constant current density of 1.5 A g−1 in 0.1 M H2SO4 aqueous solution, and the capacitance retention ratios reaches circa 70% with the growth of current densities from 1.5 to 20 A g−1. It would have a great potential for aqueous redox supercapacitors application.
Section snippets
Experimental
Aniline (Shanghai Chemical Works, China) was redistilled before use, while tetraethyl orthosilicate (Shanghai Medical and Chemical Works, China) was used without further purification. Other chemicals used were of analytical reagent grade.
Preparation of conducting polyaniline (PAn) was shown as follows. First, 0.9 ml of aniline was injected into 80 ml of 1.5 M HCl, and then 2.28 g of (NH4)2S2O8 (APS) (dissolved in 20 ml of de-ionized water) was quickly added into above solution. The mixture was kept
Morphology and surface properties
SEM and contact angles of SH-PAn and PAn are given in Fig. 1. Fig. 1 shows that SH-PAn is irregular granule. Comparing Fig. 1a with c, it is obvious that the morphology of PAn has some changes after the surface modification. However, the contact angle of SH-PAn for aqueous solution is 0°, indicating that SH-PAn is of super-hydrophilicity, and the contact angle of PAn is about 81°.
In order to investigate the effects of the surface modification on surface area, average pore size and pore size
Conclusion
A novel method is found to prepare polyaniline with good electrochemical capacitance performances for aqueous redox supercapacitors. TEOS polycondensate endows polyaniline with super-hydrophilic property and creates plentiful mesoporous structures, which provide a fast and short diffusion approach for the aqueous electrolyte. As an electrode material, it shows large specific capacitance, high rate capability and good cycle stability in 0.1 M H2SO4 aqueous solution. Its specific capacitance is 500
Acknowledgements
We are grateful for the financial support from the Shanghai Municipal Science and Technology Commission (0852nm02000), Shanghai Leading Academic Discipline Project (B502) and Shanghai Key Laboratory Project (08DZ2230500).
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