Study on Capacitance Evolving Mechanism of Polypyrrole during Prolonged Cycling

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• 作者：JingPing Wang ; Youlong Xu ; Jie Wang ; Jianbo Zhu ; Yang Bai ; Lilong Xiong
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：February 6, 2014
• 年：2014
• 卷：118
• 期：5
• 页码：1353-1362
• 全文大小：580K
• ISSN：1520-5207

文摘

A simple model on the evolution mechanism of PPy capacitance during prolonged cycling offers a reasonably description on the rapid increase and decay of PPy capacitance in 1 M 1-ethyl-3-methylimidazolium tetrafluoroborate/propylene carbonate (EtMeImBF₄/PC). The capacitance of PPy films reached a very high specific capacitance of 420 F路g^鈥? after 15 cycles when they worked in 1 M MeEt₃ImBF₄/PC. However, the capacitance rapidly decreased to 5% after only 400 cycles. The electronic conductivity and protonation level on the nitrogen site of PPy films rapidly decreased with the increase of cyclic number. The salt of EtMeImBF₄ was monitored in PPy matrix by FTIR spectra after 400 cycles. The EQCM results indicated that a lot of 1-ethyl-3-methylimidazolium cations (EtMeIm⁺) were inserted during reduction process and retained in PPy matrix. The detained EtMeIm⁺ cations bonded with doped p-toluenesulfonate anions (PTS^{鈥?/sup>) in PPy matrix or BF₄鈥?/sup> anions from electrolyte and formed salts. Small amount of salts in PPy matrix can open more channels of ion insertion and resulted in a very high capacitance after 15 cycles. The continuous combination of detained EtMeIm+ cations with doping anions of PTS鈥?/sup> resulted in the rapid decrease of PPy protonation level on the nitrogen site and formation of compensate semiconductor state in PPy matrix. This should be responsible for the rapid decay of PPy conductivity and capacitance. The continuous accumulation of salts resulted in the great increase of PPy internal resistance.}