Study on capacitance evolving mechanism of polypyrrole during prolonged cycling
JingPing Wang1, Youlong Xu, Jie Wang
1College of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology , Xi'an 710021, China.
The Journal of Physical Chemistry. B
|January 17, 2014
Summary
Polypyrrole (PPy) capacitance initially increases but rapidly decays due to salt accumulation. This salt buildup hinders ion transport and reduces conductivity, impacting PPy supercapacitor performance over extended cycling.
Area of Science:
- Electrochemistry
- Materials Science
- Polymer Science
Background:
- Polypyrrole (PPy) is a promising material for supercapacitors.
- Understanding capacitance evolution in PPy is crucial for device longevity.
Purpose of the Study:
- To investigate the mechanism behind the rapid increase and decay of PPy capacitance during prolonged cycling.
- To correlate changes in PPy properties with its electrochemical performance.
Main Methods:
- Electrochemical cycling of PPy films in 1 M 1-ethyl-3-methylimidazolium tetrafluoroborate/propylene carbonate (EtMeImBF4/PC) electrolyte.
- Fourier-transform infrared (FTIR) spectroscopy to monitor salt presence.
- Electrochemical Quartz Crystal Microbalance (EQCM) to analyze ion insertion.
Main Results:
- PPy films achieved a high specific capacitance of 420 F·g(-1) after 15 cycles.
- Capacitance rapidly decreased to 5% of its initial value after 400 cycles.
- Decreased electronic conductivity and protonation level were observed with increased cycling.
- Accumulation of 1-ethyl-3-methylimidazolium (EtMeIm(+)) cations and BF4(-) anions within the PPy matrix was confirmed.
Conclusions:
- Initial high capacitance is attributed to salt-induced ion transport channels.
- Rapid capacitance decay is linked to the continuous combination of EtMeIm(+) with doping anions (PTS(-)), leading to reduced protonation and a compensated semiconductor state.
- Increased PPy internal resistance due to salt accumulation significantly impacts long-term performance.
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