Impedimetric studies about the degradation of polypyrrole nanotubes during galvanostatic charge and discharge cycles

Polypyrrole nanotubes (PPyNTs) are interesting materials that can be used as supercapacitors due to the high conductivity in the doped state and large surface area, but the limited cycling stability is a common issue that restrict further applications. The loss of capacitance during galvanostatic charge/discharge (GCD) cycles are commonly observed and the reasons for this lack of stability remain unclear. Herein, we demonstrate the changes in the electrode/electrolyte interface during 500 GCD cycles by using electrochemical impedance spectroscopy to understand how the continuous cycling affect the electroactivity of the PPyNTs, a proper discussion of the use of this technique is present as well. The results were supported by scanning electron microscopy images, Raman and UV-Vis spectroscopies, that evidenced the electrochemical degradation of PPyNTs during the GCD cycles caused mainly by changes in the morphology, which affects the charge transfer and charge intercalation processes and the expulsion of template molecules during the GCD cycles, causing an increment in the charge intercalation within the conducting polymer matrix.