QCM-D study of electrochemical synthesis of 3D polypyrrole thin films for negative electrodes in supercapacitors

Abstract Polypyrrole (PPy) is a conducting polymer widely investigated for many purposes, including as an electroactive material in supercapacitors. In this work, we studied the electropolymerization of PPy using methyl orange as a template to obtain thin films of PPy hydro-sponges. The growth of the films was performed by cyclic voltammetry and potentiostatic steps coupled with a quartz crystal microbalance measuring changes in frequency and energy dissipation. We found that methyl orange does not have an impact on the electropolymerization process in addition to its role in determining the microfibrillar structure, resulting in microfibers with diameters ranging from 500 to 900 nm, which is larger than the microfibers obtained in the chemical route with methyl orange. Changes in frequency and energy dissipation indicated that the film growth is similar when 0.45, 0.50 or 0.6 V vs Ag/AgCl NaCl 3M is applied, However, the chronoamperometric measurements show a larger increase in current density for the highest potential, suggesting that the growth of microfibers increases the surface area, which is responsible for the higher current density. Measurement of roughness using Atomic Force Microscopy for different chronoamperometry durations confirmed the increase in surface area as more PPy hydro-sponge is electropolymerized. Supercapacitors were assembled using an electrode of PPy hydro-sponge electropolymerized onto stainless steel as a negative electrode and activated carbon as a positive one. The capacitance of the PPy hydro-sponge electrode was estimated to be approximately 100 F g-1, while the two-electrode cell achieved 17 F g-1 while operating at 0.1 A g-1.