Influence of the pH on the electrochemical synthesis of polypyrrole nanotubes and the supercapacitive performance evaluation

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Active materials aiming the development of high performance and flexible electrodes for electrochemical applications is still a big challenge, important features such as ease synthesis, high electroactive area and robustness of modified electrodes must be addressed. In this contribution, polypyrrole nanotubes were electrochemically synthesized onto stainless steel mesh electrodes by using methyl orange aggregates as template for polymerization. The characterization of the obtained material in different experimental conditions were deeply investigated. It was found that the pH value of the electrolyte during synthesis plays a key role on the methyl orange aggregates obtaining by this way different material morphologies with tunable electrochemical properties. In neutral medium, globular polypyrrole is deposited onto the electrode and methyl orange aggregates are adsorbed on the synthesized polymer, whereas in acidic condition the polypyrrole nanotubes are formed, evidenced by different techniques which unfolded the morphologic, structural and electrochemical properties of the modified electrodes. Amongst the different applications for the materials described herein, the pseudocapacitive properties of the modified electrodes were evaluated by cyclic voltammetry and galvanostatic charge/discharge experiments and a maximum specific capacitance of 423 F g−1 at a current density of 0.5 A g−1 was obtained. The mechanical properties of the modified electrodes were tested under torsion and bending conditions, where no drastic change of their supercapacitive properties were found.