Electrogeneration of N-substituted polyaniline micro/nanoparticles with potential for energy storage

In the pursuit to develop functionalized polyaniline (PANI) micro/nanoparticles suitable for electrical charge storage, the electrochemical copolymerization of N-(3-sulfopropyl) aniline (AnPS) and N-(2-hydroxyethyl) aniline (AnEtOH) was performed to generate electroactive N-substituted PANI layers directly deposited onto conductive substrates. A particular attention was focused on the impact of the comonomer's molar ratio and pH of the electrolysis solutions on the morphology and electrochemical properties of PANI electrodeposited layers. Thus, four mixtures of the monomers were subjected to electrochemical polymerization in two electrolyte solutions (1 M H2SO4 and acetate buffer solution, pH 4.5) that led to green, homogeneous copolymer deposition layers on the electrode surface. These provided different structural morphologies, that varied from spherical microparticles generated from solution with slightly acidic pH (4.5) to dense, granular morphological features in the case of the deposition layers electrogenerated from 1 M H2SO4. These were characterized in detail by FT-IR and UV–Vis spectroscopies, which confirmed their proposed chemical structure. The electrooxidative polymerization mechanism of the studied N-substituted aniline monomers was evidenced by spectroelectrochemical studies, which highlighted the influence of the monomer's molar ratio and solutions’ pH on the electrolysis process. Moreover, it was demonstrated that the particle dimensions and distributions can be controlled by the comonomer's molar ratio and electrolysis parameters. Considering that the high specific surface area of the obtained PANI micro/nanoparticles can contribute to a better wettability of the polymer molecules with electrolyte ions and their diffusion, the capacitive behaviour of these PANI films was investigated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD). The highest areal specific capacitance, of 5.32 mFcm−2, was obtained for the polymer electrogenerated from 1:1 molar ratio of the two monomers, that distinguished by the related polymers through a better ion diffusion at low scan rates and efficient charge transfer at high scan rates.