Control of Morphology and Band Gap in Electrosynthesized Polypyrrole: Role of Nucleation and Growth Mechanisms

Polypyrrole (PPy) is one of the most extensively studied conducting polymers due to its favorable optical properties and electrical conductivity. In this work, the relationship between the morphology of nuclei formed during electrochemical synthesis and the electronic properties of PPy is investigated, with particular emphasis on controlling nu-cleation and growth mechanisms (NGM). Polymerization was carried out electrochemi-cally in acetonitrile containing pyrrole as the monomer and LiClO4 (0.1 M) as the sup-porting electrolyte. Potentiodynamic techniques, specifically cyclic voltammetry (CV), were used to establish the synthesis conditions, while potentiostatic techniques, such as chronoamperometry, were employed to analyze NGM and achieve morphological con-trol. The resulting polymeric films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis spectroscopy. The optical band gap was estimated using the Tauc method. Three distinct contributions to the NGM of PPy de-posited on indium tin oxide (ITO) conductive glass were identified: instantaneous nu-cleation with two-dimensional growth (IN2D), progressive three-dimensional nucleation controlled by charge transfer (PN3Dct), and progressive three-dimensional nucleation controlled by diffusion (PN3Ddif). When the growth mechanism was controlled, the electrosynthesized PPy exhibited band gap values of 3.31, 3.54, and 3.58 eV. SEM analysis revealed that IN2D leads to the formation of flat and homogeneous nuclei, whereas PN3Dct and PN3Ddif produce denser, more branched structures with growth perpen-dicular to the electrode surface. These findings demonstrate that precise control of NGM enables modulation of the electronic properties of PPy, providing opportunities to op-timize its performance in applications such as electrochemical sensors, supercapacitor electrodes, and organic electronic devices.