Mechanistic Insights into the Nucleation and Growth of Poly(2,5-dihydroxy aniline) Films Shaped by Scan Rates and Its Impact on Their Charge Capacity

This paper delves into the detailed investigation of the nucleation and growth of poly(2,5-dihydroxy aniline) (PDHA) using cyclic voltammetry (CV) at two scan rates (ν) of 10 mV·s^–1 and 50 mV·s^–1. PDHA is a redox-active conducting polymer comprised of polyaniline (PANI) molecules as a conducting backbone and a redox-active quinone as a pendant group. Electropolymerization was carried out by cycling the potential between −0.2 V and +1.0 V at the two distinct ν, promoting diffusion and kinetically controlled nucleation and growth processes. At a slower ν of 10 mV·s^–1, progressive nucleation forms a rough, porous 3D film. In contrast, rapid ν = 50 mV·s^–1 results in instantaneous nucleation, yielding a compact and flat film. The morphological differences (porous and compact) introduce uncompensated resistance (R_u) variations within the polymer films, influencing the charge storage capacity and other key electrochemical properties. Analysis of the peak current and potential behavior, including the nucleation cycle and subsequent cycles, reveals the underlying mechanisms driving the nucleation and growth of PDHA at both ν. Both types of PDHA films were successfully deposited onto electrochemically etched fibers (ECF). The PDHA film prepared at 10 mV·s^–1 exhibited outstanding electrochemical performance, achieving a mass-normalized specific capacitance (C_m) of 1058 F·g^–1 at a current density of 1 A·g^–1. It also demonstrated excellent cycling stability, maintaining performance over 1000 cycles and up to 7000 cycles in a symmetric setup at 20 A·g^–1, paving the way for innovative applications in energy storage devices. Both films were characterized using CV, GCD, EIS, FEG-SEM, ATR-FTIR, Raman, and UV–Vis techniques to further elucidate this promising material’s properties and behavior.