Acid-doped polyaniline and its vertically aligned SWCNT composites: Influence of acid type and concentration on structural and electrochemical properties

This study explores how acid type (hydrochloric acid [HCl], p-toluenesulfonic acid [TSA], and formic acid [FA]) and concentration affect the structure of polyaniline (PANI) and the electrochemical properties of its composite with vertically aligned single-walled carbon nanotubes (SWCNTs). PANI doped with TSA (PANI-TSA) exhibited improved dispersion and conjugation attributed to the larger anion volume, which mitigates interchain spacing, in contrast to PANI doped with HCl (PANI-HCl) and FA (PANI-FA). Additionally, varying the organic acid concentration affected PANI's morphology and the concentration of quinone structure, with TSA leading to a fibrous structure and enhanced electrochemical characteristics. The study further investigated the SWCNTs/PANI composite, revealing that higher TSA concentrations enhance conductivity and specific capacitance of the composite membrane due to sulfonic acid group. Notably, HCl-based SWCNTs/PANI only at higher acid concentrations exhibits superior electrochemical characteristics than TSA-based SWCNTs/PANI, achieving charge transfer resistance down to 5.514 Ω cm 2 at 1.0 mol/L. Moreover, applying an electric field during membrane synthesis significantly increased the specific capacitance of composite prepared with PANI-TSA, highlighting the role of voltage in optimizing electron transport efficiency within the composite.