Tetracarboxylic Acid-Doped Polyaniline Nanotubes: Effect of the Dopant Structure on the Morphology, Charge Storage Capacity, and Cycle Stability

Tetracarboxylic acid-doped polyaniline (PANI) nanotubes have been developed using a green approach in an aqueous medium via single-step chemical oxidation polymerization of aniline monomers utilizing ammonium persulfate (APS) as an oxidant. Subsequently, these nanotubes have been employed as electrode materials to investigate their capacitive behavior. To explore the effect of the dopant structure on the overall morphology and capacitive properties, two tetracarboxylic acids, ethylenediamine tetraacetic acid (EDTA), an aliphatic acid that is flexible in nature, and benzene tetracarboxylic acid (BTCA), an aromatic acid that is rigid in nature, are judiciously chosen. After characterizing these PANI structures using absorption, FT-IR spectroscopy, XRD, TGA, and extensive electrochemical studies, symmetrical all-solid-state devices have been fabricated using these structures to investigate and compare the device parameters. The EDTA-PANI nanotubes exhibit a specific capacitance of 176.9 F g–1 at a current density of 0.5 A g–1, with an energy density of 15.72 Wh kg–1 and a power density of 200 W kg–1. In contrast, the BTCA-PANI system demonstrates a specific capacitance of 150.06 F g–1 at the same current density, with energy and power densities of 13.3 Wh kg–1 and 200 W kg–1, respectively. Impressively, supercapacitors made of EDTA-PANI reveal 72.5% retention of specific capacitance over 20,000 galvanostatic charge–discharge cycles, whereas BTCA-PANI displays 40% retention of specific capacitance at identical conditions, indicating the prolonged stability of EDTA-PANI as well as the superior electrode material from the perspective of electrochemical energy storage systems. Subsequently, a laboratory-based supercapacitor is assessed by lighting a red LED to reveal the potential of EDTA-PANI as an excellent organic energy material.