Electrochemical behavior of polydiphenylamine-2-carboxylic acid and its hybrid nanocomposites with single-walled carbon nanotubes on anodized graphite foil in lithium aprotic electrolyte

Abstract

Electrochemical properties of novel electrode coatings based on polydiphenylamine-2-carboxylic acid (PDPAC) and its hybrid nanocomposites with single-walled carbon nanotubes (SWCNT) were studied for the first time. PDPAC and SWCNT/PDPAC nanomaterials were synthesized via in situ oxidative polymerization in the homogeneous acidic medium (in 5 М H2SO4) and in the heterophase system in an alkaline medium (in a mixture of chloroform and NH4OH). Hybrid electrodes are flexible strips of anodized graphite foil (AGF) with electroactive layers of stable suspensions of polymers and nanocomposites in formic acid (FA) formed on their surface, without any binding and electrically conductive additives. The roughened surface and presence of oxygen-containing groups on the AGF surface provide good adhesion of the electroactive coatings. The use of the modified graphite foil as a current collector leads to a significant increase in the electrochemical capacitance and stability of the coatings. The specific electrochemical capacitance of electroactive coatings on AGF depends on the reaction medium pH for the coatings synthesis and reaches 421, 258, 150 F∙g−1 for PDPACac and 438, 350, 259 F∙g−1 for SWCNT/PDPACac, prepared in an acidic medium (pH = 0.3), and 202, 106, 63 F∙g−1 for PDPACalk and 278, 191, 129 F∙g−1 for SWCNT/PDPACalk, obtained in an alkaline medium (pH = 11.4), at charge-discharge currents of 0.5, 1.5, 3.0 mА·cm−2, respectively, in 1 М LiClO4 organic electrolyte in propylene carbonate. The PDPAC and SWCNT/PDPAC electroactive coatings are characterized by high stability of electrochemical properties at Coulombic efficiency up to 96–100%. The main contribution to the electrochemical capacitance is provided by the charging of the electric double layer.