Copolymerization of Aniline, Melamine and p-Phenylenediamine for Enhanced Pseudocapacitance Hydrogel Supercapacitor Electrodes

A novel double-crosslinked 3D network hydrogel, poly(aniline-co- p -phenylenediamine-co-melamine) (PD 2 M 4 ) is synthesized through the chemical oxidative copolymerization of aniline, melamine, and p -phenylenediamine, and its properties are compared with those of polyaniline (PANI), poly(aniline-co- p -phenylenediamine) (PPDA 2 ), and poly(aniline-co-melamine) (PMA 4 ) hydrogels. The morphologies, mechanical properties, and chemical compositions of the hydrogels are investigated by nitrogen physisorption, rheological test, microscopic measurements, and spectroscopic techniques, while electrochemical techniques are used to evaluate their electrochemical performances. In accordance with PANI, PPDA 2 , and PMA 4 hydrogels, the PD 2 M 4 hydrogel exhibited an interconnected long nanofiber structure that encouraged the diffusion of electrolyte ions. Its double-crosslinked 3D network and high nitrogen-doping content (6.3 at. %) offered synergistic effects that generated an impressive pseudocapacitance of 657 F g −1 at 0.2 A g −1 , a superior rate capability of 72% retention at a high current density of 30 A g −1 , and good cyclic stability of 62% after 2000 charge/discharge cycles. The present work, therefore, provides a novel copolymerization strategy for N-doping and hierarchical network structure to enhance the electrochemical performances of PANI hydrogel electrodes in supercapacitor applications.