Enhanced integration of electropolymerized poly(o-anisidine)-co-poly(o-toluidine) copolymer with reduced graphene oxide for super-capacitive performance

• POA- co -POT/rGO nanocomposite synthesized via eco-friendly electropolymerization. • Achieved high specific capacitance of 590 F g⁻¹ at 5 mV s⁻¹ in 1.0 M H₂SO₄. • Sulfuric acid enables optimal doping, conductivity, and redox reversibility vs. other acids. • Exceptional cycling stability: over 90 % capacitance retention after 500 cycles (−0.2 to 1.2 V). • Synergistic rGO-copolymer design enhances charge transfer, surface area, and stability. Conducting polymers are promising candidates for high-performance supercapacitors due to their rich redox activity, synthetic versatility, and tunable electrochemical properties. In this work, poly( o -anisidine) (POA) and its copolymer with poly( o -toluidine) (POA- co -POT) were electrodeposited onto reduced graphene oxide-coated stainless steel (rGO/SS) via cyclic voltammetry, using oxalic, phosphoric, nitric, and sulfuric acids as polymerization electrolytes. Comprehensive physicochemical characterization confirms the formation of a uniform coating composed of spherical polymer nanoparticles on rGO, along with a semi-crystalline structure, robust thermal stability, and a hierarchical porous network that facilitates rapid ion diffusion. Electrochemical evaluation in 1.0 M H₂SO₄ reveals that the POA- co -POT/rGO nanocomposite exhibits a high specific capacitance of 240 F g⁻¹ at 0.9 A g⁻¹ (from galvanostatic charge–discharge) and 590 F g⁻¹ at 5 mV s⁻¹ (from cyclic voltammetry), outstanding cycling stability (90 % capacitance retention after 500 cycles over a wide potential window of −0.2 to 1.2 V), and high Coulombic efficiency (95 %)-significantly outperforming both POA/rGO and pristine POA electrodes. This enhancement stems from the synergistic interaction between the rGO scaffold and the copolymer matrix, which collectively improve electrical conductivity, mechanical integrity, and charge-transfer kinetics, as confirmed by electrochemical impedance spectroscopy. Notably, sulfuric acid emerges as the optimal polymerization electrolyte; it's SO₄²⁻ anions enable superior doping efficiency, film homogeneity, and capacitive response-attributed to high proton mobility and anion stability during electropolymerization. The resulting POA- co -POT/rGO electrode displays hybrid electric double-layer and pseudocapacitive behavior, positioning it as a compelling architecture for next-generation supercapacitors targeting high energy and power densities. These findings highlight the potential of such nanocomposites for practical applications in advanced energy storage devices.