The rapid transition to sustainable energy technologies necessitates advanced electrochemical energy storage (EES) systems that can balance energy density, power density, and cycling stability. Among the diverse EES technologies, batteries provide high energy densities but often suffer from limited cycle life and slower charge–discharge rates. In contrast, supercapacitors excel in delivering high power density and long-term cycling stability, yet typically lag behind batteries in energy density. Bridging this performance gap is a major challenge and an active area of materials research. Organic macrocycles, such as phthalocyanines (Pcs), represent a promising class of electrode materials due to their π-conjugated frameworks, structural tunability, and potential pseudocapacitive contributions [1]. Both peripheral substituents and the central metal atom can significantly influence their electrochemical properties, affecting dispersion, electronic structure, and ion accessibility. In this study, we systematically evaluated the capacitive performance of three Pc-based electrodes at a fixed loading of 0.3 mg active material: (i) H₂PcIm, imidazole-substituted; (ii) H₂Pc, unsubstituted; and (iii) NiPcIm, nickel-centered imidazole-substituted. The electrodes were prepared as composites with reduced graphene oxide (RGO) and tested in aqueous 1 M H₂SO₄ using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The results confirm that peripheral functionalization and central atom coordination are decisive parameters in charge storage performance. At 0.3 mg, H₂PcIm exhibited higher capacitance and energy density (190.8 F/g, 21.2 Wh/kg) than unsubstituted H₂Pc (137.9 F/g, 15.4 Wh/kg), demonstrating the beneficial role of imidazole substituents in improving molecular dispersion and ion transport. More remarkably, NiPcIm delivered the best performance (219.7 F/g, 77.6 Wh/kg), surpassing both H₂Pc derivatives. This highlights a synergistic effect where peripheral groups and the central Ni²⁺ atom together modulate ion-accessible sites and interfacial conductivity, leading to substantially improved energy density. These findings underscore that molecular engineering of phthalocyanines, via simultaneous control of substituents and metal centers, provides an effective strategy to enhance energy and power densities in supercapacitor electrodes, thereby contributing to the broader development of advanced electrochemical energy storage technologies.