Hierarchical Carbon Architecture Derived from Polybenzoxazine–Melamine Composites: A Strategy for High-Rate Electrochemical Performance

Developing sustainable, low-cost carbon materials for advanced energy storage remains a major challenge. This study reports the synthesis of three-dimensional (3D) hierarchical porous carbon foams using a polybenzoxazine-coated melamine sponge template, followed by carbonization at 600, 700, and 800 °C. The melamine sponge provided an interconnected porous framework, while nitrogen-rich polybenzoxazine enabled the formation of heteroatom-doped carbon structures. Structural analyses (SEM, XRD, Raman, and XPS) showed that carbonization temperature strongly influenced graphitization, pore development, and nitrogen functionalities. Among all samples, the foam carbonized at 800 °C showed the best electrochemical performance, delivering a specific capacitance of 287 F g−1 at 1 A g−1, 84% retention at 10 A g−1, and 94% capacitance retention after 10,000 cycles. Its superior behavior is attributed to the synergistic effect of improved conductivity, hierarchical porosity, and favorable nitrogen doping. These findings demonstrate that controlled carbonization is an effective strategy for designing high-performance carbon electrodes for supercapacitors, with additional potential in catalysis, adsorption, and EMI shielding.