Hollow core–shell nitrogen-rich graphitic carbon as electrode materials for high-energy storage capacitors

Nanostructured materials with controlled morphologies and structural textural properties are highly desirable to fabricate supercapacitor electrodes with exceptional capacitive performances. To demonstrate this concept, a cost-effective, template-free method has been developed to craft hollow hierarchical carbon structures enriched with nitrogen content. Hollow carbons derived from different zeolitic imidazolate frameworks (C H-ZIF-8, C H-ZIF-67, and C H-ZIF-8@ZIF-67) were deliberated and utilized as electrode materials for EDLCs. Remarkably, the distinctive core–shell architecture of C H-ZIF-8@ZIF-67 results in large contact areas combined with hierarchical macro-, meso- and microporous structures synergistically accelerate electrolyte diffusion through the hollow framework, thus enhancing the electron transport along the carbon skeleton. The high nitrogen content, large graphitization degree, and the residual cobalt nanoparticles (derived from H-ZIF-67) act as electroactive sites contributing to additional pseudocapacitance behavior, thus enhancing the overall capacitance. The C H-ZIF-8@ZIF-67 electrodes displayed extraordinary electrochemical capacitance performance equal to 950.5 F g⁻¹ in KOH, at 0.2 A g⁻¹, with outstanding cyclic stability (cyclic retention of 99.9 % of its initial capacitance even after 5000 cycles at 10 A g⁻¹). This strategy considers the easy, available, and new gate to construct hollow carbon materials with improved properties for energy storage applications.