Activating the quantum capacitance of C24 Nanocages for supercapacitors through B/N substitution and 3d transition metal doping (Sc Zn) - a DFT perspective

Supercapacitors offer high power output and long cycle life, but their limited energy density necessitates the development of novel electrode materials with enhanced quantum capacitance (C Q ) and surface charge storage (Q) capability. Hence, this study employs density functional theory (DFT) to investigate C Q , electronic structure, and Q behavior of C 24 nanocages and their B- and N- substituted derivatives (C 23 B, and C 23 N denoted as CB and CN). Unlike earlier studies on 2D carbon structures or larger fullerenes, this work provides the first systematic evaluation of the smaller C 24 nanocage as a supercapacitor electrode material. To further enhance C Q and Q performance, 3d transition metals (TMs) (Sc Zn) are introduced through doping. Structural stability is confirmed via cohesive and binding energy calculations, with Ti-doped systems being the most robust. Charge density difference maps and Bader analysis demonstrate significant charge transfer from dopant metals to the cage, while partial density of states reveal 3d-2p orbital hybridization as the origin of improved C Q . The bare C 24 , CB, and CN cages show peak C Q values of 158, 127, and 114 μF/cm 2 , respectively. Upon doping, C Q increased to 169 μF/cm 2 (C/Sc), 163 μF/cm 2 (CB/Zn), and 171 μF/cm 2 (CN/Cr). Remarkably, CN/Ti and CN/V maintain high C Q even at zero bias, an unusal behavior in carbon-based electrodes that highlights their promise for low-voltage applications. By establishing C 24 based nanocages as a previously unexplored yet tunable platform, this work provides fundamental insights into d-orbital-mediated capacitance enhancement and positions these nanostructures as strong candidates for next-generation supercapacitor electrodes.