V_xO_y quantum dot-enhanced nitrogen-sulfur dual-doped hierarchical porous carbon electrodes from waste eggshell...

The weathering of rocks naturally creates abundant pore structures on their surfaces. Drawing inspiration from this, we present a simple yet effective approach-combining hydrothermal carbonization and pyrolysis carbonization-to synthesize multivalent vanadium oxide (V_xO_y) quantum dot-enhanced nitrogen- and sulfur-doped hierarchical porous carbon materials derived from waste biomass of eggshell membranes. These carbon materials, termed V_xO_y-S@CESM, are used as electrodes for supercapacitors. The results demonstrate that the multivalent V_xO_y quantum dot structure effectively increases the active sites and enhances the pseudocapacitance, particularly the pseudocapacitance associated with V⁴⁺ in the composites. The optimal V_xO_y-S@CESM sample achieves a capacitance of 355 F/g at 0.5 A/g. The flexible V_xO_y-S@CESM symmetrical supercapacitor retains more than 80 % of its capacity across various bending angles (0°-180°). It also exhibits a high energy density of 27.9 Wh kg^-1 and a power density of 906 W kg^-1. Density functional theory (DFT) calculations confirmed that the introduction of V_xO_y quantum dots significantly increases the adsorption energy of Na⁺ ions and induces polarization in the carbon materials. This quantum dot-enhanced carbon material design opens new avenues for the development of advanced energy storage materials.