Iron Oxide Quantum Dots‐Modified Biomass Carbon: Enabling High‐Performance Supercapacitors

Abstract Supercapacitors (SCs) are important for energy storage due to their high power density, rapid charge–discharge, and long cycle life. However, their constrained energy density limits practical deployment in long‐duration energy storage systems. To overcome this challenge, iron oxide quantum dots (FeO _x QDs) are strategically employed to leverage their pronounced quantum size effects, which enhance charge transfer kinetics and create abundant electrochemically active sites. Meanwhile, utilizing the natural hierarchical porosity and oxygen‐rich functional groups of biomass‐derived carbon materials can offer a sustainable platform. In this study, the FeO _x QDs with silk fibroin (SF) composites are prepared as electrode materials for SCs. The combination of FeO _x QDs/SF offers a strategic approach to exploiting unique properties of components synergistically. The relatively low electrical conductivity of biomass carbon is modified by the quantum size effect of FeO _x QDs, while the biomass carbon material provides a stable scaffold for the QDs, effectively inhibiting their agglomeration. Finally, the assembled pouch FeO _x QDs/SF//FeO _x QDs/SF symmetric supercapacitor (SSC) can reach an energy density of 45.13 Wh kg ⁻¹ at a power density of 1.07 kW kg ⁻¹ . In addition, its specific capacitance retention rate is 85.19% after 10000 cycles, indicating its great potential in high‐performance supercapacitor applications.