Synergistic Enhancement in Energy Storage for Supercapacitors: Decoration of Biomass-Derived Carbon with Hf ₆ Ta ₂ O ₁₇ Quantum Dots

Recently, numerous researchers have overcome the insufficient energy density of metal oxides in energy storage applications by tailoring their dimensions to the quantum dot scale and integrating them with carbon-based matrices. In this work, Hf6Ta2O17 quantum dots (HTO-QDs) were synthesized in situ on the surface of biomass-derived carbon nanospheres (CNS) via a polymer-derived ceramic method, resulting in CNS@HTO-QDs composites. The influence of varying HTO-QDs content on the microstructure and energy storage performance of the composites was systematically investigated using XRD, SEM, TEM, FTIR, and an electrochemical workstation. The results indicate that the uniformly dispersed HTO-QDs on the CNS surface significantly enhance the energy storage performance of the composite. Among them, CNS@HTO-QDs-25, with the highest HTO content, exhibits the maximum specific capacitance (485.3 F g–1). Combined XPS analysis and first-principles calculations reveal that the HTO quantum dots not only contribute additional pseudocapacitance to enhance the electrochemical performance of the composite, but also provide strong interfacial interactions via the formation of M–O–C covalent bonds with the CNS matrix to improve the ion adsorption and transport capabilities of the composite material. Additionally, a symmetric supercapacitor (CNS@HTO-QDs-25||CNS@HTO-QDs-25) prepared in this study exhibits excellent specific capacitance, superior energy density, and good cycling stability, demonstrating an effective approach to the development of composites of transition metal oxides and carbon-based materials.