Carbon Quantum Dot-Anchored Bismuth Oxide Composites as Potential Electrode for Lithium-Ion Battery and Supercapacitor Applications

The present investigation elucidates a simple hydrothermal method for preparing nanostructured bismuth oxide (Bi ₂ O ₃ ) and carbon quantum dot (CQD) composite using spoiled (denatured) milk-derived CQDs. The formation of the CQD-Bi ₂ O ₃ composite was confirmed by UV-vis absorption, steady-state emission, and time-resolved fluorescence spectroscopy studies. The crystal structure and chemical composition of the composite were examined by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The surface morphology and the particle size distribution of the CQD-Bi ₂ O ₃ were examined using field emission scanning electron microscope and high-resolution transmission electron microscope observations. As an anode material in lithium-ion battery, the CQD-Bi ₂ O ₃ composite exhibited good electrochemical activity and delivered a discharge capacity as high as 1500 mA h g ^-1 at 0.2C rate. The supercapacitor properties of the CQD-Bi ₂ O ₃ composite electrode revealed good reversibility and a high specific capacity of 343 C g ^-1 at 0.5 A g ^-1 in 3 M KOH. The asymmetric device constructed using the CQD-Bi ₂ O ₃ and reduced graphene oxide delivered a maximum energy density of 88 Wh kg ^-1 at a power density of 2799 W kg ^-1 , while the power density reached a highest value of 8400 W kg ^-1 at the energy density of 32 Wh kg ^-1 . The practical viability of the fabricated device is demonstrated by glowing light-emitting diodes. It is inferred that the presence of conductive carbon network has significantly increased the conductivity of the oxide matrix, thereby reducing the interfacial resistance that resulted in excellent electrochemical performances.