α-Bi2O3 tubular rods coated on Bi2O2CO3 nanosheets for high-performance asymmetric supercapacitor applications

Mixed phases of bismuth oxide nanostructures as an active electrode material in supercapacitor applications have recently gained huge research interest. In this study, the layered Bi₂O₂CO₃ nanosheets and the secondary phase of α-Bi₂O₃ tubular rods named Bi₂O₂CO₃/α-Bi₂O₃ heterostructure have been synthesized and utilized for supercapacitor applications. The crystal nature and microstructure of the Bi₂O₂CO₃/α-Bi₂O₃ heterostructure were initially confirmed by powder X-ray diffraction (p-XRD), Raman, UV-Vis diffuse reflectance spectroscopy (UV-DRS, absorbance), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies. X-ray photoelectron spectroscopy (XPS) measurements have investigated the oxidation states and chemical binding energies. Regarding the electrochemical performances, the Bi₂O₂CO₃/α-Bi₂O₃ heterostructure as electro-active material delivered a maximum specific capacitance (C_s) value of 635 F g⁻¹ at the given current density value of 1 A g⁻¹ in a conventional three-electrode mode. A coin cell type electrode has been fabricated using Bi₂O₂CO₃/α-Bi₂O₃ heterostructure, resulting in an asymmetric supercapacitor device cell (ASC), which has a C_s of 112 F g^{− 1} (at 1 A g^{− 1}) and a power density and energy density values of 515 W kg⁻¹ and 22.5 Wh kg⁻¹ respectively. The two supercapacitor electrodes in sequence effectively ignite the red-light-emitting diode (LED). Moreover, in the ASC type Bi₂O₂CO₃ /α-Bi₂O₃ heterostructure, the specific capacitance value was slightly reduced to 12.3 % by 2000 cycles, showing favourable cyclic performance and stability during the electrochemical process. Based on the above-mentioned characterization, the appropriate electrochemical performances of Bi₂O₂CO₃/α-Bi₂O₃ tubular rod heterostructures make them a promising candidate for future energy storage devices.