A hybrid electrochemical energy storage device assembled with faradaic Bi ₂ O ₃ and MnO ₂ electrodes exhibits superior electrochemical performance with a high energy density of 79 W h kg ⁻¹ at a power density of 702 W kg ⁻¹ .

In this work, we report the synthesis of a Bi₂O₃-MnO₂ nanocomposite as an electrochemical supercapacitor (ES) electrode via a simple, low-cost, eco-friendly, and low-temperature solid-state chemical process followed by air annealing. This as-synthesized nanocomposite was initially examined in terms of its structure, morphology, phase purity, and surface area using different analytical techniques and thereafter subjected to electrochemical measurements. Its electrochemical performance demonstrated excellent supercapacitive properties in a wide potential window. Its specific capacitance was able to reach 161 F g⁻¹ at a current density of 1A g⁻¹ and then showed a superior rate capability up to 10 A g⁻¹. Furthermore, it demonstrated promising cycling stability at 5 A g⁻¹ with 95% retention even after 10,000 charge–discharge cycles in a wide potential window of 1.3 V, evidencing the synergistic impact of both Bi₂O₃ and MnO₂ in the Bi₂O₃-MnO₂ ES electrode. Additionally, the practical reliability of the envisioned electrode was ascertained by the fabrication of a symmetric Bi₂O₃-MnO₂//Bi₂O₃-MnO₂ pencil-type supercapacitor device that displayed an energy density of 18.4 Wh kg⁻¹ at a power density of 600 W kg⁻¹ and a substantial cyclic stability up to 5000 cycles. Subsequently, an LED was also powered at its full brightness using three of these devices connected in series in order to demonstrate the real-time application of the Bi₂O₃-MnO₂ ES electrode.