Chemical reduction-induced defect-rich bismuth oxide-reduced graphene oxide anode for high-performance supercapacitors.

We prepare bismuth oxide-reduced graphene oxide (Bi2O3-rGO) composite anode using a one-step chemical precipitation/reduction method. Under a reducing atmosphere, oxygen atoms on the surface of Bi2O3 are gradually removed and neighboring oxygen atoms migrate to the surface, leaving oxygen vacancies. Defective Bi2O3 enhances the number of active sites, providing additional pseudocapacitive performance. The transition metal oxide-based Bi2O3 acts as an anode, providing capacitive performance that far exceeds that of conventional carbon materials. Moreover, the introduction of rGO forms a conductive network for Bi2O3, improving capacitive contribution and ion diffusion capabilities for the electrode. The Bi2O3-rGO-100 (GO added at 100 mg) exhibits a high specific capacitance of 1053F/g at 1 A/g, significantly higher than that of Bi2O3 (866F/g). The Bi2O3-rGO-100 anode and Ni3Co2-rGO cathode are assembled into a battery-type supercapacitor. The coin-cell device achieves an energy density of 88.2 Wh kg-1 at a power density of 850 W kg-1. The Ni3Co2-rGO//Bi2O3-rGO-100 pouch-cell device demonstrates an extremely low Rct of 0.77 Ω. At a power density of 850 W kg-1, the energy density reaches 118.5 Wh kg-1, and remains 67.4 Wh kg-1 at 8500 W kg-1.

Battery-like bismuth oxide anodes for soft-packed supercapacitors with high energy storage performance.

Bismuth compounds are of interest because of abundant reserves and high theoretical capacity for use as anodes in supercapacitors. In this work, bismuth oxycarbonate is synthesized by a hydrothermal method, and bismuth oxide is obtained by the subsequent calcination process, both of which possess high specific capacity. In particular, Bi2O3 possesses a specific capacity of 1178 F g-1 (1178 C g-1, 327 mA h g-1) at a current density of 1 A g-1, and still retains 94.9% capacity at 20 A g-1, indicating excellent rate capability. Furthermore, Ni(OH)2 is prepared with a specific capacity of 2447 F g-1 at 1 A g-1. Using Bi2O3 as the anode and Ni(OH)2 as the cathode, respectively, the soft-packed supercapacitors are assembled with a large voltage window of 1.75 V. The energy density is as high as 139.7 W h kg-1 at a power density of 874.8 W kg-1. Even at 18 000 W kg-1, the device retains an energy density of 94 W h kg-1. Connecting two devices in series as a power source can light up 88 light emitting diodes (LEDs) for 2 hours, and drive a tiny fan to run for 18 seconds. The work provides new ways for the practical application of supercapacitors.

Facile syntheses of Fe2O3-rGO and NiCo-LDH-rGO nanocomposites for high-performance electrochemical capacitors.

Faraday-type electrode materials and devices for electrochemical capacitors have been widely investigated. However, their applications are severely limited by the preparation method and cost of electrode materials. In this work, high-performance electrochemical capacitors were successfully assembled using Fe2O3-decorated reduced graphene oxide (rGO) nanocomposites and NiCo-Layered Double Hydroxides (LDH) as the anode and cathode, respectively. An easy and efficient approach (the modified precipitation method) for the large-scale fabrication was used to prepare Fe2O3 and NiCo-LDH, supported by rGO sheets, respectively. The anode material, Fe2O3-rGO, exhibited an excellent specific capacitance (Csp) of 1073 F g-1 at a current density of 1 A g-1 and a retention rate of 92 % at 10 A g-1, while the NiCo-LDH-rGO cathode material provided a Csp of 1850 F g-1 at 1 A g-1 and maintained 84 % at 10 A g-1. The effective combination of these electrodes for the NiCo-LDH-rGO//Fe2O3-rGO electrochemical capacitors resulted in an excellent energy density of 108 Wh/kg at a power density of 884 W/kg, with remarkable cycling stability (80 % after 1000 cycles at 10 A g-1). We believe that this work, including the proposed method and electrode materials, will advance the further development and commercialization of electrochemical capacitors.