In-situ sulfurization of Bi2Fe4O9/Bi25FeO40 electrode for high-performance supercapacitors

Abstract

Poor conductivity limited the widespread application of metal oxide electrodes in the supercapacitors. High conductive metal sulfides facilitated the rapid ionic/electronic transfer and accelerated the reaction kinetics. Herein, a series of sulfurized Bi₂Fe₄O₉/Bi₂₅FeO₄₀ composites —-Bi₂Fe₄O₉/Bi₂₅FeO₄₀/x%Bi₂S₃ (x = 0, 8, 16, 30) were synthesized and optimized with Bi₂O_3, Fe₂O₃ and S as the raw materials by solid phase reaction. The as-prepared Bi₂Fe₄O₉/Bi₂₅FeO₄₀/x%Bi₂S₃ (x = 0, 8, 16, 30) powders appeared as the irregular particles with the sizes of 0.78–4.27 μm. Desirably, when x was 16, Bi₂Fe₄O₉/Bi₂₅FeO₄₀/16%Bi₂S₃ electrode exhibited a specific capacitance of 597.0 F/g and 132.5 F/g at 1.0 A/g in the three-electrode and two-electrode systems respectively, much higher than those of Bi₂Fe₄O₉/Bi₂₅FeO₄₀/x%Bi₂S₃ (x = 0, 8, 30). Furthermore, the corresponding energy density was 73.6 Wh/kg at the power density of 999.8 W/kg and the capacity retention was 89.7% after 2000 cycles at 2.0 A/g. The joint contributions of high conductivity and low theory capacitance of Bi₂S₃ phase may be responsible for the desirable high capacitance of optimal Bi₂Fe₄O₉/Bi₂₅FeO₄₀/16%Bi₂S₃ electrode.