Construction of cobaltous oxide/nickel–iron oxide electrodes with great cycle stability and high energy density for advanced asymmetry supercapacitor

Cobaltous oxide/nickel–iron oxide (Co₃O₄/NiFe₂O₄) hybrids were fabricated via a template-free hydrothermal route with cyclodextrin as a reactor and a further two-step annealing treatment in an air atmosphere. The hybrid is composed of many small nanoparticles with a particle size distribution range from 20 to 50 nm. The hybrid combined the advantages of Co₃O₄ and NiFe₂O₄ nanoparticles, presenting enhanced electrochemical properties than its single component. The Co₃O₄/NiFe₂O₄ (0.6:1) hybrid electrode exhibited the highest specific capacitance and great electrochemical cycle stability (over 90.7% of total capacitance at 2 A g⁻¹ after 1000 cycles and still kept 84.6% at 5 A g⁻¹ after 5000 cycles). This may be ascribed to the common contribution of each component, which not only provided good electronic conductivity for efficient charge transfer but also a stable structure for better ions diffusion. A Co₃O₄/NiFe₂O₄//AC asymmetry supercapacitor was assembled and manifested the highest energy density of 76.0 Wh kg⁻¹ at a power density of 859.7 W kg⁻¹ and still kept 37.3 Wh kg⁻¹ at the highest power density of 6.0 kW kg⁻¹. This work indicated that the Co₃O₄/NiFe₂O₄ hybrid should be a potential active material for the electrochemical application.