Investigation of hard/soft CoFe₂O₄/NiSc_0.03Fe_1.97O₄ nanocomposite for energy storage applications

The hard/soft CoFe₂O₄/(NiSc_0.03Fe_1.97O₄)_x (0 ≤ x ≤ 5) or simply (CFO-xNFSO) nanocrystals (NCs) were synthesized through sol–gel auto-combustion technique. The structural and magnetic properties of the ferrite composite NCs were explored in detail. The synthesized NCs were applied in the fabrication of supercapacitor electrodes to investigate their potential in energy storage applications. The cubic spinel ferrite phase of the NCs was verified by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HR-TEM) techniques. The NCs with different x ratios displayed smoothed magnetic hysteresis loops during magnetization at 300 and 10 K temperature. In addition, the plots of switching field distribution (SFD) indicated a single peak in dM/dH vs H plots. These findings demonstrate a good exchange-coupling in the CFO-xNFSO (0.0 ≤ x ≤ 5) magnetic NCs. The supercapacitor devices fabricated from the synthesized NCs displayed enhanced capacitance and relatively high energy density as compare to electric double-layer (EDL) (carbon-based) supercapacitors. The supercapacitor fabricated from CFO-xNFSO for x = 2 showed best performance in terms of specific capacitance with 204.4 F g⁻¹ at a scan rate of 10 mV s⁻¹. The performances of the fabricated supercapacitors were further tested for a higher potential window of 1.2 V, where a specific energy value of 33.2 Wh kg⁻¹ is achieved that is 144% enhancement from the same supercapacitor working at 0.8 V and 187% enhancement as compared to the carbon-based supercapacitor. The device also displayed excellent stability as it was tested for 5000 charge–discharge cycles.