High-performance spinel ferrites for supercapacitors: Solvothermal synthesis and electrochemical evaluation

Supercapacitors (SCs) are critical for sustainable energy storage due to their high power density and rapid charge-discharge capabilities, making them essential for renewable energy integration and electric vehicle applications. This study explores the solvothermal synthesis of spinel ferrites XFe 2 O 4 (X = Mn, Co, Ni) as electrode materials for SCs. Structural characterization through X-ray diffraction confirmed phase-pure cubic structures with lattice parameters of 0.851 nm (MnFe 2 O 4 ), 0.839 nm (CoFe 2 O 4 ), and 0.834 nm (NiFe 2 O₄), and crystallite sizes of 13.72 nm, 20.72 nm, and 11.86 nm, respectively. Scanning electron microscopy revealed agglomerated nanoparticles for MnFe 2 O 4 and CoFe 2 O 4 , and densely packed aggregates for NiFe 2 O 4 . Fourier-transform infrared spectroscopy identified a conductive carbonaceous layer from residual ethylene glycol, while UV-Vis spectroscopy determined bandgaps of 2.7 eV (CoFe 2 O 4 ), 3.12 eV (MnFe 2 O 4 ), and 3.7 eV (NiFe 2 O 4 ). Electrochemical assessments using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy showed CoFe 2 O 4 achieving a specific capacitance of 1518 F/g at 0.5 A/g with 99.9% retention after 5000 cycles, outperforming MnFe 2 O 4 and NiFe 2 O 4 . Symmetric devices based on CoFe 2 O 4 delivered a specific capacitance of 668 F/g at 1 A/g, an energy density of 33.38 Wh/kg, and a power density of 150 W/kg. These results position CoFe 2 O 4 as a promising material for next-generation SCs, advancing energy storage for sustainable systems. • Solvothermal XFe 2 O 4 (X = Co, Mn, Ni) shows phase-pure cubic spinel structures. • CoFe 2 O 4 achieves 1518 F/g and 75.92 Wh/kg – highest among XFe 2 O 4 variants. • Low Rct (887.7 Ω) demonstrates fast ion diffusion in CoFe 2 O 4 electrodes. • Symmetric CoFe 2 O 4 device exhibits 668 F/g, 99.99% stability, 99.3% efficiency (5k). • Cation selection (Co/Mn/Ni) tunes spinel ferrites for supercapacitors.