High-performance spinel ferrites for supercapacitors: Solvothermal synthesis and electrochemical evaluation
Naeem Ullah, Tufail Ahmad, Aziz Ullah, Sufaid Khan, Muhammad Nafees, Mehboob Ali, Yousra Noor, Fawad Ahmad Khan, Baseena Sardar, M. B. Khan
Abstract
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.