Theoretical and Experimental Insights of Magnesium-doped Cobalt Ferrites for Supercapacitor Applications

Abstract

In the present study, we synthesize magnesium-doped cobalt ferrite (Co0.75Mg0.25Fe2O4) nanoparticles as stable and high-performance electrodes for supercapacitor application via the sol-gel combustion method and anneal them at 200°C (MCF1), 300°C (MCF2), and 500°C (MCF3). Experimental and density functional theory (DFT) simulations of Co0.75Mg0.25Fe2O4 nanoparticles affirm a normal spinel cubic structure with partial tetrahedral occupancy and lattice expansion (8.3524 to 8.3704 Å) with subsequent temperature rise. The partial occupancies curtail the charge diffusion path length and favor a pronounced energy storage capacity. Morphological assessment also verifies the clustered and homogenous normal spinel cubic structure. Such cationic ordering increases the electronic bandgap (0.84 eV → 1.57 eV) with d-orbital splitting due to crystal field effects. However, a non-linear impact upon the optical bandgap (1.214 eV to 1.212 eV (MCF1 to MCF2) and increases to 1.22 eV (MCF3)) is the consequence of bond dissociations favoring adequate e-h charge separations at elevated temperatures. Our experimental outcomes reveal a high specific capacitance of 579.3 Fg−1 for MCF3 at 0.5 Ag−1 with a cyclic stability of 96.49% after 1000 cycles at 5 Ag−1.