Synthesis and surface engineering of carbon-modified cobalt ferrite for advanced supercapacitor electrode materials

The precise design and surface modification of electrode materials are crucial challenges for advancing the supercapacitor technology. In this study, we report a straightforward two-step process for the synthesis of a cobalt ferrite (CoFe₂O₄)/carbon hetero nanostructure. The CoFe₂O₄ nanoparticles were first synthesized using a simple chemical oxidation method, followed by carbon modification using glucose. The modified samples were calcined at 400 and 600 °C for 4 h in N₂ atmosphere to optimize the structural and electrochemical properties. The increase in the grain size of carbon modified cobalt ferrite magnetic nanoparticles (MNPs) was observed from 22 to 28 nm with post annealing temperature. The presence of carbon was confirmed by the FTIR spectroscopy, FESEM and TEM analyses. The carbon decoration on the cobalt ferrite partially showed a core–shell like morphology. The saturation magnetization of bare cobalt ferrite was observed to be 76 emu/g and the same was decreased by the surface modification with carbon. A high specific capacitance of 323 F/g was observed for the carbon-modified cobalt ferrite MNPs annealed at 600 °C. The electrochemical impedance spectroscopy (EIS) analysis demonstrated that the charge-transfer resistance (R_ct) decreased significantly in the carbon-modified CoFe₂O₄ MNPs, particularly for the sample annealed at 600 °C, with an R_ct value of 17 Ω. The carbon layer effectively enhanced conductivity and reduced the electrode/electrolyte interface, led to the improved electrochemical performance, as reflected in the enhanced specific capacitance. An improved capacitance retention of 84 % was achieved in the case of carbon-modified cobalt ferrite MNPs based electrode even after 4000 cycles. The study suggested that the prepared carbon-modified cobalt ferrite MNPs stand in the limelight as a better candidate electrode material for the electrochemical applications.