Relationship Between Electrical Conductivity and Supercapacitor Properties of Co3O4 Nanofibers Fabricated by Electrospinning

Abstract

Co₃O₄ with a spinel structure has been utilized as supercapacitor materials due to their active surface sites, strong absorption capacity, excellent electrochemical activity, and stability. In this study, we tried to explore the optimized electrospinning conditions, including heat-treatment temperature for Co₃O₄ nanofiber fabrication for supercapacitor applications. The X-ray diffraction patterns of Co₃O₄ nanofibers annealed at 600 and 800 ºC showed a cubic spinel crystal structure without a secondary phase, but CoO was found in the specimens annealed at 400 ºC. From the XPS curve fitting, Co³⁺ increased in the Co³⁺/Co²⁺ ratio with increasing heat-treatment temperature. The electrical conductivity of the Co₃O₄ nanofibers heated at 400, 600, and 800 ºC is 7.53 × 10⁻³, 1.12 × 10⁻², and 6.26 × 10⁻³ Ω⁻¹ cm⁻¹, respectively. The Co₃O₄ nanofibers heat treated at 600 ºC showed the highest conductivity value, and the conduction mechanism was polaron hopping between Co³⁺ and Co²⁺. The supercapacitor properties of Co₃O₄ nanofibers are evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance measurement using a three-electrode system in a 3 M KOH electrolyte. The GCD tests showed that the Co₃O₄ nanofibers heated at 600 ºC had the highest specific capacitance of 579.66 F/g. From the electrochemical impedance measurements, the charge transfer resistance (R_ct) of calcined Co₃O₄ nanofibers at 600 ºC showed the lowest value of 1.27 Ω. Also, the Co₃O₄ nanofiber exhibits excellent cycle stability with capacitance retention over 99% until 1000 cycles at a current density of 2 A/g. Therefore, the excellent supercapacitor performance of Co₃O₄ nanofibers annealed at 600 ºC is due to its nanofiber structure without a secondary phase providing a larger surface area and charge transfer.

Graphical Abstract