Application of CoFe_2 - xMn_xO₄ spinel structures as an efficient electrode material for supercapacitors

In this study, CoFe_2 - xMn_xO₄ (CMFO-x, x = 0.0, 0.2, 0.5 and 0.8) spinel materials were successfully synthesized using a combustion sol-gel method and used as electrode materials for supercapacitor. X-ray diffraction (XRD) patterns confirmed the successful formation of the spinel structure and the high purity of all samples. In addition, the results of scanning electron microscopy (SEM) showed that the samples doped with Mn cations consisted of smaller nanoparticles than the base sample (CMFO-0.0), which could increase the effective surface area and improve charge transfer. Also, a significant improvement in oxygen vacancy was observed in the CMFO-0.2 sample, which could play a key role in enhancing the electrochemical activity and pseudo-capacitive behavior of this material. In general, it can be said that partial Mnⁿ⁺ substitution improved the ionic and electronic conductivity of the spinel structure. The electrode based on CMFO-0.2 was able to provide the highest specific capacitance of 433.44 F.g^- 1 at a current density of 3 A.g^- 1. Based on electrochemical analyses, all synthesized electrode materials exhibited pseudo-capacitive behavior. Furthermore, a symmetrical cell made of CMFO-0.2 material showed an excellent energy density of 438.86 W.h.kg^- 1 at a power density of 3800 W.kg^- 1 and a constant current density of 3 A.g^- 1. Long charge-discharge cycles were used to investigate the life cycle of CMFO-0.2, and the results showed that this sample was able to maintain 92% of its initial capacitance after 5000 cycles.