Effect of synthesis routes on electrochemical properties as supercapacitor electrode for novel spinel ( CuNiFeMnCo ) 3O4 high entropy oxide

The aim of the present study is to investigate the effect of synthesis routes on phase evolution, microstructure, change in ionic state and their co‐relation with electrochemical charge storage, and magnetic properties of novel (CuNiFeMnCo)3O4 high entropy spinel oxide (HESO). We successfully synthesized novel (CuNiFeMnCo)3O4 HESO through two different synthesis methods, that is, sol‐gel and reverse coprecipitation methods abbreviated as SA‐1 and SA‐2, respectively. The XRD analysis for both samples reveals the formation of inverse spinel phase (space group Fd‐3m) with the lattice constant of 8.3602 and 8.2502 Å for SA‐1 and SA‐2, respectively. The sample synthesized through the sol‐gel method possessed porous morphology, whereas the sample synthesized through the reverse coprecipitation method had spherical particles. The x‐ray photoelectron spectroscopy confirmed the presence of +2 and +3 ionic states for Fe, Ni, and Co, while Cu has a + 2 state and Mn exist in +3 and +4 states for both the synthesized samples. The ionic states of all cations remain invariant irrespective of the synthesis methods. However, the concentration of oxygen vacancy is significantly different for samples synthesized through different routes. Both the HESO electrodes show the electrochemical double‐layer capacitive type behavior in 2 M KOH electrolytic solution. The value of maximum specific capacitance is 38.46 and 34.24 F/g at a scan rate of 5 mV/s for SA‐1 and SA‐2, respectively. Moreover, the electrodes have capacity retention of 90 and 99% for 1000 cycles at a scan rate of 50 mV/s for SA‐1 and SA‐2, respectively. The magnetic property of the synthesized HESO samples was also investigated, and the found values of magnetization and coercivity are 1.79 emu/g and 54.9 Oe and 8.5 emu/g and 67.69 Oe for SA‐1 and SA‐2, respectively.