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The present investigation aims to synthesize a novel (AlCuCoFeMnNi)3O4 type high entropy spinel oxide through the sol‐gel and investigate the effect of different carbon‐based additives on charge storage performance. The formation of the inverse spinel phase of [B(AB)O4] type inverse spinel phase was confirmed through the detailed x‐ray diffraction analysis of the synthesized sample. The synthesized spinel phase was indexed with the space group of Fd−3m and has a lattice parameter of 8.2697 Å. The synthesized high entropy oxide (HEO) phase Ni, Co, and Fe coexists in +2 and +3 states. At the same time, Cu in +2 state, Al in +3 state, and Mn in +3 and +4 states confirmed through x‐ray photoelectron spectroscopy. The electrochemical charge storage performance of synthesized HEO was measured through the three‐electrode setup in 2 M KOH aqueous electrolyte solution in two different potential windows, such as −0.2 to 0.4 V and 0.0 to 0.5 V. Different carbon‐based conducting materials such as acetylene black, reduced graphene oxide (RGO), and carbon particles obtained from 10‐hour ball‐milling of used dry cell carbon electrode (CP). The charge storage mechanism changes from electrochemical double layer capacitance to pseudocapacitive type as the potential window varies from −0.2 to 0.4 to 0 to 0.5 V. The value of specific capacitance for an electrode made of HEO with acetylene black, RGO, and CP was found to be 32.67, 7.50, and 4.58 F/g and 30.68, 16.33, and 9.05 F/g in the potential window of −0.2 to 0.4 V and 0 to 0.5 V at a scan rate of 5 mV/s, respectively. The cyclic performance of the developed three electrodes was measured at a scan rate of 100 mV/s for 1000 cycles, and it was found to be 94%, 98%, and 99% for electrodes made of HEO with acetylene black, RGO, and CP, respectively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The novel (CuNiZnAlFe)3O4 type nanocrystalline High Entropy Oxide (HEO) was synthesized through the sol‐gel method with combustion at 350°C for 1 h duration. The XRD analysis reveals the formation of inverse spinel [B(AB)O4] type phase indexed with the space group of Fd‐3 m confirmed through the Rietveld Refinement of the XRD data. The lattice constant for the synthesized spinel phase was found to be 8.2453°A. The Scanning Electron Microscope of the synthesized HEO confirms the flakes‐like morphology with porous microstructure. The Energy Dispersive X‐ray (EDX) analysis and elemental mapping confirm the homogeneous distribution of the cations over the selected region. It was found that Fe and Ni are in the +3 and +2 states, other cations, Cu and Zn, are in the +2 states, and Al is in the +3 confirmed through the X‐ray photoelectron Spectroscopy. The electrochemical performance was studied in three electrodes in a 2 M KOH aqueous electrolyte. The specific capacitance value was 2.02, 1.58, 1.24, 1.06, 0.87, 0.71, and 0.65 F/g at scan rates of 5, 10, 20, 30, 50, 80, and 100 mV/s, respectively. The low value of specific capacitance was observed due to the stable ionic structure of the inverse spinel phase. The magnetization behavior of the sample is also investigated. The M‐H loop of the (CuNiZnAlFe)3O4 HEO sample exhibits a ferrimagnetic nature. [ABSTRACT FROM AUTHOR]