Synthesis of porous high–entropy spinel oxide (CrMnFeCoNi)₃O₄ for high–performance supercapacitors

High–entropy oxides (HEOs) are promising electrode materials for supercapacitors because of their tunable compositions and structural stability. However, conventional synthesis routes often involve the differences in metal ion diffusion rates that result in particle coarsening and agglomeration, which limit the full realization of electrochemical performance. Here, a surfactant–assisted hydrothermal method using cetyl trimethyl ammonium bromide (CTAB) as a structural template was employed to synthesize a porous (CrMnFeCoNi)₃O₄ high–entropy spinel oxide. Uniform and well–dispersed nanoparticles with abundant mesopores were obtained by adjusting the molar ratio of CTAB/metal cations (C/M). The optimized sample (C/M = 1.0) exhibited a specific capacitance of 570.6 F g −1 at 0.5 A g −1 and retained 75.36 % capacitance at 10 A g −1 . Kinetic analysis indicated that capacitive behavior dominated the charge storage process. An asymmetric supercapacitor, assembled with the produced HEO as the positive electrode and activated carbon (AC) as the negative electrode, exhibited an energy density of 54.4 Wh kg −1 at a power density of 562.4 W kg −1 , with 77.77 % capacitance after 10,000 cycles. This study demonstrates a simple and effective strategy to prepare porous HEOs used for high–performance supercapacitors.