Exploring the Potential of Strontium Substituted High-Entropy Oxides for Supercapacitors and Photocatalytic...

High-entropy oxides (HEOs) have emerged as a promising class of multicomponent ceramic materials, with exceptional tunability in both structural and functional properties, due to their configurational entropy-driven stabilization. Herein, we report the synthesis of a novel rocksalt-structured (CuZnNiCoSr)O HEO prepared via reverse coprecipitation method. Rietveld refinement of powder X-ray diffraction confirmed the formation of a phase-pure rocksalt structure (Fm3̅m, a = 4.24(4) Å). X-ray photoelectron spectroscopy (XPS) revealed multiple redox-active species (Ni²⁺/Ni³⁺, Co²⁺/Co³⁺) and abundant oxygen vacancies which contributed to enhanced catalytic performance. The electrode achieved a specific capacitance of 298.67 F g^-1 at 1 A g^-1 and good cycling stability with 96.36% retention after 1000 cycles. The optical bandgap decreased from 3.72 eV at 1073 K to 1.66 eV at 1473 K, showing a clear dependence on the calcination temperature. In addition, (CuZnNiCoSr)O showed exceptional photocatalytic activity, degrading methylene blue (MB) by 97.39% in 60 min, with a rate constant of 0.03551 min^-1, following pseudo first-order kinetics. These results provide valuable insights into the rational design of HEOs and highlight (CuZnNiCoSr)O as a multifunctional material with great potential for energy storage and environmental remediation applications.