Architectonic redox interface coupling in bilayered NiFe2O4@Co3O4 composites for asymmetric supercapacitive energy storage

The electrochemical performance of pseudocapacitive systems remains inherently constrained by interfacial charge transfer resistance and limited ion diffusion within transition metal oxide (TMO) matrices. To address these challenges, we report a bilayer-engineered Nickel ferrite and Cobalt oxide (NiFe₂O₄@Co₃O₄) (NiFe@Co) heterostructure, synthesized via sequential hydrothermal nanoflake growth and potential-controlled Co₃O₄electrodeposition, designed to optimize faradaic storage through hierarchical morphology and redox-synergistic interfaces. The NiFe₂O₄scaffold provides a robust multivalent redox matrix, while the conformal Co₃O₄overlayer augments conductivity and introduces complementary redox centers, enabling capacitive enhancement. Comprehensive structural and spectroscopic analyses confirm phase-pure, coherently coupled spinel bilayers with homogenous elemental distribution and minimal interfacial defects. The optimized NiFe@Co-20 electrode exhibits an outstanding areal capacitance of 3440 F/cm²and high OH⁻diffusion coefficients (up to 7.2 × 10⁻⁷ cm²/s), indicating rapid ionic transport. Kinetic deconvolution reveals predominant diffusion-controlled redox behavior (∼79.2 %) with capacitive overlap, indicative of a hybrid supercapattery mechanism. In a practical asymmetric pouch-type device (NiFe@Co-20//AC), the system achieves an areal energy density of 0.31 mWh/cm²with 77.43 % retention after 10,000 cycles and coulombic efficiency exceeding 91 %, affirming excellent rate capability and durability. This study establishes a scalable bilayer nanoarchitectonic strategy, wherein interfacial modulation and hierarchical design synergistically overcome intrinsic TMO limitations, offering a blueprint for high-performance asymmetric energy storage systems.