Growth of MnFe ₂ O ₄ Nanoparticles on gC ₃ N ₄

The development of electrode materials with high specific capacitance, excellent rate capability, and long‐term cycling stability is essential for advancing next‐generation electrochemical energy‐storage devices. In this work, MnFe ₂ O ₄ –gC ₃ N ₄ heterostructures containing different gC ₃ N ₄ loadings were synthesized through a facile solvothermal route to exploit the synergistic interaction between pseudocapacitive MnFe ₂ O ₄ nanoparticles and two‐dimensional gC ₃ N ₄ nanosheets. Electrochemical investigations revealed that the incorporation of gC ₃ N ₄ significantly enhanced the charge‐storage behavior compared with pure MnFe ₂ O ₄ . Among the prepared materials, the 70MnF–30gC ₃ N ₄ heterostructure exhibited the best electrochemical performance, delivering a high specific capacitance ( C _s ) of 701.8 F g ⁻¹ at 1 A g ⁻¹ , substantially exceeding that of other composites. Furthermore, a flexible all‐solid‐state supercapacitor device was assembled using the optimized heterostructure and tea‐waste‐derived porous carbon, which delivered an energy density of 89.3 Wh kg ⁻¹ and retained ~96% of its initial capacitance after 5000 charge–discharge cycles while maintaining excellent electrochemical performance under bending and twisting conditions. These findings demonstrate that MnFe ₂ O ₄ –gC ₃ N ₄ heterostructures are promising electrode materials for flexible and high‐performance supercapacitor applications.