Growth of MnFe 2 O 4 Nanoparticles on gC 3 N 4 Nanosheets for Enhanced Charge Storage: A Heterostructure Approach to High‐Performance Supercapacitors

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.