Hierarchical Ag/N-Doped ZnO Nanowire/ZnFe2O4 Hybrid Electrodes for High-Performance Flexible Solid-State Supercapacitors

Flexible solid-state supercapacitors are attractive for wearable and compact electronics due to their mechanical compliance and operational safety. This study comprehensively investigated ZnO and Ag/N-doped ZnO nanowires prepared using a cost-effective synthesis approach. The doped ZnO was subsequently integrated with sol–gel-derived ZnFe2O4 to construct a hierarchical hybrid electrode for gel-electrolyte-based energy storage. The resultant ZnO:(Ag,N)/ZnFe2O4 nanocomposite demonstrates an areal capacitance of 67.7 mF cm–2 at 5 mV s–1, while maintaining stable operation across an extended potential window of 0–2.0 V. This enhanced charge-storage capability stems primarily from the synergistic interaction between the improved electrical conductivity imparted by ZnO:(Ag,N) and the effective Faradaic redox behavior introduced by ZnFe2O4. Dunn’s analysis indicates that charge storage is predominantly diffusion-controlled at low scan rates, while surface capacitive contributions increase at higher scan rates. The device retains 91.4% of its initial capacitance with 95.6% Coulombic efficiency after 10,000 cycles at 600 μA cm–2 and maintains stable electrochemical behavior under mechanical bending. These results demonstrate the potential of the hierarchical ZnO-based composite for flexible solid-state energy-storage applications.