Thermally engineered cationic defects in MOF-derived inverse spinel Al8[Fe16-xMnx]O32 for high-energy hybrid supercapacitors

A novel thermal strategy precisely tailors Mn-based cationic defects in MOF-derived inverse spinel Al 8 Fe 16 O 32 embedded within partially graphitized carbon. This defect engineering greatly enhances electrical conductivity, ion transport, redox activity, and structural stability. As supported through XRD, HR-TEM/STEM mapping, XPS, and XAS (XANES/EXAFS), elevated temperatures and extended soak times promote cation mobility, antisite exchange, vacancy equilibration, and phase transitions. Further, due to enriched Fe/Mn defect sites and enhanced redox/pseudo capacitance behaviour, the defective MnO x -(Al 8 )[Fe 16-x Mn x ]O 32 @AHGC electrode demonstrates a much higher specific capacitance (96 F g −1 ) than pristine Al 8 Fe 16 O 32 @AHGC (12.7 F g −1 ). The assembled HSC device AC // MnO x -(Al 8 )[Fe 16-x Mn x ]O 32 @AHGC delivers 78 % rate capability, an energy density of 25.4 Wh kg −1 (∼ 40 % higher than that of pristine), and 89 % capacitance retention after 10,000 GCD cycles at 7.5 A g −1 . This work highlights the potential of defect engineering in inverse spinel oxides combined with MOF-derived hierarchical partially graphitized carbon for advancing next-generation energy storage systems.