Cationic Surfactant-Driven Evolution of NiFe2O4 Nanosheets for High-Performance Asymmetric Supercapacitors

This work explores the role of cetyltrimethylammonium bromide (CTAB) as a morphology-directing agent in the hydrothermal synthesis of NiFe2O4 electrodes for high-performance supercapacitor applications. By fine-tuning CTAB concentrations (0.5%, 1%, and 1.5%), a tunable nanosheet morphology was achieved, with the NiFe-1 sample exhibiting uniformly interconnected nanosheets that enhanced ion diffusion, charge transport, and surface redox activity. Structural and surface analyses confirmed the formation of single-phase cubic NiFe2O4 and the presence of Ni2+ and Fe3+ oxidation states. Electrochemical characterization in a 2 M KOH electrolyte revealed that the NiFe-1 electrode achieved an areal capacitance of 8.21 F/cm2 at 20 mA/cm2, with an energy density of 0.34 mWh/cm2 and a power density of 5.5 mW/cm2. The electrode retained 79.61% of its capacitance after 10,000 cycles, demonstrating excellent stability. An asymmetric pouch-type supercapacitor device (APSD), assembled using NiFe-1 and activated carbon, exhibited an areal capacitance of 1.215 F/cm2 and delivered an energy density of 0.285 mWh/cm2 at a power density of 6.5 mW/cm2 across a wide 0-1.8 V voltage window. These results confirm that CTAB-assisted nanostructuring significantly improves the electrochemical performance of NiFe2O4 electrodes, offering a scalable and effective approach for next-generation energy storage applications.