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.