Dual-surfactant-engineered FeNi₃–carbon fabric electrodes for high-performance flexible supercapacitors

Producing flexible, binder-free supercapacitor electrodes from earth-abundant alloys is challenging owing to difficulties in controlling the alloy dispersion and interfacial integration on cotton fabric. This report presents a mixed ionic surfactant-assisted strategy for growing FeNi₃ nanoparticles on cotton fabric, followed by high-temperature carbonization to produce flexible FeNi₃–carbon composite electrodes. Sodium dodecyl sulfate and cetyltrimethylammonium bromide simultaneously regulate micelle-assisted nucleation, prevent particle agglomeration, and create a conductive carbon framework. The surfactant concentration affects the electrochemical kinetics and charge-transfer performance. The optimized electrode, prepared with 2 mmol of each surfactant, delivers an areal capacitance of 1104.8 mF·cm⁻², capacitance retention of 120% after 20,000 charge–discharge cycles, and energy densities of 153.4 and 66.7 μWh·cm⁻² at power densities of 2 and 100 mW·cm⁻², respectively, with dominant surface-controlled pseudocapacitance, low charge-transfer resistance, and sub-millisecond relaxation. Its excellent durability and flexibility make it a promising material for wearable energy-storage applications.