Enhanced cycling stability of ZnO-doped NiCo2O4 electrodes for acidic solid-state symmetric supercapacitors

Abstract

An eco-friendly and cost-effective reflux approach is employed to synthesize ZnO-doped NiCo₂O₄ (NCOXZnO) nanocomposites for supercapacitor applications. Advanced sophisticated tools are employed to investigate the structure, surface morphology, magnetic properties, surface area, and optical characteristics of NCOXZnO nanocomposites to validate their purity. The findings revealed that doping of ZnO significantly influenced the particle size, paramagnetic behaviour, porosity, and active surface area of the pristine NCO material. Electrochemical studies show that NCO7ZnO with 7 wt% ZnO achieves optimal performance, with a specific capacitance of 293 F g⁻¹ at a specific current of 0.5 A g⁻¹ and 439 F g⁻¹ at a scan rate of 1 mV s⁻¹ in 0.5 M H₂SO₄, surpassing pristine NCO. The NCO7ZnO nanocomposite also shows a high surface area (100.755 m² g⁻¹), higher pore volume (0.148 cm³ g⁻¹), and low charge transfer resistance (R_ct = 0.68 Ω). Additionally, the symmetric supercapacitor device using NCO7ZnO has a superior specific energy of 34.35 W h kg⁻¹ at a specific power of 200 W kg⁻¹. Furthermore, it demonstrates an impressive cycle stability of 98% over 10 000 cycles, positioning ZnO-doped NiCo₂O₄ as a highly promising candidate for next-generation supercapacitors.