The effect of the nitric acid heat treatment time on the electrochemical properties of NiCo₂S₄/carbon cloth composites as supercapacitor electrode materials

Carbon fiber cloth (CC) was treated with nitric acid for different times, then loaded with NiCo₂S₄ nanoparticles by a one-step solvothermal method to prepare NiCo₂S₄/CC composites for use as supercapacitor electrode materials. Results show that the fiber surface became rough and the oxygen content increased with increasing acid treatment time. When the acid treatment time was 12 h, the distribution of NiCo₂S₄ nanoparticles on the carbon fiber was the most uniform among the samples investigated. The NiCo₂S₄/CC-12 h electrode achieved the highest specific capacitance of 1 298 F g^-1 at 1 A g^-1, and the capacitance remained at 89.7% of that at 1 A g^-1 when the current density was increased to 20 A g^-1. The capacitance retention rate was 95.3% after 3 000 cycles at 5 A g^-1. When the NiCo₂S₄/CC and carbon nanofibers wwere used as the positive and the negative electrodes, respectively, the supercapacitor delivered a high energy density of 37.5 W h kg^-1 at a power density of 754 W kg^-1.