Graphene-templated growth of hollow Ni3S2 nanoparticles with enhanced pseudocapacitive performance

Abstract

Droplet-shape hollow Ni₃S₂ nanoparticles, as well as corresponding partially nickel-filled nanoparticles, of narrow diameter distribution and uniform dispersion were successfully synthesized on two-dimensional graphene templates using a facile process with moderate reaction conditions. The nanoparticle composites were examined as electrochemical supercapacitor materials for energy storage application. We found that the shape of the nanoparticles is dominantly droplet-shape, with shape complementary to graphene support, which ensures good contact between them. The height of the nanoparticles increases linearly with the diameter with a coefficient of 0.44 from the fitting results, and the average height/diameter ratio of those nanoparticles is about 0.6, evidence that the nanoparticles have strong interaction with the graphene template, partially because of graphene–nickel ion interaction which ensures good surface wetting. Such a composite of droplet-shape hollow Ni₃S₂ nanoparticles grown on reduced graphene oxides (rGOs) exhibits a high specific capacitance of 1022.8 F g⁻¹ at scanning rate of 2 mV s⁻¹, with a value of 1015.6 F g⁻¹ obtained at a discharge current density of 1 A g⁻¹. Improvement of the rate capability can be further obtained by partially filling the hollow core with nickel metal, as 93.6% of the specific capacitance is retained with this structure by increasing the discharge density from 1 A g⁻¹ to 10 A g⁻¹. Our method provides a new approach for controlling the structure of graphene-based nanocomposites, with the potential for use in high performance supercapacitor applications.