Tailoring hierarchical yolk-shelled nickel cobalt sulfide hollow cages with carbon tuning for asymmetric supercapacitors and efficient urea electrocatalysis

Abstract

Effective electrode design is necessary to drastically improve the performance and efficiency of sustainable energy conversion and storage devices. In this study, carbon decorated three-dimensional (3D) yolk-shelled nickel cobalt sulfide (NiCo2S4/C) hollow cages structure was synthesized by a simple one-pot method under solvothermal conditions in an ethylene glycol (EG) solution. The as-fabricated NiCo2S4/C hollow cages with unique porous features, a large surface area, and robust connection to electrolyte ions at the entire electrochemically active surfaces display superior performances for both charge storage and urea electrocatalysis. As a supercapacitor electrode material, the composite shows a high specific capacitance of 2362 F g−1 at a current density of 1 A g−1 and maintains around 1250 F g−1 at 50 A g−1, confirming its excellent rate capability. The established asymmetric capacitor device achieves a maximum energy density of 60.2 Wh kg−1 and a power density of 375 W kg−1 with a remarkable cycling stability over 10,000 cycles of continuous charge-discharge processes (about 87.9% capacity retention). Impressively, the NiCo2S4/C composite reveals a good capability for catalyzing urea with an improved anodic current density and long-term durability for 1000 consecutive cycles. These results indicate that the hierarchical NiCo2S4/C hybrid may hold a potential to be a practical candidate for efficient power generation.