Hydrothermal synthesis and electrochemical capacitor application of urchin-like NiCo₂O₄ particles: effect of urea concentrations

Abstract

NiCo₂O₄-based materials are promising for high-performance energy storage materials. Here, we report the synthesis of urchin-like NiCo₂O₄ particles via the hydrothermal urea precipitation process, and studied the effect of urea concentrations on phase purity, microstructure, and electrochemical capacitor performance. NiCl₂·6H₂O, CoCl₂·6H₂O and urea, were weighed as Ni:Co:urea = 1:2:[5, 10 or 15] in molar fraction, and they were dissolved in distilled water and hydrothermally heated at 140°C for 6 h. The three precursors were calcined at 350°C for 3 h in air atmosphere. The three products were mainly composed of 3–10 µm sized urchin-like particles. All the final samples had 5–20 nm sized mesopores and ∼50–70 m²/g of specific surface area, but the distributions of Ni and Co in the urchin-like particles were affected by the starting urea concentration. The sample of single-phase NiCo₂O₄ from Ni:Co:urea = 1:2:15 showed the best electrochemical capacitor performance among the three urea concentrations.