Morphology evolution of urchin-like NiCo2O4nanostructures and their applications as psuedocapacitors and photoelectrochemical cells

Abstract

Urchin-like NiCo₂O₄ nanostructures were synthesized on a large scale via a simple hydrothermal method free of any template and catalyst. As-synthesized NiCo₂O₄ urchins have uniform diameters of 5 μm with numerous small nanorods radially grown from the center. Typical nanorods have diameters of 100–200 nm and lengths of about 2 μm. Studies found that urea plays an important role to determine the morphology of the products and a “rods-to-straw-bundles-to-urchins” mechanism was proposed. With a porous structure and a large surface area of 99.3 m² g⁻¹, the prepared NiCo₂O₄ urchins exhibited superior specific capacitance of 1650 and 1348 F g⁻¹ at current densities of 1 and 15 A g⁻¹, respectively. The capacitance loss after 2000 cycles is only 9.2% at the current density of 8 A g⁻¹, indicating their excellent cycling stability. Photoelectrochemical cells were also fabricated on the urchin-like NiCo₂O₄ nanostructures with the features of fast photocurrent response and excellent stability. A high photocurrent response of about 70 μA cm⁻² was observed.