Cobalt sulfide nanoparticles decorated on TiO2 nanotubes via thermal vapor sulfurization of conformal TiO2-coated Co(CO3)0.5(OH)·0.11H2O core–shell nanowires for energy storage applications

Abstract

Core–shell nanowires, consisting of Co(CO₃)_0.5(OH)·0.11H₂O cores (∼80 nm in diameter and ∼2 μm in length) and TiO₂ shells (∼20 nm in thickness), have been fabricated on various substrates via hydrothermal synthesis of the crystalline nanowire cores at 90 °C followed by atomic layer deposition (ALD) of the conformal amorphous shells at 25 °C. Post-growth thermal vapor sulfurization of such Co(CO₃)_0.5(OH)·0.11H₂O–TiO₂ core–shell nanowires results in hybrid nanostructures of nanotubes decorated by nanoparticles. A combination of X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy revealed that the nanotubes are anatase crystalline TiO₂ while the nanoparticles decorated on the walls of the nanotubes are dominated by Co₃S₄ crystallites. The hybrid nanostructures have been electrochemically characterized in a 2 M KOH electrolyte, they exhibit a specific capacitance of 650 F g⁻¹ at a scan rate of 10 mV s⁻¹. However, the sulfurized TiO₂ nanotubes, from which the nanowire cores were etched away in a dilute HCl (0.2 M) solution before the sulfurization, do not exhibit any apparent pseudocapacitance behaviors. They are more likely supporting templates in the hybrid nanostructures. These properties of the obtained hybrid nanostructures indicate that the cobalt sulfide nanoparticles decorated on TiO₂ nanotubes fabricated by thermal vapor sulfurization can be promising electrodes for energy storage applications.