Design of anisotropic Co₃O₄ nanostructures: control of particle size, assembly, and aspect ratio

Abstract

Alignment of Co₃O₄ nanoparticles to yield a range of anisotropic nanostructures with a controlled aspect ratio (1:5 to 1:13) was possible from a single nanostructured precursor (cobalt oxalate) that was obtained by a microemulsion method under controlled kinetic parameters and the temperature of decomposition. The role of the cationic surfactant is critical for obtaining the anisotropic nanostructures of Co₃O₄ comprising an assembly of Co₃O₄ nanoparticles (diameter 5–50 nm). The shape (from spherical to highly elongated) and size of individual nanoparticles could be varied by the temperature of decomposition. Higher temperature led to elongated and larger particles. All of the nanorods showed antiferromagnetic behavior with a decrease in Neel temperature (TN) with decrease in the average size of the individual oxide nanoparticles. The variation of TN with the particle diameter follows the finite-size scaling relation. These nanostructures were found to be excellent electrocatalysts for oxygen evolution reaction (OER), with a high current density of 104 mA/cm².