Colloidal Polymerization of Polymer-Coated Ferromagnetic Cobalt Nanoparticles into Pt-Co3O4 Nanowires

In this report, functional one-dimensional (1-D) Pt-Co3O4 heterostruc-tures with enhanced electrochemical properties were synthesized via colloidal polymerization of polymer-coated ferromagnetic cobalt nanoparticles (PS-CoNPs). Colloidal polymerization of dipolar nanoparticles into hollow metal−semiconductor nanowires was achieved via a consecutive galvanic replacement reaction between Co0 and Pt2+ precursors, followed by a nanoscale Kirkendall oxidation reaction and a calcination treatment. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-angle annular dark field scanning TEM (HAADF-STEM), and field-emission scanning electron microscopy (FESEM) revealed the structural and morphological evolution of the hollow cobalt oxide nanowires (D = 40 nm) with platinum nanoparticles (PtNPs; D ∼ 2 nm) entrapped within the growing oxide shell. Various calcination conditions were investigated via X-ray photoelectron spectroscopy (XPS) to obtain the optimal surface composition of the metallic Pt and semiconducting Co3O4 phases. Cyclic voltammetry of the 1-D Pt-Co3O4 heterostructures demonstrated a sevenfold enhancement in specific capacitance in comparison to the pristine Co3O4 nanowires. Preliminary results also showed that the calcined 1-D Pt-Co3O4 heterostructures catalytically hydrogenate methyl orange, and the rates of the hydrogenation were dependent on surface composition.