Niobium oxide (Nb2O5) is an interesting active material for diverse technologies ranging from catalysis and sensors to energy storage and electrochromic devices owing to its unique combination of optical, electronic, and electrochemical properties. These properties vary between different phases and morphology in the Nb2O5 system, but systematic studies that correlate properties to phase and morphology are limited by current synthetic methods, which require post-synthetic high temperature treatments and suffer from a lack of direct and precise control over morphology, crystal structure, and stoichiometry. Here, we report on a heat-up colloidal synthesis method that produces orthorhombic Nb2O5 nanorods with an aspect ratio of 1 nm in width by 31 nm in length that preferentially grow along the [001] direction. We found that the synthesis of nanorods does not proceed by aminolysis of niobium oleate, unlike conventional metal oxide nanocrystal synthesis, based on X-ray diffraction, Raman, and Fourier-transform infrared spectroscopy. Instead, the mechanism involves three distinct subsequent steps: formation of niobium oxo clusters by adding oleylamine into a niobium oleate solution, condensation into an amorphous Nb2O5 intermediate below the reaction temperature, and crystallization and growth of Nb2O5 nanorods. We investigated the electrochromic behavior of nanorod thin films upon Li+ intercalation and observed predominantly near-infrared plus modest visible modulation, fast switching kinetics, and durability for 500 charge-discharge cycles.

Electrochromic niobium oxide nanorods

2019 Fall National Meeting

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