Electrochromic Niobium Oxide Nanorods

Niobium oxide (Nb2O5) is an interesting active material for technologies ranging from catalysis and sensors to energy storage and electrochromic devices owing to its unique optical, electronic, and electrochemical properties. These properties vary between different phases and morphologies in the Nb2O5 system, but systematic studies that correlate properties to phase and morphology are limited by current synthetic methods, which require postsynthetic high temperature treatments and suffer from a lack of direct and precise control over morphology, crystal structure, and stoichiometry. Here, we report a heat-up colloidal synthesis method that produces orthorhombic Nb2O5 nanorods 1 nm in width by 31 nm in length that preferentially grow along the [001] direction. The synthesis is based on aminolysis of niobium oleate in octadecene, and nanorods are formed through three distinct steps: aminolysis-driven formation of niobium oxo clusters, condensation into amorphous Nb2O5 seeds below the reaction temperature (240 °C, under atmospheric pressure), and crystallization and growth of Nb2O5 nanorods. We investigated the electrochromic behavior of nanorod thin films upon Li+ intercalation and observed predominantly near-infrared coloration, fast switching kinetics, and durability for at least 500 charge–discharge cycles.