In situ gas bubble-assisted one-step synthesis of polymorphic Co3O4 nanostructures with improved electrochemical performance for lithium ion batteries

• A novel gas bubble-assisted self-assembly strategy for Co3O4 nanobowl arrays.
• Revealing the morphological evolution mechanism.
• Analysis of electrochemical properties of polymorphic Co3O4 nanostructures.
• Enhanced electrochemical activity was exhibited by nanobowl and nanotube arrays.

A novel and versatile gas bubble-assisted self-assembly technique was developed for the first-time preparation of Co3O4 nanobowl arrays by the rapid thermal decomposition of Co(NO3)2⋅6H2O on a flat substrate. The morphological modulation from novel nanobowl arrays, to nanotube arrays, to nanorods, and even to microspheres can be realized by only tuning decomposition temperature from 150 °C to 700 °C. The in situ generated (O2, H2O, NO2) bubbles guided the growth of Co3O4 nuclei, resulting in the final morphology of Co3O4 nanostructures. The Co3O4 nanostructures were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption isotherms. Analysis of electrochemical properties revealed that Co3O4 nanobowl and nanotube arrays obtained at low temperatures displayed significant enhancement of electrochemical activity because of low crystallization, small grain size, high specific surface area, and hierarchically porous structure. This simple process was applicable to large-scale production and may be extended to other materials. The porous/hollow structure and high specific surface area of the as-obtained Co3O4 nanobowl and nanotube arrays can enable their potential use in catalysis, chemical sensing, luminescence, energy storage, controlled release, and cellular applications.

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