Synthesis of sodium cobalt oxide submicron tubules using citric acid-based sol-gel route assisted by porous aluminum oxide membrane

We report synthesis of the sodium cobalt oxide γ-Na _xCoO₂ submicron tubules using the citric acid-based sol-gel route with the assistance of commercial porous anodized aluminium oxide (AAO) membrane with a nominal pore size of 200nm as supporting templates. The y-Na_xCoO₂ submicron tubules can be obtained at 500°C using a rapid-heat-up procedure and held for 30 min. The submicron tubules have a diameter of 200-250 nm. The products are investigated using various techniques including powder x-ray diffraction, field emission scanning electron microscope and transmission electron microscope. The atomic ratio of Na/Co of they-Na _xCoO₂ submicron tubules is determined using energy dispersive x-ray spectra. The atomic ratio of Na/Co tends to be less than 0.5 due to the tendency of Na⁺ de-intercalating from its parent structure during the tubules collecting process.