Topotactic conversion route to mesoporous quasi-single-crystalline Co ₃O₄ nanobelts with optimizable electrochemical performance

The growth of mesoporous quasi-single-crystalline Co₃O ₄ nanobelts by topotactic chemical transformation from α-Co(OH)₂ nanobelts is realized. During the topotactic transformation process, the primary α-Co(OH)₂ nanobelt frameworks can be preserved. The phases, crystal structures, morphologies, and growth behavior of both the precursory and resultant products are characterized by powder X-ray diffraction (XRD), electron microscopy-scanning electron (SEM) and transmission electron (TEM) microscopy, and selected area electron diffraction (SAED). Detailed investigation of the formation mechanism of the porous Co₃O₄ nanobelts indicates topotactic nucleation and oriented growth of textured spinel Co₃O₄ nanowalls (nanoparticles) inside the nanobelts. Co₃O₄ nanocrystals prefer [0001] epitaxial growth direction of hexagonal α-Co(OH)₂ nanobelts due to the structural matching of [0001] α-Co(OH) ₂//[111] Co₃O₄. The surface-areas and pore sizes of the spinel Co₃O₄ products can be tuned through heat treatment of α-Co(OH)₂ precursors at different temperatures. The plvanostatic cycling measurement of the Co₃O ₄ products indicates that their charge-discharge performance can be optimized. In the voltage range of 0.0-3.0 V versus Li⁺/Li at 40 mA g^-1, reversible capacities of a sample consisting of mesoporous quasi-single-crystalline Co₃O₄ nanobelts can reach up to 1400 mA h g^-1, much larger than the theoretical capacity of bulk Co₃O₄ (892 mA h g^-1).