Figure 2

Microstructure of NiCo₂O₄ single-shell and double-shell spheres. TEM images of (a) carbon spheres, (b) single-shelled and (c) double-shelled NiCo₂O₄ spheres. (d) XRD patterns of the as-prepared hollow NiCo₂O₄ spheres. High-resolution TEM images (e, f) of the sheets and corresponding SAED result.