Figure 6.

a) Schematic illustration of design of the hierarchical CoO_x nanosheet/nanotube structures with multiple scale optimizations. b) SEM and c) TEM images of the hierarchical CoO_x nanosheet/nanotube structures. d) Water oxidation current of the CoO_x‐vacuum (red curve), CoO_x‐air (blue curve), IrO_x (brown curve), and CuO nanowire (black curve) at 5 mV s⁻¹. Inset: the zoom‐in plot of the onset potential region. e) Demonstration of water splitting cell powered by a 1.5‐V AAA battery. The CoO_x catalyst was loaded on Ni foam with a loading mass of 4 mg cm^–2 as an anode and a Pt‐mesh was used as a cathode. Reproduced with permission.78