Fig. 3: HRTEM images of various catalysts.

a HRTEM images of selected catalysts (unreduced Co₃O₄, Co₃O₄-200, Co₃O₄-250 and Co₃O₄-300); b representative HRTEM images of Co₃O₄-250. The HRTEM images of Co₃O₄-250 clearly show the closed shell of CoO, with the thickness of 2–3 nm and CoO(111), CoO(200) dominated.