Fig. 1. (a) Schematic illustration of the synthesis procedure of M-Co₃O₄ and M-Co₃O_4–x samples, (b) XRD patterns, (c) N₂ sorption isotherms and pore size distributions (PSDs) of M-Co₃O₄ and M-Co₃O_4–x. (d, e and f) SEM, TEM and HRTEM images of M-Co₃O_4–x; (g) high-angle annular dark-field scanning TEM (HAADF-STEM) of M-Co₃O_4–x and its corresponding elemental color mapping for Co, O and P.