Fig. 7: 3D XANES analysis of Co3O4 microparticles quenched after the second reduction cycle at 900 °C for 30 min, preserving the high-temperature phases.

(A) 3D volume rendering based on peak position fitting, showing lower peak position values (corresponding to the CoO phase) predominantly at the particle surface, while higher values (Co3O4 phase) remain in the interior; (B) Representative image slices in XY view from the 3D XANES data, illustrating the spatial distribution of CoO and Co3O4 phases, as well as the presence of internal/isolated and open pores, Z = 0 is defined as the bottom of the sample in z direction in (A); (C) The enlarged view in the white dash rectangle in the X-Y views in (B) at Z = 6.63 and 6.89 μm.