Figure shows the crystal structure of Cr2O3, where the unit cell and (11 � 0) plane are indicated by black lines and blue plane, respectively. In case of reference Cr2O3, the measured length of the unit cell perpendicular to the (11 � 0) plane is ~11.5 Å. This exceeds the maximum thickness of Cr2O3 that is possible within the rGO nanocapillaries (4.3 Å, brown dotted lines in Figure ). Therefore, the synthesized Cr2O3 grains should be sub-unit cells as shown in Figure .