It is thus instructive to calculate the available space within the nanocapillaries of rGO based on the measured interlayer distance to estimate the maximum thickness of Cr2O3. The interlayer space measured by XRD in Figure is equivalent to the distance between the center of two carbon atoms in adjacent rGO layer. By subtracting the doubled vdW radius of carbon atoms (3.4 Å) from the interlayer distance of the dry rGO (7.7 Å), the available space between adjacent rGO sheets was estimated as ~4.3 Å. This is equivalent to the maximum thickness of Cr2O3, as the Cr2O3 within rGO sheets must be thinner than the available space within the nanocapillaries. The available space for synthesis of Cr2O3 is estimated from the wet interlayer distance of rGO as ~5.5 Å and 4.8 Å for durations < 5 min and > 5 min respectively. Interestingly, the dry interlayer space of Cr2O3/rGO is 7.7 Å and only ~0.5 Å smaller than the wet interlayer space for synthesis durations >5 min. This value of ~0.5 Å is well below the thickness of an aqueous electrolyte monolayer. This indicates interesting consequences for the synthesis procedure which are discussed in detail in SI section 5.