The fact that the dry interlayer distance undergoes no changes after the electrochemical process is surprising as the observed reduction of GO should lead to a decrease in interlayer distance. Additionally, if Cr2O3 is synthesized within the interlayer space one would expect the interlayer space to increase. Both facts can be explained with the following hypothesis: The Cr2O3 created inside the nanocapillaries of rGO fits well inside the interlayer space as angstrom confinement of the nanocapillaries limits the maximum thickness of the metal oxide. This limitation may be further ensured by the high pressure inside the nanocapillaries (> 1 GPa). . At the same time the grown material prevents the interlayer distance from becoming smaller as usually observed in rGO. The synthesis procedure is discussed in more detail in section SI 5