To verify the configuration of the sub-unit cell within rGO layers, we calculated the cohesive energy for four possible configurations by using the density functional theory (DFT) (see Methods for details). The most energetically favored configuration was obtained by relaxing both Cr2O3 as well as interlayer space and subsequent determination of the cohesive energy (Figure and Table. S7). Based on the reconstructed crystal model and our experimental observations with different synthesis duration and voltages, we can discuss insights on the process of the angstrom confined electrochemical synthesis process. In SI section 5, we discuss the formation of 2D metal oxide and the role of angstrom confinement. In line with previous studies, we suggest that the angstrom confinement results in a high-pressure environment and oxidizing environment favoring the growth of 2D metal oxide. Moreover, the occurrence of the porous network of 2D metal oxides is explained by the increasing limitation of mass transport in the rGO network with increased synthesis duration due to the suppressed swelling.