Here, we firstly report a controlled electrochemical method to obtain (sub-) unit cell thick 2D transition metal oxides, like Cr2O3, Fe2O3, by using the angstrom-confinement of stacked reduced graphene oxide (rGO) layers. The 2D holey polycrystalline network of Cr2O3 and Fe2O3 is only 4.5 Å and 5.4 Å thick respectively. The material is homogenously distributed within the 2.5 cm 2 x 500 nm rGO film. As an example of the unexpected properties of these electrochemically synthesised 2D materials, we find that the 2D form of Cr2O3 is a high performing oxygen evolution reaction (OER) catalyst, in contrast to its low performing bulk form . Although this class of 2D non-vdW materials is still vastly unexplored due to limited synthesis routes, 2D metal oxides are expected to hold a wide range of interesting properties and possible applications. With that a new and easily accessible route for obtaining sub-unit cell thick 2D metal-oxides is unlocked.