Angstrom-confined electrochemical synthesis of non van der Waals 2D metal oxides

Materials in 2-dimensional (2D) form show remarkable properties and unexplored scientific phenomena compared to their bulk form. Layered, van der Waals (vdW) materials have an obvious 2D structure, whereas non-vdW materials have no preference to obtain 2D form. This limits the number of currently available 2D non-vDW materials. Here, we introduce a straightforward electrochemical method utilizing the angstrom-confinement of laminar reduced graphene oxide (rGO) nanochannels to obtain a porous polycrystalline network of 2D transition metal oxides (2D-TMO), a class of non-vdW materials. During synthesis the angstrom-confinement provides a thickness limitation, forcing sub-unit cell growth of 2D-TMO with oxygen and metal vacancies. We showcase that Cr2O3, a material without significant catalytic activity for OER in bulk form, can be activated as a high-performing catalyst if synthesized in the 2D sub-unit cell form. Our approach creates a strategy for combining the high activity of 2D form and high stability and robustness of bulk form. Our accessible method for obtaining 2D-TMO holds high promise to yield exciting properties for fundamental science and applications.