Direct Formation of 2D-MnO_x under Conditions of Water Oxidation Catalysis

We describe the synthesis and characterization of a novel 2D-MnO_x material using a combination of HR-TEM, XAS, XRD, and reactivity measurements. The ease with which the 2D material can be made and the conditions under which it can be made implies that water oxidation catalysts previously described as "birnessite-like" (3D) may be better thought of as 2D materials with very limited layer stacking. The distinction between the materials as being "birnessite-like" and "2D" is important because it impacts on our understanding of the function of these materials in the environment and as catalysts. The 2D-MnO_x material is noted to be a substantially stronger chemical oxidant than previously noted for other birnessite-like manganese oxides. The material is shown to both "directly" and "catalytically" oxidize water in the presence of Ce⁴⁺, and to directly oxidize H₂O₂ in the absence of any other oxidant.