Jahn-Teller Disproportionation Induced Exfoliation of Unit-Cell Scale ϵ-MnO.

Exfoliation of non-layered (structurally) bulk materials at the nanoscale is challenging because of the strong chemical bonds in the lattice, as opposed to the weak van der Waals (vdW) interactions in layered materials. We propose a top-down method to exfoliate ϵ-MnO nanosheets in a family of charge-ordered La AE MnO (AE=Ca, Sr, Ba) perovskites, taking advantage of the Jahn-Teller disproportionation effect of Mn and bond-strength differences. ϵ-MnO crystallized into a nickel arsenide (NiAs) structure, with a thickness of 0.91 nm, displays thermal metastability and superior water oxidation activity compared to other manganese oxides. The exfoliation mechanism involves a synergistic proton-induced Mn disproportionation and structural reconstruction. The synthetic method could also be potentially extended to the exfoliation of other two-dimensional nanosheet materials with non-layered structures.