Facile preparation of novel and active 2D nanosheets from non-layered and traditionally non-exfoliable earth-abundant materials

Abstract

Ultrathin two-dimensional (2D) materials are emerging as a promising platform for next-generation applications in catalysis, energy storage and many engineering fields. 2D non-layered nanomaterials with abundant dangling bonds and unsaturated coordination sites possess excellent characteristics and functionalities. However, 2D non-layered nanosheets have long been considered inaccessible by exfoliation due to the absence of anisotropy in the 3D bonding network. In this work, we have successfully exfoliated earth-abundant non-layered materials (e.g., goethite, galena and calcite) to atomically thin sheets and discovered that the orientations of the exfoliated nanosheets coincide with the cleavage orientations of pristine materials, for the first time, revealing the close correlation between the accessibility of 2D nanomaterials and the existence of cleavage planes. Cleavage plane-oriented exfoliation is achieved via anisotropic in- and out-of-plane bonding, based on which a class of non-layered metal oxides, sulfides and carbonates are exfoliated to access 2D nanomaterials. The as-fabricated ultrathin and surfactant-free 2D non-layered CoOOH exhibits a very low overpotential (245 mV at a current density of 10 mA cm⁻²) for the oxygen evolution reaction (OER), which is competitive to benchmark electrocatalysts, including synthetic CoOOH nanosheets. This work deciphers the atomic correlation of 2D-bulk orientation of non-layered materials, which provides a general approach for producing traditionally inaccessible 2D nanosheets with intriguing properties and functionalities for a variety of energy and other applications.