Two-dimensional heterostructures built from ultrathin CeO nanosheet surface-coordinated and confined metal-organic frameworks with enhanced stability and catalytic performance.

Two-dimensional (2D) metal-organic framework (MOF) based heterostructures will be greatly advantageous to enhance catalytic performance because they increase the contact surface and charge transfer. Herein, a novel 2D heterostructure named CeO@NiFe-MOFs, in which monolayer NiFe-MOFs is coordinated with ceria (CeO) to improve catalytic and stability performance, is successfully constructed by the strategy of growth on the surface of ultrathin CeO nanosheets being functionalized with monolayer carboxylic acid groups. The 2D heterostructure possesses a sandwich structure, where monolayer NiFe-MOFs are coordinated to both the top and bottom surface of CeO nanosheets joining carboxylic acid groups. In particular, CeO with robust coordination plays a significant role in the anchoring of carboxylic acid groups and binding strength of heterostructures. The 2D CeO@NiFe-MOF heterostructure with a joint effect of metal-ligand coordination not only presents good structural stability but also significantly enhances the oxygen evolution reaction (OER) efficiencies in comparison to bare NiFe-MOFs, achieving a current density of 20 mA cm at a low overpotential of 248 mV as well as durability for at least 40 h. Meanwhile, the electronics, optics, band gap energy and local strains of CeO decorated with 2D NiFe-MOFs are different to the properties of bare CeO. Our study on the construction of an ultrathin CeO surface-coordinated and confined MOF layer may pave a new way for novel 2D MOF composites/heterostructures or multi-functional 2D CeO materials to be used in energy conversion or other fields.