Ultrathin two-dimensional layered metal hydroxides: an emerging platform for advanced catalysis, energy conversion and storage

The unique properties of graphene are triggering a great deal of attention toward the family of ultrathin two-dimensional (2D) structures. Ultrathin layered metal hydroxides (LMHs) are increasingly being recognized as an important category in 2D nanomaterials, and the corresponding research has been experiencing a significant renaissance. Due to the flexible tunability of metal ions, their naturally positively charged plane and 2D anisotropy with nanometre thickness, ultrathin LMHs and their derived hybrids have shown exciting perspectives in many fields, such as catalysis, and energy storage and conversion. As for practical application, ultrathin 2D LMHs have exhibited high performances in electrocatalysis (e.g. the hydrogen and oxygen evolution reactions), photocatalysis and supercapacitors. In particular, hybrid materials based on ultrathin LMHs have proven to further improve the catalytic performance by synergistic effects derived from the hybrid interfaces. Nevertheless, studies on ultrathin LMHs are still in the infant stage and lag far behind other important 2D nanomaterials. Hence, it is essential to update the reported work in this emerging research area. In this tutorial review, we aim to summarize recent developments in ultrathin LMHs and their derived hybrids. The quite dispersed literature regarding ultrathin LMH-based materials is classified under the framework of catalysis-and energy-related properties and applications.