Two-dimensional metal (oxy)hydroxide and oxide ultrathin nanosheets via liquid phase epitaxy

Abstract

Single- or few-layer transition metal (TM) (oxy)hydroxide and oxide nanosheets are promising two-dimensional (2D) nanomaterials for catalysis and energy storage owing to their plentiful active sites. Facile and scalable synthesis of these 2D ultrathin nanosheets, however, is still a great challenge. Here, we report a liquid phase epitaxy (LPE) method to synthesize single- and few-layer TM (oxy)hydroxide and oxide nanosheets (β-Ni(OH)2, δ-FeOOH, β-CoOOH, and monoclinic LixMnO2) with high-yield and rapid procedure. In the LPE synthesis, the preformed Li2O2 nanosheets with (001) exposed planes function as substrates, enabling the epitaxial growth of TM hydroxides with coherent interface. The final TM (oxy)hydroxides and oxides ultrathin nanosheets can be obtained by in situ oxidation and removal of Li2O2 with simple distilled water washing. To demonstrate their potential applications, the obtained single- and few-layer β-Ni(OH)2 ultrathin nanosheets are coupled with functionalized graphene sheets (FGS), and tested as catalysts for oxygen evolution reaction (OER) and as cathodes for alkaline Ni/Fe battery. Importantly, the single-layer β-Ni(OH)2/FGS composite electrode exhibits excellent catalytic performance for OER and superior charge storage capability for Ni/Fe battery. The present work provides new opportunity for the high-yield synthesis of 2D materials for energy-related applications and beyond.