Synthesis of single crystalline two-dimensional transition-metal phosphides via a salt-templating method.

Transition-metal phosphides (TMPs) are considered as promising non-noble electrochemical catalysts for hydrogen evolution reaction (HER). Their highly active sites are located on certain facets, and single crystalline two-dimensional (2D) structures enable them to expose the most active facets for HER. However, the synthesis of single crystalline 2D TMPs is still a challenge owing to their intrinsically non-layered structures. Herein, we demonstrate the synthesis of various single crystalline 2D TMPs (Co2P, MoP2, Ni12P5 and WP2) by a salt-templating method. The as-synthesized 2D Co2P exhibited efficient electrocatalytic ability for HER with an overpotential of 41 mV at 10 mA cm-2 and a Tafel slope of 35 mV dec-1 in 0.5 M H2SO4 solution. We expect that the synthesis of 2D TMPs reported here will open the way to expand the family of 2D materials for electrocatalysis and beyond.