Water-Induced Formation of Ni2 P-Ni12 P5 Interfaces with Superior Electrocatalytic Activity toward Hydrogen Evolution Reaction.

The interface between two material phases typically exhibits unique electronic states distinct from their pure phases, thus, providing a very promising channel to construct catalysts with excellent activity and stability. Here, water-induced formation of Ni2 P-Ni12 P5 through a one-step phosphorization of nickel foam (NF) is demonstrated for the first time. The abundant interfaces endow Ni2 P-Ni12 P5 /NF with excellent electrocatalytic hydrogen evolution reaction (HER) activity in alkaline condition, with an overpotential of 76 mV at a current density of 10 mA cm-2 and of 147 mV at a current density of 100 mA cm-2 , and a Tafel slope of 68.0 mV dec-1 . The Ni2 P-Ni12 P5 /NF also exhibits better durability than Pt/C/NF during HER at relatively large overpotential. Density functional theory calculations show that the electronic states at the Ni2 P-Ni12 P5 interface are greatly altered, which enables optimal hydrogen adsorption, accelerates the charge transfer kinetics, and thus enhances the HER electrocatalytic activity. Superior overall water-splitting performance is also obtained by combining Ni2 P-Ni12 P5 /NF with NiFe-layered double hydroxide (LDH) oxygen evolution reaction (OER) catalyst. Overpotentials of the cell for achieving 10 mA cm-2 are only 324 mV. This work provides a facile method for the preparation of interfaces between different nickel phosphide polymorphs toward HER.