W Doping in Ni 12 P 5 as a Platform to Enhance Overall Electrochemical Water Splitting.

Bifunctional electrocatalysts for efficient hydrogen generation from water splitting must overcome both the sluggish water dissociation step of the alkaline hydrogen evolution half-reaction (HER) and the kinetic barrier of the anodic oxygen evolution half-reaction (OER). Nickel phosphides are a promising catalysts family and are known to develop a thin active layer of oxidized Ni in an alkaline medium. Here, Ni 12 P 5 was recognized as a suitable platform for the electrochemical production of γ-NiOOH─a particularly active phase─because of its matching crystallographic structure. The incorporation of tungsten by doping produces additional surface roughness, increases the electrochemical surface area (ESCA), and reduces the energy barrier for electron-coupled water dissociation (the Volmer step for the formation of H ads ). When serving as both the anode and cathode, the 15% W-Ni 12 P 5 catalyst provides an overall water splitting current density of 10 mA cm -2 at a cell voltage of only 1.73 V with good durability, making it a promising bifunctional catalyst for practical water electrolysis.