Mechanistic Study of Monolayer NiP2 (100) toward Solar Hydrogen Production

Understanding the catalytic mechanism at the molecular level is critical to the design and exploration of new materials for solar hydrogen production. Herein, the catalytic activity toward hydrogen evolution reaction (HER) is surveyed for all low‐index surfaces of different nickel phosphides (Ni 3 P, Ni 12 P 5 , Ni 2 P, Ni 5 P 4 , NiP, NiP 2 , and NiP 3 ). It is found that the surface P atoms with only one single PP bond possess excellent HER activity. Accordingly, a monolayer NiP 2 (100) is explored as the cathode material. Comprehensive density functional theory study is used to verify the HER activity of this material, including the effect of vacancy and doping. Defect‐free and Zn‐doped monolayer NiP 2 (100) are found to possess excellent HER activity and thermodynamic stability. This crystal facet also has a high density of active sites (0.126 N Å −2 under an applied over‐potential of 200 mV), which is very close to the Pt (111) surface (0.132 N Å −2 ). The low surface energy and strengthened bonding imply that the monolayer NiP 2 (100) can be stable and easy to synthesize. This finding not only promotes a comprehensive understanding of Ni x P y material toward its catalytic activity for HER, but also suggests a possible new material for the experimentalist in the field.