Stable Active Sites on Ni12P5 Surfaces for the Hydrogen Evolution Reaction

Knowledge of the active sites and stability of the materials is imperative for improving the properties of electrocatalysts for water splitting. The aim of the current work is to understand the active sites and stability of Ni12P5 for hydrogen evolution reaction (HER). Activity and stability of the reaction sites on different low-index surfaces of Ni12P5, namely (001), (100), (110), (101), and (111) planes with different terminations, are studied using density functional theory calculations. The results show that the top P sites with a coordination number of 5 or 7 and some coplanar-bridged NiNi sites are favorable for HER, whereas hollow NiNiNi sites are not suitable. Among these active sites, the active Ni sites with higher coordination number are stable, whereas the active Ni atom with lower coordination number is unstable. This study supports the idea that catalytically active and chemically stable sites are not mutually exclusive. This finding has broadened the understanding of the root causes of electrocatalytic activity and stability of phosphides. Ideally, the (101) surface of Ni12P5 with P-rich termination should be prepared in the experiment for stable and active HERs.