Stable Active Sites on Ni₁₂P₅ Surfaces for the Hydrogen Evolution Reaction

Abstract

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.

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“…The positions of the aforementioned two peaks are the same, regardless of the loading and size of the Ni 12 P 5 particles, however, with a noticeable broadening and pronounced asymmetry of FTIR peak as the loading amount decreased, based on the FWHM analysis (Supplementary Table 4). This indicates that there is a range of surface sites for linearly bonded carbonyl species on the Ni 12 P 5 particles, likely caused by the two distinct types of Ni site in Ni 12 P 5 and their arrangements in different exposed facet 30,31 . Nevertheless, the intensity of the former peak overwhelms that of the latter, indicating that most carbonyl molecules preferred bonding individually to separated Ni atoms over engaging in multi-coordinate bonding.…”