Stable Phosphorus-Enriched (0001) Surfaces of Nickel Phosphides

Abstract

In heterogeneous catalysis, catalyst synthesis precedes operation and, in most cases, is conducted in an altogether different chemical environment. Thus, determination of the structure and composition of the catalyst surface(s) due to fabrication is essential in accurately evaluating their eventual structure(s) during operation, which provides the origin of their catalytic activities and are therefore key to catalyst optimization. We explore the reconstructions of both Ni2P­(0001) and Ni5P4(0001)/(0001̅) surfaces with first-principles density functional theory (DFT). Most of the stable terminations under realistic synthesis conditions are determined to be P-rich on both materials. A P-covered reconstruction of the Ni3P2 termination of Ni2P­(0001) is found to be most stable, consistent with the current literature. By contrast, the most energetically favorable surfaces of Ni5P4 are found to be the Ni3P3 and Ni4P3 bulk-derived terminations with P-adatoms. The preferred excess P binding sites and their energies are identified on each surface. We find that the P3 site, which is present on Ni5P4, and the Ni3 site, which is present on both Ni2P and Ni5P4, strongly bind excess P. Additionally, we predict the presence of stable P n (n = 2, 4) agglomerates on Ni5P4 at the P3-hollow and Ni–Ni bridge sites. This study highlights the importance of considering the aggregation behavior of nonmetal components in predicting the surface reconstruction of transition metal compounds.

Structure–Activity Relationships for Pt‐Free Metal Phosphide Hydrogen Evolution Electrocatalysts

“…The actual surface is enriched in P due to additional top‐most phosphorus layer. Computational efforts confirmed the experimental findings–the phosphorus‐rich termination of Ni 2 P and Ni 5 P 4 …”

“…Hydrogen absorption on the different crystallographic faces of TMP crystals has been intensively characterized computationally . For example, Jaramillo et al.…”

Flexible Molecular Precursors for Selective Decomposition to Nickel Sulfide or Nickel Phosphide for Water Splitting and Supercapacitance

“…NiP‐1 showed a higher specific capacitance of 1672 F g −1 and NiP‐2 displayed a specific capacitance of 1081 F g −1 at 2 mV s −1 . The supercapacitance of a material is influenced by its electrical conductivity and metal‐rich phosphides (M x P y x > y ) tend to show better electrical conductivity than their metal‐deficient analogues . NiP‐1 (Ni 2 P) has about 66.6 % Ni in its structure compared to NiP‐2 (Ni 5 P 4 ) with 55.55 %.…”

Stable Active Sites on Ni12P5 Surfaces for the Hydrogen Evolution Reaction

“…Figure b shows the surface energies for all stable low‐index surfaces. Compared to other phosphides, bulk Ni 12 P 5 is thermodynamically stable at −1.18 eV < Δ μ p < −0.48 eV . Among the different surface terminations, that is, P‐rich, stoichiometric, and Ni‐rich, all the stable surface energies have a negative slope (Figure b).…”

“…Compared to other phosphides, bulk Ni 12 P 5 is thermodynamically stable at À1.18 eV < Δμ p < À0.48 eV. [20] Among the different surface terminations, that is, P-rich, stoichiometric, and Ni-rich, all the stable surface energies have a negative slope ( Figure 1b). This means that the P-rich surfaces with different terminations are stable, which is in agreement with previous results.…”