Crystal and Electronic Facet Analysis of Ultrafine Ni2P Particles by Solid-State NMR Nanocrystallography

Abstract

Structural and morphological control of crystalline nanoparticles is crucial in the field of heterogeneous catalysis and the development of “reaction specific” catalysts. To achieve this, colloidal chemistry methods are combined with ab initio calculations in order to define the reaction parameters, which drive chemical reactions to the desired crystal nucleation and growth path. Key in this procedure is the experimental verification of the predicted crystal facet and its corresponding electronic structure, which in case of nanostructured materials becomes extremely difficult. Here, by employing <sup>31</sup>P solid-state nuclear magnetic resonance (ssNMR) aided by advanced density functional theory (DFT) calculations to obtain and assign the Knight shifts, we succeeded in determining the crystal and electronic structure of the terminating surfaces of ultrafine Ni<sub>2</sub>P nanoparticles at atomic scale resolution. Our work highlights the potential of ssNMR nanocrystallography as a unique tool in the emerging field of facet-engineered nanocatalysts.

The Role of Hydrogen Adsorption Site Diversity in Catalysis on Transition Metal Phosphide Surfaces

“…37 Even on the same facet (i.e., Ni2P(0001)), there are multiple possible surface terminations (e.g., Ni3P2 and Ni3P terminations). 37,38 In Figure 2 we summarize the computed HBE on Ni2P(0001) and CoP (101) surfaces from reported values in the literature. The calculated HBE at the Ni3 hollow site on the Ni2P(0001) surface ranges from 0.137 to -0.543 eV.…”

“…Papawassiliou et al found that (0001) surfaces dominate on Ni2P ultrasmall nanoparticles (4 nm diameter), but (101̅ 0) surfaces dominate with larger nanoparticles (12 nm diameter). 37 Even on the same facet (i.e., Ni2P(0001)), there are multiple possible surface terminations (e.g., Ni3P2 and Ni3P terminations). 37,38 In Figure 2 we summarize the computed HBE on Ni2P(0001) and CoP (101) surfaces from reported values in the literature.…”

The Role of Hydrogen Adsorption Site Diversity in Catalysis on Transition Metal Phosphide Surfaces

“…Papawassiliou et al found that (0001) surfaces dominate on Ni2P ultrasmall nanoparticles (4 nm diameter), but (101̅ 0) surfaces dominate with larger nanoparticles (12 nm diameter). 40 Even on the same facet (i.e., Ni2P(0001)), there are multiple possible surface terminations (e.g., Ni3P2 and Ni3P terminations). 40,41 In Figure 2 we summarize the computed HBE on Ni2P(0001) 14,31,34,35,[41][42][43][44] and CoP(101) 14,[45][46][47] surfaces from reported values in the literature.…”

“…40 Even on the same facet (i.e., Ni2P(0001)), there are multiple possible surface terminations (e.g., Ni3P2 and Ni3P terminations). 40,41 In Figure 2 we summarize the computed HBE on Ni2P(0001) 14,31,34,35,[41][42][43][44] and CoP(101) 14,[45][46][47] surfaces from reported values in the literature. The calculated HBE at the Ni3 hollow site on the Ni2P(0001) surface ranges from 0.137 to -0.543 eV.…”

Nickel Phosphide Nanoparticles for Selective Hydrogenation of SO2 to H2S

“…There has been a considerable amount of research focused on Ni 2 P, − and the fine control of its phase and morphology has been discussed through the modification of synthesis parameters. , Other phosphorus-rich phases, such as Ni 5 P 4 , were considered as the active catalyst for the electrocatalytic hydrogen evolution reaction (HER). − However, there was limited research focus on the Ni 5 P 4 phase for the HDS reaction. Compared with Ni 2 P (Ni–Ni bond distance is 3.2 Å on the Ni 3 P­(0001) surface and 2.7 Å on the Ni 3 P 2 (0001) surface), Ni 5 P 4 (Ni–Ni bond distance is 2.4/2.6 Å on the Ni 4 P 3 (0001) surface) , has a closer Ni–Ni distance, and the (0001) surface of Ni 5 P 4 provides the P3-hollow site, which offers nearly optimal hydrogen binding and shows much higher activity for the HER. − Hence, it is anticipated that the Ni 5 P 4 phase would be a potential active phase for HDS, which may provide better performance than Ni 2 P.…”