Synthetic Levers Enabling Independent Control of Phase, Size, and Morphology in Nickel Phosphide Nanoparticles

Abstract

Simultaneous control of phase, size, and morphology in nanoscale nickel phosphides is reported. Phase-pure samples of discrete nanoparticles of Ni12P5 and Ni2P in hollow and solid morphologies can be prepared in a range of sizes (10-32 nm) by tuning key interdependent synthetic levers (P:Ni precursor ratio, temperature, time, oleylamine quantity). Size and morphology are controlled by the P:Ni ratio in the synthesis of the precursor particles, with large, hollow particles formed at low P:Ni and small, solid particles formed at high P:Ni. The P:Ni ratio also impacts the phase at the crystallization temperature (300-350 °C), with metal-rich Ni12P5 generated at low P:Ni and Ni2P at high P:Ni. Moreover, the product phase formed can be decoupled from the initial precursor ratio by the addition of more "P" at the crystallization temperature. This enables formation of hollow particles (favored by low P:Ni) of Ni2P (favored by high P:Ni). Increasing temperature and time also favor formation of Ni2P, by generating more reactive P and providing sufficient time for conversion to the thermodynamic product. Finally, increasing oleylamine concentration allows Ni12P5 to be obtained under high P:Ni precursor ratios that favor solid particle formation. Oleylamine concentration also acts to "tune" the size of the voids in particles formed at low P:Ni ratios, enabling access to Ni12P5 particles with different void sizes. This approach enables an unprecedented level of control over phase and morphology of nickel phosphide nanoparticles, paving the way for systematic investigation of the impact of these parameters on hydrodesulfurization activities of nickel phosphides.

Novel preparation of highly dispersed Ni2P embedded in carbon framework and its improved catalytic performance

“…Compared with other samples, the diffraction peaks of Ni 2 P-528 around 38.4 • , 41.7 • , 46.9 • and 48.9 • corresponding to Ni 12 P 5 phase (PDF 22-1190) and those around 40.7 • , 44.5 • , 47.3 • and 55.0 • ascribed to Ni 2 P (PDF 03-0953) were detected. This observation showed that low phosphidation temperature favored the formation of Ni 12 P 5 phase [44]. Peaks related to Ni 12 P 5 phase disappeared with the increase of the phosphidation temperature, while the diffraction peaks of Ni 2 P became gradually sharp and strong, indicating the aggregation of the Ni 2 P particle and this result is consistent with TEM images.…”

“…Ni 2 P-578, phosphorized at 578 K, had the highest active site and chemisorbing ability for H 2 which exhibited the highest catalytic activity for isobutane dehydrogenation among these catalysts. For Ni 2 P-528 sample, lower phosphidation temperatures favored the formation of Ni 12 P 5 phase [44], resulting a lower activity and selectivity. Although the particle size of Ni 2 P-553 sample was much smaller due to the lower phosphidation temperature, only small amount of Ni could be phosphorized and thus the catalyst possessed a low density of surface active sites, leading to an inferior catalytic performance.…”

Phase Directing Ability of an Ionic Liquid Solvent for the Synthesis of HER-Active Ni2P Nanocrystals

“…26 This diffraction peak is in agreement with Brock's observation of the formation of an amorphous Ni-P phase when higher P:Ni stoichiometric ratios are used. 13 In contrast, when ODE is substituted as the solvent, nucleation was not observed until 200-220 ˚C.…”

“…[9][10][11] The binary Ni-P phase diagram is complex, with a large number of thermodynamically stable stoichiometries (Ni 3 P, Ni 5 P 2 , Ni 12 P 5 , Ni 2 P, Ni 5 P 4 , NiP, NiP 2 , and NiP 3 ), thereby creating a synthetic challenge with respect to accessing phase-pure Ni 2 P. In general, increasing the molar equivalents of phosphide precursor, extending the reaction time, and operating at higher temperatures allow the more phosphorus-rich side of the phase diagram to be accessed for colloidal nanocrystals. [12][13][14] Typical methods used to synthesize high-quality colloidal Ni 2 P nanocrystals use traditional organic solvents (e.g., octadecene (ODE), dioctyl ether), expensive and/or reactive phosphide precursors (tri-n-octylphosphine (TOP), white phosphorus (P 4 ), tris(trimethylsilyl)phosphine (P(TMS) 3 ), and tri-n-butylphosphine), high temperatures, and/or multiple-step reactions. 10,[15][16][17] Triphenylphosphine (PPh 3 ) is a low-cost, less-reactive, and more air-stable phosphide precursor (~15% the cost of TOP in price per mole); 18 however, compared to TOP and P(TMS) 3 , nanocrystals synthesized using PPh 3 are typically large (>45 nm), ill-defined, amorphous, and/or not phase pure.…”

Au/Ni12P5 core/shell nanocrystals from bimetallic heterostructures: in situ synthesis, evolution and supercapacitor properties

“…This evidence indicates that the phosphorization process of Ni in an OAm system requires a relatively higher temperature-270 1C-in this work, which is slightly lower than that reported in other work. 30,31 It also indicates that the heterodimer Au-Ni NPs are relatively stable at 230 1C.…”