In the past decade, nickel phosphide (Ni2P) has garnered considerable interest due to the earth abundance of its constituent elements, its stability in alkaline and acidic media, and its comparable catalytic activity to precious metal catalysts for the hydrodeoxygenation of biomass, hydrodesulfurization of petrol, and the hydrogen evolution reaction. However, current methods of synthesizing high-quality colloidal Ni2P nanocrystals typically use flammable organic solvents. Ionic liquids (ILs) are attractive candidates for use as solvents as a result of their nonflammable nature and high thermal and chemical stability. In addition, the low interfacial tension possessed by ILs tends to result in fast nucleation rates in the context of nanocrystal syntheses, which generally produces smaller particles with higher surface-area-to-volume ratios. Herein, we report the high-temperature synthesis of Ni2P nanocrystals using a 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-Tf2N) IL solvent in combination with triphenylphosphine (PPh3) as a low-cost and less-reactive phosphine source, yielding smaller, phase-pure Ni2P nanocrystals in shorter times and lower temperatures compared to the standard reported methods. When the IL solvent was replaced with the prototypical high-boiling organic solvent 1-octadecene under otherwise identical reaction conditions, mixed-phased products containing the undesired nickel-rich Ni12P5 and the target Ni2P were obtained. We will discuss the viability of the resulting Ni2P nanocrystals synthesized in IL for the hydrogen evolution reaction, and extension of the synthesis method to the preparation of Ni2–xCoxP nanocrystals.

Phase directing ability of an ionic liquid solvent for the synthesis of colloidal Ni2P nanocrystals

255th National Meeting (2018)

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