The surface stability and equilibrium crystal morphology of Ni₂P nanoparticles and nanowires from an ab initio atomistic thermodynamic approach

Knowledge of the equilibrium crystal shape and structure of the exposed surfaces of nickel phosphide (Ni₂P) nanostructures is essential for understanding and control of their catalytic performance. Ab initio atomistic thermodynamics was used to investigate computationally the effects of the experimental conditions (temperature, pressure, and chemical potentials) on the relative stabilities of low-Miller index surfaces and on the equilibrium crystal morphology of Ni₂P nanoparticles and nanowires. The P-covered (0001)-Ni₃P₂ (denoted as (0001)-A-P) surface was found to be the most stable surface at a considerably wide range of chemical potentials, whereas the (0001)-A, (101)-Ni/P and (102)-Ni/P surfaces are the thermodynamically most favored phases just in narrow chemical potential regions. The theoretical equilibrium shapes and structures of the Ni₂P nanoparticles and nanowires were obtained based on the Wulff construction at various chemical potentials. The morphology of the surfaces of the Ni₂P nanoparticles and nanowires does depend on the chemical potential; thus, it can be tailored for particular applications by a suitable choice of experimental conditions. The (0001), (100) and (101) side facets dominate the nanoparticle surface in a wide range of chemical potentials but other side facets can also appear at particular ranges of chemical potentials. Results reported herein give new insight into the Ni₂P nanoparticle morphology showing how it depends on the experimental conditions; this information can help to tailor the surface and shape of Ni₂P nanoparticles for specific applications, e.g., in catalysis.