Size-dependent magnetic and electrocatalytic properties of nickel phosphide nanoparticles

Graphical abstract: - Highlights: • Ni₂P nanoparticles (NPs) with different sizes were synthesized via thermal decomposition of single-source precursor. • The size of Ni₂P NPs can easily be controlled by changing reaction temperature. • The smaller Ni₂P NPs exhibit superparamagnetism and the larger Ni₂P NPs exhibit ferromagnetic characteristic at 300 K. • The Ni₂P NPs with small size exhibit higher electrocatalytic activity for the HER. • The magnetic and electrocatalytic properties of the Ni₂P NPs are size-dependent. - Abstract: Nickel phosphide (Ni₂P) nanoparticles (NPs) with different sizes were synthesized via thermal decomposition of bis(triphenylphosphine)nickel dichloride precursor in the presence of oleylamine. The size of the as-synthesized Ni₂P NPs could easily be controlled by increasing the reaction temperature from 300 to 340 °C. The structure and morphology were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption–desorption and X-ray photoelectron spectroscopy (XPS). Then the influences of the size of the Ni₂P NPs on the magnetic and electrocatalytic properties were investigated systematically. The results indicate that the as-synthesized Ni₂P NPs exhibit ferromagnetic characteristic at 5 K. The Ni₂P NPs with small size exhibit superparamagnetism and the larger size exhibit ferromagnetic characteristic at 300 K. The blocking temperature, saturation magnetization, remanent magnetization and coercivity increased significantly with the increase of size of Ni₂P NPs, indicating the strong size effect of Ni₂P NPs for magnetic properties. Electrochemical tests indicate that the catalytic activity can be enhanced by decreasing the size of Ni₂P NPs. Due to the larger electrochemical active surface area and higher electrical conductivity, the Ni₂P NPs with small size exhibit higher electrocatalytic activity. This work suggests that the size of Ni₂P NPs is an important factor to affect the magnetic and electrocatalytic properties.