In Situ Time-Resolved X-ray Absorption Fine Structure and Small Angle X-ray Scattering Revealed an Unexpected Phase Structure Transformation during the Growth of Nickel Phosphide Nanoparticles

Nickel phosphide (Ni–P) nanoparticles have been extensively studied because of their promising catalytic activities in both hydrogen evolution reaction and oxygen evolution reaction. However, controllable synthesis of the nickel phosphide catalyst is still a challenge because of its complex phase transformations during the synthesis procedure. Deep understanding of the nanoparticle formation mechanism should be taken into account for an efficient catalyst tailoring of size, shape, structure, and eventually performance. Unfortunately, there are only few reports regarding their formation processes. In this regard, we investigated the formation process of Ni–P nanoparticles by a conjunction of in situ X-ray absorption fine structure (XAFS) from the Ni K-edge, ex situ XAFS from the P K-edge, in situ small angle X-ray scattering, and high-resolution transmission electron microscopy techniques. A novel phase structure transformation was unraveled from views of evolutions of chemical valence, coordination struct...