Bimetallic Phosphide (Ni,Cu)₂P Nanoparticles by Inward Phosphorus Migration and Outward Copper Migration

Bimetallic phosphide nanoparticles are drawing a great interest as a family of nanomaterials. Controlling their fine features such as surface composition, core crystal structure, and overall composition is a key to further application. Copper and nickel are particularly interesting first-row metals for their abundance and relevance in several branches of catalysis. To synthesize crystalline bimetallic phosphide Ni–Cu–P nanoparticles, core–shell copper–nickel nanoparticles were reacted with white phosphorus (P4). Surprisingly, hollow monocrystalline (Ni,Cu)2P nanoparticles were formed alongside Cu nanoparticles and crystallized in a phase isostructural to Ni2P. Using a combination of local and ensemble analytic techniques, we showed that this unique structure is the result of several competing processes: phosphorus migration, interaction of stabilizing ligands with copper as well as metal phosphide phase crystallization. This study provides important mechanistic insights to rationalize bimetallic phosphide nanoparticles syntheses. Beyond metal phosphides, this well-characterized case study about competing diffusion and crystallization processes is of major relevance for the advancement of materials sciences at the nanoscale.