Control of Branching in Ni₃C_1–xNanoparticles and Their Conversion into Ni₁₂P₅Nanoparticles

Dendritic Ni 3 C 1– x nanoparticles (NPs) with controlled branching have been synthesized through the thermolysis (230 °C) of nickel acetylacetonate using oleylamine as a reducing agent and 1-octadecene (ODE) as the solvent. Addition of trioctylphosphine (TOP) as a ligand inhibits formation of dendritic shapes and prevents incorporation of C, resulting in spherical Ni NPs. In comparison, when using octadecane (ODA) or trioctylphosphine oxide (TOPO) as the solvent, Ni NPs are obtained at 230 °C that have fewer, larger branches than when using ODE. Higher temperatures are required for incorporation of C from ODA or TOPO into Ni NPs, resulting in Ni 3 C 1– x NPs. Therefore, the allyl group in ODE facilitates formation of Ni 3 C 1– x NPs at lower temperatures. Conversion of dendritic Ni 3 C 1– x NPs into Ni 12 P 5 NPs after adding TOP and heating to 300 °C results in the formation of multiple voids in the branches, rather than yolk-in-shell structures or unfilled single voids observed for spherical NPs.