Chalcogen-Based Precursors for Transition Metal (Co, Ni) Phosphides: (Di)chalcogenide-to-Phosphide Transformation via Chemical Extraction of Chalcogenides

Abstract

The chemical properties of polymorphic compounds are highly dependent on their stoichiometry and atomic arrangements, making certain phases technologically more important. Selective development of these phases is challenging. This study introduces a method where chalcogenide atoms from metal chalcogenides are chemically extracted by trioctylphosphine (TOP) and substituted with phosphide. Using this approach, dithiocarbamate/xanthate complexes of cobalt and nickel were employed for the selective synthesis of pure metal sulfides or phosphides. Optimization yielded either sulfur-deficient phases (Ni₃S₂, Co₉S₈) or a complete transformation to phosphides (Ni₂P, CoP). Likewise, for the first time, selenobenzoate complexes of Ni and Co were used for the synthesis of transition metal diselenides (NiSe₂, CoSe₂), which could then be converted to metal phosphides (Ni₂P, Co₂P). The synthesis used solution-phase thermal decomposition with various precursors, surfactants, and temperatures. With TOP, different phases of metal chalcogenides, metal phosphides, and mixed metal phosphide nanomaterials (NiS, Ni₃S₂, Co₉S₈, NiSe₂, CoSe₂, Ni₂P, Ni₅P₄, Co₂P, CoP, and Ni_2-xCo_<i>x</i>P) were obtained by varying reaction conditions. The formation mechanism of nickel and cobalt phosphide nanoparticles from precursors is proposed, demonstrating that presynthesized metal chalcogenides can be transformed into phosphides, opening a new research avenue for dimensionally controlled metal chalcogenides as templates for metal phosphides.