Synthesis of transition-metal polyphosphides

Abstract

This dissertation describes the synthesis of several transition-metal polyphosphides including orthorhombic FeP 2 , cubic CoP 3 , cubic NiP 2 , monoclinic PdP 2 and monoclinic CuP 2. The investigation of these materials was initiated by the discovery of MP x formation upon reacting a metal halide with molecular yellow P 4 in superheated toluene. When these MP x products were annealed at moderate temperatures (350-500 °C), crystalline phosphorus-rich phases were produced. We found that these phases have been previously synthesized from high-temperature elemental reactions and that low temperature routes to these phase-pure polyphosphides using at least one non-elemental source were not found in the literature. The absence of low-temperature, "bottom up" routes to these materials encouraged us to investigate our initial findings further, as such methods provide unique chemical and structural flexibility in materials synthesis. Metal-rich counterparts to the aforementioned polyphosphides have been successfully produced via molecular solvothermal reactions. These reports consistently used an excess of phosphorus in their reactions but still afforded metal-rich products, and often produced materials with a combination of metal-rich and phosphorus-rich phases. These routes show the inability to dial in the phosphorus content of the produced MP x phases and so they were unable to use balanced stoichiometry to rationalize the chemistry, and rarely attempted to identify reaction byproducts. This prompted us to design a synthesis in which discrete amounts of a phosphorus reagent could be used to target specific compositions and phases and allow for byproduct identification. In order to determine reaction byproducts, a metal halide and yellow P 4 were reacted in together without solvent in sealed ampoules. The clear liquid byproduct was identified as PCl 3 or PBr 3 , indicating that stoichiometric and balanced reactions were possible. In these reactions, metal halides and phosphorus (red or yellow) were balanced such that the chloride was ideally removed has PCl 3 and any remaining phosphorus was used to form targeted, phase-pure MP x phases. Using this stoichiometry in solid-state reactions, all of the aforementioned polyphosphide phases were synthesized as phase pure products at moderate temperatures (500-700 °C). By pelletizing the metal halide reagents in reactions with yellow P 4 or by co-pelletizing the metal halide with red phosphorus, porous pellet products reminiscent of the reagent pellet could be afforded. The reaction stoichiometries used in solid-state reactions were adapted to solvothermal reactions. In these reactions, amorphous MP x products were synthesized from metal halides and yellow P 4 in various solvents (superheated toluene, 1-octadecene and hexadecane), and upon annealing (350-500 °C), targeted phase-pure CoP 3 , NiP 2 and CuP 2 were produced. Reactions substituting red phosphorus for yellow P 4 in hexadecane reactions also yielded the same crystalline phases. Solvothermal reactions were modified by...

Direct Synthesis of CuP2 and Cu3P and Their Performance as Electrocatalysts for Hydrogen Evolution, Oxygen Evolution, and Oxygen Reduction Reactions

“…Although CuP 2 is the more thermodynamically stable phase [17], common wet-chemical synthesis (with phosphine) always generates Cu 3 P [20]. CuP 2 can be synthesized by ball-milling [21,22], solvothermal [23], and solid-gas reaction [24], which usually requires high temperature or vacuum annealing. Barry et al reported that the synthesis of amorphous CuP 2 by mixing copper chloride and white and red phosphorus as a solid pallet can lower the annealing temperature to 500 • C [25].…”