Mechanical mixtures of metal oxides and phosphorus pentoxide as novel precursors for the synthesis of transition-metal phosphides

Abstract

This study presents a new type of precursor, mechanical mixtures of metal oxides (MOs) and phosphorus pentoxide (P₂O₅) are used to synthesize Ni₂P, Co₂P and MoP phosphides by the H₂ reduction method. In addition, this is first report of common solid-state P₂O₅ being used as a P source for the synthesis of metal phosphides. The traditional precursors are usually prepared via a complicated preparation procedure involving dissolution, drying and calcination steps. However, these novel MOs/P₂O₅ precursors can be obtained only by simple mechanical mixing of the starting materials. Furthermore, unlike the direct transformation from amorphous phases to phosphides, various specific intermediates were involved in the transformation from MOs/P₂O₅ to phosphides. It is worthy to note that the dispersions of Ni₂P, Co₂P and MoP obtained from MOs/P₂O₅ precursors were superior to those of the corresponding phosphides prepared from the abovementioned traditional precursors. It is suggested that the morphology of the as-prepared metal phosphides might be inherited from the corresponding MOs. Based on the results of XRD, XPS, SEM and TEM, the formation pathway of phosphides can be defined as MOs/P₂O₅ precursors → complex intermediates (metals, metal phosphates and metal oxide-phosphates) → metal phosphides.