Introducing transition metal phosphides as catalysts to enhance the hydrogen storage properties of MgH2

Abstract

In this study, some transition metal phosphides (TMPs) were used as catalysts to enhance the hydrogen storage properties of the MgH₂. The MgH₂–5 wt% TMPs composites were prepared by mechanical ball milling. Then the microstructures, phase compositions and hydrogen storage properties of the composites were studied in detail. The results confirm that Co₂P, TiP, MnP and Fe₂P can improve the hydrogen absorption and desorption kinetics of MgH₂. By comparison, Cu₃P and MoP exhibit almost no catalytic effect on hydrogen absorption and desorption reactions of MgH₂, and the dehydrogenation peak temperatures of MgH₂–Cu₃P and MgH₂–MoP are basically the same as that of pure MgH₂. Among these phosphides, Co₂P has the optimal catalytic properties. The dehydrogenation peak temperature of the MgH₂–Co₂P composite is 313 °C. Meanwhile, the addition of TiP, MnP, and Fe₂P also reduce the dehydrogenation peak temperature of MgH₂ to 343 °C, 348 °C, and 360 °C. The formation of Mg₃P₂ and Mg₂CoH₅ phases during the reaction is responsible for the hydrogen absorption and desorption kinetics of MgH₂–Co₂P. The catalytic property of TiP is ascribed to multiple valence Ti sites. While the beneficial catalytic effects of the MnP and Fe₂P can be ascribed to the in-situ formation of Mg₃P₂, Mn and Fe.