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

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 degrees C. Meanwhile, the addition of TiP, MnP, and Fe2P also reduce the dehydrogenation peak temperature of MgH2 to 343 degrees C, 348 degrees C, and 360 degrees 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.