Medium-entropy oxyfluoride-derived catalytic nanoparticles for enhancement of dehydrogenation kinetics of magnesium hydride

Magnesium hydride has a hydrogen capacity of 7.6 wt%, thereby being believed as a potential candidate for solid-state hydrogen storage. Nevertheless, the slow dehydrogenation kinetics severely hampers its practical utilizations. Herein, a medium-entropy oxyfluoride (Ti_0.25V_0.25Nb_0.25Zr_0.25)O_1.5F_1.5 (MEOF) is synthesized as an additive to accelerate hydrogen release from MgH₂. After introducing the as-prepared oxyfluoride (10 wt%) into MgH₂, the superior dehydrogenation kinetics with an activation energy of 67.7 kJ mol⁻¹ is achieved. Even after fifty de/hydrogenation cycles, the dehydrogenation activation energy and capacity retention still remain at 70.7 kJ mol⁻¹ and 98.5 %, respectively; showing excellent cycle durability. Further investigation demonstrates that the significant kinetic enhancement is attributed to the synergistic catalysis of extremely dispersed transition metal phases which are in-situ formed in the preparation process of MEOF-doped MgH₂ composite. Meanwhile, the improvement of cycling durability is owed to the inhibitory effect of in-situ generated MgF₂ and MgO on crystallite growth and powder agglomeration. These results bring insight into the importance of multiphase synergy in improving hydrogen desorption performance of magnesium hydride.