Study on the hydrogen storage performance mechanism of MgH2 co-modified by rare earth hydride and high entropy hydrogen storage alloy based on in-situ differentiation

Owing to its high hydrogen storage capacity (7.6 wt%), MgH2 is regarded as a highly promising solid-state hydrogen storage material. Nonetheless, its commercialization is constrained by high thermodynamic stability and sluggish hydrogen sorption kinetics. Thus, catalyst introduction is essential to enhance MgH2’s hydrogen storage performance. This study designed and synthesized a hydrogen storage high-entropy alloy, TiVCrZrNbCe. Upon doping with Ce to enhance activation, the alloy was combined with MgH2 to fabricate a composite hydrogen storage system, thereby boosting the overall hydrogen storage properties of MgH2. Results indicate that the Ce-doped alloy eliminates the initial long hydrogen absorption induction period and exhibits rapid hydrogen absorption capability. The optimal MgH2/10 wt% HEA composite for hydrogen storage incorporates a Ce-doped alloy and MgH2. MgH2/10 wt% HEA shows initial/peak dehydrogenation temperatures of 205/270 °C, releases 6.05 wt% hydrogen, and enables rapid hydrogen absorption at room temperature. The hydrogen sorption activation energies are reduced to 40.8/76.8 kJ mol−1, and the capacity maintains well over ten cycles. Microstructure and mechanism analyses reveal that during ball milling of the MgH2-alloy, the Ce element in the alloy will interact with MgH2 to partially absorb hydrogen to form CeH2.51 in situ and generate a hydride FCC-MH phase. During hydrogen absorption/desorption, CeH2.51 and the alloy serve as nucleation sites for MgH2, effectively promoting its hydrogenation/dehydrogenation reactions and exerting a “hydrogen overflow” effect. Additionally, the alloy’s self hydrogen absorption/desorption drives MgH2’s hydrogenation/dehydrogenation, functioning as a “hydrogen pump”. The hydrogen absorption/desorption properties of MgH2 were notably optimized via the synergistic catalysis of CeH2.51 and the alloy. This work offers novel insights for designing and catalytically modifying new MgH2 catalysts.