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.%), MgH 2 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 MgH 2 ’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 MgH 2 to fabricate a composite hydrogen storage system, thereby boosting the overall hydrogen storage properties of MgH 2 . Results indicate that the Ce-doped alloy eliminates the initial long hydrogen absorption induction period and exhibits rapid hydrogen absorption capability. The optimal MgH 2 /10 wt.% HEA composite for hydrogen storage incorporates a Ce-doped alloy and MgH 2 . MgH 2 /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 MgH 2 -alloy, the Ce element in the alloy will interact with MgH 2 to partially absorb hydrogen to form CeH 2.51 in situ and generate a hydride FCC-MH phase. During hydrogen absorption/desorption, CeH 2.51 and the alloy serve as nucleation sites for MgH 2 , effectively promoting its hydrogenation/dehydrogenation reactions and exerting a “hydrogen overflow” effect. Additionally, the alloy’s self hydrogen absorption/desorption drives MgH 2 ’s hydrogenation/dehydrogenation, functioning as a “hydrogen pump”. The hydrogen absorption/desorption properties of MgH 2 were notably optimized via the synergistic catalysis of CeH 2.51 and the alloy. This work offers novel insights for designing and catalytically modifying new MgH 2 catalysts.