PdNi Biatomic Clusters from Metallene Unlock Record‐Low Onset Dehydrogenation Temperature for Bulk‐MgH₂

Abstract Hydrogen storage has long been a priority on the renewable energy research agenda. Due to its high volumetric and gravimetric hydrogen density, MgH₂ is a desirable candidate for solid‐state hydrogen storage. However, its practical use is constrained by high thermal stability and sluggish kinetics. Here, PdNi bilayer metallenes are reported as catalysts for hydrogen storage of bulk‐MgH₂ near ambient temperature. Unprecedented 422 K beginning dehydrogenation temperature and up to 6.36 wt.% reliable hydrogen storage capacity are achieved. Fast hydrogen desorption is also provided by the system (5.49 wt.% in 1 h, 523 K). The in situ generated PdNi alloy clusters with suitable d‐band centers are identified as the main active sites during the de/re‐hydrogenation process by aberration‐corrected transmission electron microscopy and theoretical simulations, while other active species including Pd/Ni pure phase clusters and Pd/Ni single atoms obtained via metallene ball milling, also enhance the reaction. These findings present fundamental insights into active species identification and rational design of highly efficient hydrogen storage materials.