Single‑Atom‑Induced Electronic Polarization at Adjacent Cluster Promotes Efficient Hydrogen Storage in Magnesium Hydride.

Single-atom/cluster composite catalysts demonstrate remarkable advantages in heterogeneous catalysis due to their unique electronic synergy, yet their catalytic performance and mechanisms in solid-state hydrogen storage reactions remain poorly explored. Here we construct a niobium-based single-atom/cluster composite catalyst (NbSA/AC) on magnesium hydride (MgH2), a representative hydrogen-storage material. NbSA/AC enables MgH2 to release approximately 4 wt.% H2 at a temperature as low as 175°C, outperforming both Nb single-atom and cluster catalysts, as well as most reported catalysts. Theoretical calculations reveal a synergistic mechanism of "single-atom-induced interfacial electron polarization of adjacent clusters," clarifying that the clusters act as the main active sites, while the single atoms serve as electronic regulators. During dehydrogenation, Nb single atoms induce a strong electron-deficiency at Nb cluster, weakening the Mg─H bond and promoting hydrogen migration from MgH2 to Nb clusters. During hydrogenation, the single atoms moderately increase the electron density of the clusters, shifting electrons toward higher energy states near the Fermi level, which potentially destabilizes Nb-H interactions and accelerates hydrogen diffusion into the Mg matrix. This work elucidates, for the first time at the atomic scale, the cooperative catalytic mechanism of single-atom/cluster composites on MgH2, providing guidance for the design of efficient hydrogen-spillover catalysts.