Nonequilibrium Low-Temperature Synthesis of Platinum Hydride and In Situ Structural Characterization Using Temperature-Dependent Ion Beam Analyses.

Hydrogen readily migrates through various materials because of its small atomic size and light mass. Despite emerging functionalities, however, introducing hydrogen atoms into metals that are intrinsically unfavorable to hydrogen remains challenging and has generally required high-pressure conditions. To overcome this limitation, we adopted a nonequilibrium and low-temperature approach using hydrogen ion implantation below ∼50 K, through which we successfully synthesized platinum hydride (PtHx) with a maximum hydrogen concentration of x ∼ 0.2. The resulting structure was characterized in situ through temperature-dependent ion beam analyses using nuclear reaction analysis (NRA) and Rutherford backscattering spectrometry (RBS), combined with ion channeling. We found that H atoms are likely to occupy the tetrahedral interstitial sites, and that the Pt lattice, perturbed by the incorporated H atoms, recovers upon dehydrogenation. These findings demonstrate that nonequilibrium low-temperature synthesis enables reversible hydrogenation in materials traditionally considered unfavorable to hydrogen incorporation, opening new pathways for exploring switchable metastable hydride phases.