We investigated the atomic structure of graphene supported Pd nanoclusters and their interaction with hydrogen up to atmospheric pressures at room temperature by surface X-ray diffraction and scanning tunneling microscopy. We find that Ir seeded Pd nanocluster superlattices with 1.2 nm cluster diameters can be grown on the graphene/Ir(111) moiré template with high structural perfection. The superlattice clusters are anchored through the rehybridized graphene to the Ir support, which superimposes a 2.0% inplane compression onto the clusters. During hydrogen exposure at 10 mbar pressure and room temperature, a significant part of the clusters gets unpinned from the superlattice. The clusters in registry undergo an out-of-plane expansion only, whereas the detached clusters expand in in- and out-of-plane directions. The formation of a hydrogen rich PdH_x α′ phase was not observed. After exposure to 1 bar, the majority of the clusters are unpinned from superlattice sites, due to their surface interaction with hydrogen and possible spill over to the graphene support. Only minor sintering was observed, which is more pronounced for the unpinned clusters. The results give evidence that ultrasmall Pd clusters on graphene are a stable hydrogen storage system with reduced hydrogen storage hysteresis and maintain a large surface area for hydrogen chemisorption.

中文翻译：

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石墨烯负载钯纳米团簇的氢溶解度和原子结构

我们通过表面 X 射线衍射和扫描隧道显微镜研究了石墨烯支持的 Pd 纳米团簇的原子结构及其在室温下与氢气的相互作用。我们发现具有 1.2 nm 簇直径的 Ir 种子 Pd 纳米簇超晶格可以在石墨烯 / Ir（111）莫尔模板上生长，具有高度的结构完美性。超晶格簇通过再杂化的石墨烯锚定到 Ir 载体上，从而在簇上叠加 2.0% 的面内压缩。在 10 毫巴压力和室温下暴露于氢气期间，大部分团簇从超晶格中脱离。注册中的集群仅进行平面外扩展，而分离的集群在平面内和平面外方向上扩展。富氢PdH的形成未观察到_x α' 相。暴露于 1 bar 后，由于它们与氢的表面相互作用以及可能溢出到石墨烯载体上，大多数簇从超晶格位点脱离。仅观察到轻微的烧结，这对于未钉扎的簇更为明显。结果表明，石墨烯上的超小 Pd 簇是一种稳定的储氢系统，具有减少的储氢滞后并保持较大的表面积以进行氢化学吸附。