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New progress in atomic imaging of hydrogen in metal hydrides
Recently, Associate Professors Lin Gan and Jia Li from Tsinghua Shenzhen International Graduate School (Tsinghua SIGS) and Associate Professor Lin Xie from Southern University of Science and Technology (SUSTech) have made significant progress in revealing the occupation structure of subsurface hydrogen interstices in palladium hydrides. The work was published in the renowned international journal Angewandte Chemie International Edition titled "Atomic Imaging of Subsurface Interstitial Hydrogen and Insights into Surface Reactivity of Palladium Hydrides” .
Palladium (Pd) is a metal with the ability to absorb large quantities of hydrogen. Pd hydrides hold important applications in hydrogen sensor, storage, purification, and more recently in electrocatalysis. To understand the hydrogen storage mechanism of Pd and the electrocatalytic properties of Pd hydrides, it is crucial to reveal the atomic occupation of hydrogen in Pd. However, since hydrogen is the lightest element and scatters X-ray and electrons rather weakly, it is extremely difficult to detect the interstitial hydrogen atoms in metal hydrides using traditional X-ray diffraction and transmission electron microscopes.
In the recent collaborative work, SIGS and SUSTech researchers achieved the first direct imaging of subsurface hydrogen atoms absorbed in Pd nanoparticles by using differentiated and integrated differential phase contrast within an aberration-corrected scanning transmission electron microscope, a new technique that allows improved imaging contrast for light elements. In contrast to the well-established octahedral interstitial sites for hydrogen in the bulk Pd, subsurface hydrogen atoms are directly identified to occupy the tetrahedral interstices.
Fig 1. Subsurface Interstitial hydrogen atoms in Pd hydride nanoparticles are directly imaged for the first time by using differentiated and integrated differential phase contrast within aberration-corrected scanning transmission electron microscope.
Using Density Functional Theory calculations, the team further showed that the occupation energy of tetrahedral and octahedral hydrogen interstices at the Pd subsurface are very close, especially when octahedral hydrogen interstices exist in the bulk. It was also found that the amount and the occupation type of hydrogen interstices at the near surface can sensitively control the surface chemical activity of Pd hydrides.
These results are highly important for understanding the hydrogen storage mechanism in Pd as well as surface catalytic activities of Pd hydrides. They also provide insight for designing new Pd-based catalysts based on subsurface hydrogen engineering.
Link to the article: https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202006562
Writer: Kang Yongqiang, Wan Fangxing