Atomic Imaging of Subsurface Interstitial Hydrogen and Insights into Surface Reactivity of Palladium Hydrides

Abstract

Resolving interstitial hydrogen atoms at the surfaces and interfaces is crucial for understanding the mechanical and physicochemical properties of metal hydrides. Although palladium (Pd) hydrides hold important applications in hydrogen storage and electrocatalysis, the atomic position of interstitial hydrogen at Pd hydride near surfaces still remains undetermined. We report 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. In contrast to the well-established octahedral interstitial sites for hydrogen in the bulk, subsurface hydrogen atoms are directly identified to occupy the tetrahedral interstices. DFT calculations show that the amount and the occupation type of subsurface hydrogen atoms play an indispensable role in finetuning the electronic structure and associated chemical reactivity of the Pd surface.

Size-dependent hydrogen trapping in palladium nanoparticles

“…As a first step, we determined the most favorable interstitial site occupied by a hydrogen atom in a "bulk" fcc Pd containing 108 atoms. As seen in previous works 54,55 , among the two possible interstitial sites, the octahedral one is the most stable in the bulk, even if the energy difference between both interstitial sites is weak (around 0.1 eV). This stable configuration is not surprising since the octahedral site is larger than the tetrahedral one.…”

Interstitial and substitutional light elements in transition metals for heterogeneous catalysis

“…Along with other supporting techniques and simulations, certain atomic columns observed by microscopy were interpreted as interstitial boron atoms. In 2020, Gan et al 47 reported that the use of a differentiated and integrated differential phase contrast technique (dDPC and iDPC) in aberration-corrected STEM can even directly visualise atomic columns of hydrogen that correspond to interstitial tetrahedral sites in the Pd-H system, which was also supported by simulated dDPC images. On the basis of the result, they claimed that hydrogen can also occupy tetrahedral interstitial sites, which is in agreement with previous NPD studies 48 and theoretical calculations 49 .…”

Emerging interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic elements for electrocatalytic applications

“…11,12,19,20 Usually, those nonmetallic atoms with small atomic radii can easily permeate and occupy the interstitial sites including octahedral (O-site) and/or tetrahedral (T-site) sites of the Pd host lattice. [21][22][23] Moreover, the incorporation of these nonmetallic atoms can expand the lattice spacing of Pd. 11,12,24 Theoretically, the incorporation of nonmetallic atoms into interstitial sites within metal lattices can lead to materials with increased hardness and chemical stability considering the fact the interstitial atoms can strengthen the metal-metal bonding.…”

“…Some organic molecules, including N,N-dimethylformamide (DMF), n-butylamine, formaldehyde or acetaldehyde, can be catalyzed by Pd materials to produce H 2 , which is then dissociated on the Pd surface to generate H adatoms that can permeate into the Pd lattice and finally occupy the interstitial sites to form PdH x . 21,34,[52][53][54] Based on this, PdH x nanomaterials can be obtained by heating Pd nanomaterials or Pd(II) in the above organic solvent, which acts as both a H source and a solvent. Importantly, the formation of trace oxide during this process can passivate the original PdH x surface, thus endowing PdH x with excellent stability.…”