Influence of Hydrogen-Incorporation on the Bulk Electronic Structure and Chemical Bonding in Palladium

TL;DR

This study uses in-situ ambient-pressure hard X-ray photoelectron spectroscopy to directly analyze how hydrogen incorporation affects the bulk electronic structure and chemical bonding in palladium, revealing new insights into metal-hydrogen interactions.

Contribution

It presents the first in-situ AP-HAXPES analysis of hydrogen in Pd, linking hydrogen loading to electronic and structural changes under realistic conditions.

Findings

Hydrogen loading causes lattice expansion in Pd.

Electronic structure near the Fermi level is modified by hydrogen.

AP-HAXPES effectively probes bulk properties of metal hydrides.

Abstract

Palladium hydride is a model system for studying metal-hydrogen interactions. Yet, its bulk electronic structure has proven difficult to directly probe, with most studies to date limited to surface-sensitive photoelectron spectroscopy approaches. This work reports the first in-situ ambient-pressure hard X-ray photoelectron spectroscopy (AP-HAXPES) study of hydrogen incorporation in Pd thin films, providing direct access to bulk chemical and electronic information at elevated hydrogen pressures. Structural characterisation by in-situ X-ray diffraction and neutron reflectometry under comparable conditions establishes a direct correlation between hydrogen loading, lattice expansion, and electronic modifications. Comparison with density functional theory (DFT) reveals how hydrogen stoichiometry and site occupancy govern the density of occupied states near the Fermi level. These results resolve long-standing questions regarding PdH and establish AP-HAXPES as a powerful tool for probing the bulk electronic structure of metal hydrides under realistic conditions.