Hydrogen Purification in Palladium-Based Membranes: An Operando X-ray Diffraction Study

Abstract

Palladium (Pd)-based membranes are highly selective to H2, compact, and operationally flexible, and they could facilitate efficient and on-demand production of H2 as a clean energy carrier. For the first time, we designed an operando X-ray diffraction (XRD) experiment to study a dense Pd membrane during H2 permeation at typical operating conditions (e.g., 280–440 °C and 1–3 bar pressure difference). By correlating the lattice structure of a metallic membrane with its gas-separation performance in real time, the operando XRD experiment could serve as a diagnostic tool for research on high-temperature gas-separation membranes. As a proof-of-concept study, we simultaneously collected H2-flux and transmission-XRD measurements, from which we calculated key hydrogen-transport properties, including permeability, solubility, and diffusivity. We also showed that the Pd lattice remained in the α phase throughout the operating conditions investigated. These results are in reasonable agreement with the literature.