Permeation hysteresis in PdCu membranes

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Palladium-copper (PdCu) alloys are crucial for hydrogen separation membranes.
• Understanding phase transitions in PdCu under hydrogen is vital for membrane performance.
• Hysteresis in hydrogen permeation affects the stability and efficiency of PdCu membranes.

Purpose of the Study:

• To investigate hydrogen permeation hysteresis in PdCu membranes.
• To analyze the structural changes and phase transitions during hydrogen cycling.
• To determine the kinetics of hydrogen diffusion in different phases of PdCu.

Main Methods:

• Fabrication of a 3 µm thick supported PdCu membrane.
• Hydrogen permeation experiments across the fcc/bcc miscibility gap (723-873 K).
• Structural analysis of membrane fragments using X-ray diffraction (XRD) after annealing under H2.

Main Results:

• Observed significant hydrogen permeation hysteresis during cycling through the fcc/bcc miscibility gap.
• Identified retardation of the face-centered cubic (fcc) to body-centered cubic (bcc) transition.
• Attributed this retardation to the formation of metastable hydrogenated fcc PdCu(H) phases.
• Quantified hydrogen flux in the bcc phase (below 723 K) and fcc phase (above 873 K) with distinct activation energies.

Conclusions:

• Metastable hydrogenated fcc PdCu(H) phases play a critical role in hydrogen permeation hysteresis.
• The observed hysteresis impacts the operational stability of PdCu membranes.
• Kinetic data provides insights into hydrogen diffusion mechanisms in different PdCu phases.