Hydrogen sorption by Pd77Ag23 metallic membranes. Role of hydrogen content, temperature and sample microstructure

Permeation across metallic membranes is a process used in the industry for purifying hydrogen. In conventional technology, a few tens of micrometers thick metallic membranes made of palladium alloys are used in the 400–600 °C temperature range, using a driving force of several bars for enhanced kinetics. In stationary conditions of flow, the diffusion-controlled transport of atomic hydrogen across the membrane is usually rate-determining. When thin (sub-micron thick) membranes are used, surface rate contributions become more significant. To optimize permeation performances, there is therefore a need for separately measuring surface and bulk rate contributions. In this communication, we report on the kinetics of hydrogen permeation across Pd77Ag23 metallic membranes using pneumato-chemical impedance spectroscopy. The role of different operating parameters (temperature, surface state, membrane microstructure) on the kinetics of permeation is analyzed and discussed.