Effect of Water Vapor on Hydrogen Permeation Behavior Through Tubular Pd-Ag Alloy Membrane and Permeability Recovery

The effect of water vapor (0.1 to 3.0 vol %) on hydrogen permeation through a tubular palladium-silver membrane was investigated at 673 K with a hydrogen concentration of 1%, assuming a purification process for fuel tritium produced in fusion reactor blankets. While permeation under dry conditions exhibited a linear dependence on the hydrogen partial pressure, the introduction of water vapor revealed two distinct inhibition behaviors. At higher water vapor concentrations, a reversible decline in the permeation flux governed by Langmuir-type competitive adsorption occurred. In contrast, the dilute condition of 0.1% led to a continuous and irreversible decline, which was confirmed even in long-term testing over a period of 2 months. A post-experiment surface analysis revealed an increase in the oxygen content on the membrane surface near the outlet. Furthermore, it was demonstrated that this degraded permeability could be significantly recovered by reduction treatment in a high-concentration hydrogen atmosphere.