A basic study of high-temperature hydrogen permeation through bcc Pd–Cu alloy foil

•H2 permeability of bcc Pd–Cu alloy foil depends on the Pd content of 54–60 wt.%.•A 54 wt.% Pd–Cu foil showed a quick transition between bcc and fcc at 600–625 °C.•The phase transition of 56 wt.% Pd–Cu is slow in the miscible region at 600 °C.•H2 solubility of the bcc alloy greatly affects the H2 permeability.•Presence of hydrogen stabilizes the bcc structure of Pd–Cu alloy.

The H2 permeability of the Pd–Cu alloy foil with a body-centered cubic (bcc) structure has been studied at high temperatures available to membrane reactors. The permeability of the foil containing 54 wt.% Pd drastically decreases at 625 °C, but it is immediately restored at 600 °C within 1 h. The restoration is probably due to the phase transition from face-centered cubic (fcc) to the bcc structure. In contrast, the permeability gradually decreases at 600 °C with the foil containing 56 wt.% Pd, then gradually recovers at 575 °C. The permeability of the foil containing 60 wt.% Pd also gradually decreases at 500 °C and the formation of the fcc phase partially occurs in the bcc phase accompanying the compositional heterogenization. The permeability of the bcc alloy decreases with a decrease in the Pd content probably due to the decrease in the hydrogen solubility. The activation energy of the H2 permeability increases with the decrease in the Pd content. The permeability gradually decreases after storing the bcc foil under flowing Ar, suggesting that the hydrogen solubility is gradually decreased in the absence of gas-phase hydrogen.