Abstract
It is generally understood that the hydrogen permeability of Pd-Ag alloy membranes declines with decreasing temperature. However, recent studies have revealed that the hydrogen permeability of Pd-Ag alloy membranes inversely increases at a certain temperature range and reaches a peak. The peak behavior reflects the shape of pressure-composition isotherms (PCT curves). In order to elucidate the relationship between the reverse temperature dependence of hydrogen permeability and the PCT curves, the hydrogen permeability of pure Pd and Pd-X (X = Ho, Y, and Ni) alloy membranes were investigated. The pure Pd and Pd-5 mol%Ni alloy membranes, in which the α-α’ phase transition occurs, exhibits more significant peak behaviors than Pd-5 mol%Ho, Pd-5 mol%Y, and Pd-23 mol%Ag alloy membranes, in which the α-α’ phase transition is suppressed. Large differences in hydrogen solubility, at the hydrogen pressures above and below the plateau region or the inflection point, make the peak behaviors more significant. It is revealed that the peak temperature can be roughly predicted by the hydrogen pressure at the plateau regions or the inflection points in the PCT curves.
Highlights
Effective utilization of hydrogen energy is required to realize one of the sustainable development goals (SDGs) for 2030 adopted by the United Nations Summit, “SDG 7 affordable and clean energy” [1]
Results the hydrogen permeation coefficient of Pd-23 mol%Ag alloy membrane is shown in the figure [18]
The significant and discontinuous peak behaviors of the hydrogen permeability for pure Pd were caused by the α-α’ phase transition (Figures 5 and 6)
Summary
Effective utilization of hydrogen energy is required to realize one of the sustainable development goals (SDGs) for 2030 adopted by the United Nations Summit, “SDG 7 affordable and clean energy” [1]. The hydrogen gas can be produced by various processes, including the steam reforming [2], dissolution reactions of biomass [3], and the electrolysis of water [4]. The produced gas always contains impurity gas other than hydrogen and needs to be purified before supplied to fuel cells [5]. Hydrogen permeable dense metallic membranes can separate and purify hydrogen gas with ultra-high purity [6]. Pd-based alloys such as Pd-Ag and Pd-Cu alloys are known as materials used for the hydrogen permeable dense metallic membranes [6,7]. Shirasaki et al investigated the hydrogen permeability of various Pd-based alloy membranes at high temperatures [8]. Sakamoto et al reported that Pd-Y and Pd-Ag-Y alloy membranes exhibit higher hydrogen permeability than pure Pd and
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