Anomalous Temperature Dependence of Hydrogen Permeability through Palladium–Silver Binary Alloy Membrane and Its Analysis Based on Hydrogen Chemical Potential

Abstract

The hydrogen permeability of Pd-Ag alloy membranes has been investigated over a wide temperature range between 100 C and 500 C. The hydrogen permeation coef cient, Φ, for Pd-23mol%Ag decreases with decreasing temperature above 300 C, in good agreement with the previous literature. However, Φ starts to increases below 250 C, and a peak is observed at around 180 C. Considering the silver concentration and operating temperature, the α-α phase transition never occurs in this condition. In other words, the α-α phase transition is not the reason for the anomalous peak behavior of Pd-23mol%Ag alloy at low temperature. In addition, it is con rmed that the diffusion-limiting hydrogen permeation reaction takes place from room temperature up to 500 C. To understand the reason for the peak appearance, the hydrogen permeability has been analyzed in view of the new description of hydrogen permeation based on hydrogen chemical potential. As a result, it is found that the temperature dependence of the PCT factor, f PCT , is dominant for the peak appearance, meaning that the corresponding pressure-composition-isotherms (PCT curves) are essential for the understanding of hydrogen permeability of the alloy. Dependences of the pressure condition and silver concentration on the peak behavior have also been investigated. The peak temperature increases with increasing the hydrogen pressure at feed side. In addition, the peak appears at lower temperature and becomes remarkable with decreasing silver concentration of Pd-Ag alloy membrane. In other words, the composition of Pd-Ag alloy membranes must be designed based on the operating temperature or pressure condition. Thus, this study suggests new possibilities of alloy design for Pd-Ag alloy membranes.

A Review for Consistent Analysis of Hydrogen Permeability through Dense Metallic Membranes

“…In this paper, three methods are reviewed: (a) pressure-dependent hydrogen permeation coefficient [15,[19][20][21], (b) analysis of hydrogen diffusivity based on thermodynamic factor [22][23][24][25], and (c) consistent description of hydrogen permeability based on hydrogen chemical potential [26]. Four examples of the application of the consistent description of hydrogen permeability are introduced: (a) prediction of hydrogen flux under given conditions, (b) comparability of hydrogen permeability with the hydrogen permeation coefficient for the power law, (c) understanding of the anomalous temperature dependence of hydrogen permeability found recently in Pd-Ag alloy membranes [27], and (d) alloy design of V-based alloy membranes with high hydrogen permeability and strong resistance to hydrogen embrittlement [28].…”

Hydrogen and Deuterium Solubility in Commercial Pd–Ag Alloys for Hydrogen Purification

“…Many studies about bulk Pd-membranes are devoted to the investigation of the permeability as a function of temperature [16][17][18][19][20], which is the physical quantity of principal interest for applications. Less attention has been devoted to the solubility of hydrogen in Pd-Ag alloys, which however gives important information about the physical state of the alloys.…”

Quantitative Evaluation of Hydrogen Solubility and Diffusivity of V–Fe Alloys toward the Design of Hydrogen Permeable Membrane for Low Operative Temperature

“…Figure 4 shows the time dependence of the normalized hydrogen ux, J L, for V-10Fe alloy membrane under the given condition mentioned above. For comparison, the value of the normalized hydrogen ux for Pd-23mol%Ag alloy membrane at the same condition is estimated from the previous study 26) and drawn in the gure by a broken line. As shown in Fig.…”

“…It is well known that the addtion of silver into palladium suppresses the α-α phase trainsition by lowering critical temperature. For (Pd-27mol%Ag)-H pseudobinary system, the critical temperature of α-α phase trainsition is about 244 K 26) . Thus, the overlayer of Pd-27mol%Ag alloy is considered to be more suitable than that of pure Pd at low operative temperature.…”

“…Thus, the new description of hydrogen permeability expressed by eq. (1) is applicable to not only Nb-based 16,17) and Pd-based 18,26) alloy membrane, but also V-based alloy membrane.…”