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

Abstract

A concept for alloy design of hydrogen permeable membrane with high hydrogen permeability and long-term durability has been proposed in view of the PCT factor, f PCT , and the ductile-to-brittle transition hydrogen concentration, DBTC. As an example, V-10mol%Fe alloy has been designed for low operative temperature, which exhibits excellent and stable hydrogen permeability for at least 1000 hours at 573 K without brittle fracture.In addition, the alloying effects of iron on the hydriding property and the hydrogen diffusivity have been investigated quantitatively in order to establish a way to design optimal composition of V-Fe based hydrogen permeable alloy under any given conditions. It is found that the addition of iron into vanadium increases linearly the partial molar enthalpy change, ∆H 0.2 , of hydrogen for hydrogen dissolution, but scarcely affects on the partial molar entropy change, ∆S 0.2 . It is also found that both the activation energy, E and the pre-exponential factor, B 0 , of the mobility for hydrogen diffusion decrease linearly with increasing the mole fraction of iron, meaning that the addition of iron enhances the hydrogen diffusivity at low temperature below about 700 K. The evaluation in view of the four parameters, ∆H 0.2 , ∆S 0.2 , E and B 0 , is useful for deep understanding of the property of hydrogen permeable metal membrane. Following the concept for alloy design in view of these four parameters, optimal alloy composition can be designed under any given conditions. The hydrogen permeability of the designed alloy under the condition can also be estimated quantitatively.

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

“…Suzuki et al showed that the hydrogen diffusivity (B) and solubility (f PCT ), which contribute to the hydrogen flux (J) directly, can be separately analyzed using Equation (18), as stated in Section 3. The validity of Equation (18) has been confirmed by the permeation tests for Pd-, Nb-, and V-based alloy membranes [26][27][28][29][30][31][32]. For example, the changes in the hydrogen flux through a pure Nb membrane is measured at 400 • C with different pressure conditions.…”

“…Membranes 2020, 10, x FOR PEER REVIEW 3 of 21 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].…”

“…In this section, an example of the application of the consistent description will be reviewed, focusing on the alloy design of V-Fe alloy membrane with high hydrogen permeability together with strong resistance to hydrogen embrittlement [28].…”

“…Here, a concept for alloy design to enhance hydrogen flux while suppressing hydrogen concentration below the DBTC will be discussed in view of the PCT factor. Figure 13 shows the schematic illustration of PCT curves showing the concept for alloy design [28]. Based on Equation 18, there are three ways to enhance hydrogen flux: (1) increase the difference of hydrogen concentrations between the feed and permeation sides (integral interval, c 2~c1 ), (2) increase the hydrogen concentration (c), i.e., operate under a high hydrogen concentration condition, and (3) increase the slope of the PCT curve (dln(P/P 0 )/dc).…”

“…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].…”