Towards Designing Stable Pd‐Based Membranes for Hydrogen Gas Separation: A Statistical Thermodynamics Approach

Abstract

A method to design new, not yet synthesized, multicomponent alloys based on knowledge of binary alloys is applied to develop Pd‐alloys for membranes for gas separation. The approach couples the cluster variation method with effective pair potentials to describe the phase boundaries between the α‐solid solution (low hydrogen content) and β‐hydride phases. The calculations illustrate (i) that the method can predict α − β phase boundaries of hydrogen in binary and ternary Pd‐alloys, (ii) how the relative interaction strengths of filled and empty interstitial sites influence the width of the miscibility gap, (iii) that the hydrogen absorption capacity of an alloy is related to the hydride phase stability and (iv) the presence of short range order of hydrogen in β‐hydrides.

Phase stabilities of Pd-based alloys for membranes for hydrogen gas separation: A statistical thermodynamics approach

“…1 demonstrate that the model is able to describe the effect of the choice of the alloying element (Ni and Rh) and its concentration on the phase boundaries. Similar results were obtained for the case of other Pd-M-H systems; some examples will be discussed in [12]. The analysis of the values of the L-J parameters used to calculate the phase boundaries in Pd (100−x) Ni x -H and Pd (100−x) Rh x -H systems shows that the strength of the effective field of the metal sublattice and the relative interaction strength between nearest-neighbor occupied (H) and unoccupied (Vac) interstitial sites determine the phase boundaries (see Table 1).…”

“…Due to space limitation we will discuss just a few examples, more results and further applications will be described in [12].…”

“…An 8-4 type Lennard-Jones (L-J) potential is used to describe the volume dependence of the effective pair interactions [7]. The L-J parameters describing the H-H and Vac-Vac effective pair interactions are determined based on the cohesive energies and lattice parameters of, respectively, the fully hydrogenated and the hydrogen free alloys as described in [12]. The parameters describing the H-Vac effective pair interactions are obtained by fitting to the phase boundaries, i.e.…”

High throughput screening of Pd-alloys for H2 separation membranes studied by hydrogenography and CVM

“…alloying the Pd, but given the amount of alloying elements and compositions which need to be screened this is not a trivial task. For PdeCu and PdeAg alloys it is known that the T c decreases as function of increasing Cu and Ag concentration [13,14]. Furthermore, these alloys have the additional advantage of being more resistant towards contaminations [5,15e17] and having a sufficient or even improved permeability as compared to pure Pd [3e5,18e20] while the reduction of the amount of Pd results also in a cost benefit [21,22].…”

“…Here we show its applicability to determine the critical temperature of promising multi-component Pd-alloys for hydrogen separation membranes. In addition, we combine the thin film hydrogenography technique with the cluster variation method (thermodynamic CVM calculations) based on input of data from binary (bulk) alloys [14]. This coupled approach enables us to identify candidate alloys and examine their hydrogenation properties around the critical point.…”