Solubility of Hydrogen in PdAg and PdAu Binary Alloys Using Density Functional Theory

Abstract

The present work deals with the study of palladium-silver (PdAg) and palladium-gold (PdAu) binary alloys over a broad range of temperatures and alloy compositions using density functional theory (DFT) to find possible conditions where the solubility of hydrogen (H) is significantly higher than that of pure palladium (Pd). Several alloy structures, such as Pd(100-x)Ag(x) with x = 14.81, 25.93, 37.04, and 48.51, Pd(100-x)Aux with x = 14.81, 25.93, and 37.04, and Pd(100-x)Cu(x) with x = 25.93 and 48.51 were considered. The lattice constants of these structures were optimized using DFT, and relaxed structures were used for the estimation of binding energy. It was found that the solubility of H in PdAg is higher than pure Pd with a maximum at approximately 30% Ag at 456 K. Also, the solubility of PdAu alloys was higher than pure Pd with a maximum at about 20% Au with a solubility 12 times higher than that of pure Pd. It was found that for a 3.7% H concentration in a PdAg alloy, a cell expansion of 0.15-0.2% occurs, which if ignored may affect the individual binding energy of the O-site by approximately 3.56% and may affect the predicted solubility by approximately 11.8%.

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

“…These improvements are in particular of importance for high concentrations of alloying elements and for alloying elements that strongly interact with H. This is because under such conditions linear dependency of input parameters breaks down and preferred occupation of tetrahedral sites could occur, as recently indicated by ab initio calculations. [32] These extensions of the model as well as taking the vibrational contributions into account are under consideration.…”

Atom configurations in Pd–Au and Pd–Au–D alloys: A neutron total scattering and Reverse Monte Carlo study

“…In the Pd 75 Au 25 -D 33 Vac 67 sample the O sites with 2 nn and 8 nnn Au atoms (RMC average configuration) are more favorable for D than the O sites with 1.5 nn and 2 nnn Au atoms (average for a random configuration). First-principles calculations [4,5] of the hydrogen binding energy on octahedral sites with different metal nn and nnn coordination shells support this statement. Hydrogen binding energies estimated based on Ref.…”

“…Our results regarding the simultaneous occupation of O and T sites are in agreement with those from theoretical studies on hydrogen in Pd alloys which infer that the occupation of tetrahedral sites may occur depending on the alloying element and its concentration. For example, first-principles studies on hydrogen in PdAg [4][5][6] and Pd-Au alloys [4,5] suggest that the O site is preferred when most of the neighbors are palladium atoms, while the T site is preferred when the alloying element dominates. First-principles calculations also show that the site occupancy and stability is actually determined by the local atomic arrangement of metal atoms in the nearest neighborhood of the interstitial site [4][5][6][7][8].…”

Mathematical Modeling of an Integrated Membrane Reactor for Methane Steam Reforming

“…Experimental studies and DFT-based calculations how that Pd in binary or ternary alloys improves the permeability of the membranes [27,28]. In particular, Au or Ag can increase the permeability of the alloy of up to 5 times respect to Ni, Rh, Pt [29]. The hydrogen permeates selectively a wall of membrane accordingly to the Sieverts' law.…”