Diffusion coefficient of hydrogen in a Pd‐Ag membrane: Effect of hydrogen solubility

Abstract

The permeabilities of hydrogen through a Pd,,-Ag,, membrane have been measured at temperatures ranging from 423 to 573 K and under hydrogen pressure differences ranging from 69 to 256 kPa. From the available literature solubility data a neural network model has been developed in order to simulate the variation of the hydrogen content in the alloy as a function of pressure and temperature. Then, from steady state permeability measurements and calculated solubilities, the diffusion coefficients of hydrogen have been computed. At a given temperature, the diffusion coefficient has been found to decrease with the hydrogen content (0.1 I n = H/M s 0.37). A simple relation is then suggested to predict the variation of the diffusion coefficient on both temperature and hydrogen content. To account for the variation of the diffusion coefficient with n, the integration of Fick's law of diffusion has been performed numerically, resulting in non-linear profile of hydrogen content through the membrane under steady state permeation.On a mesurk la permkabilitk de I'hydrogtne dans une membrane de Pd,5-Ag2S h des temp6ratures comprises entre 423 et 573 K et h des differences de pression d'hydrogtne variant de 69 h 256 P a . A partir des donnks de solubilitk de la litttrature scientifique, on a mis au point un modtle de rkseau neuronal afin de simuler la variation de la teneur en hydrogtne dans I'alliage en fonction de la pression et de la temp&ature. Puis, h partir de mesures de permkabilitk h l'ktat permanent et de calculs de solubilitks, on a calculk par ordinateur les coefficients de diffusion de I'hydroghe. On a observk qu'h une temp6rature donnke le coefficient de diffusion diminuait avec la teneur en hydrogtne (0,l 5 n = H/M 5 0,37). Une relation simple est ensuite suggkrke pour praire la variation du coefficient de diffusion par rapport h la temp6rature et la teneur en hydrogtne. Afin de tenir compte de la variation du coefficient de diffusion avec n, la loi de diffusion de Fick a ktk intkgrke numkriquement. Le rksultat est un profil non linkaire de la teneur en hydrogtne dans la membrane dans des conditions de permkation h l'ktat permanent.Keywords: diffusion of hydrogen, Pd-Ag membrane, hydrogen permeation, hydrogen solubility. alladium-silver membranes are well known for their

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

“…Instead, these approaches have used the approximation of representing the PdAg alloy as a cluster of 4 atoms in a face-centered cubic (fcc) arrangement with or without periodic boundary conditions. A system and approach used by these researchers − does not provide the flexibility of estimating binding energy as well as solubility of PdAg and PdAu alloys with intermediate alloy compositions, hydrogen concentrations, and operating conditions (temperature, pressure) to find a suitable system composition and operating conditions for higher solubility. In addition, the errors associated with neglecting the effect of lattice expansion due to H on the binding energy/solubility are completely ignored under the assumption that they are negligible.…”

Hydrogen Absorption in Pd–Ag Systems: A TPD and Electrical Resistivity Study

“…The Pd–Ag resistivity measured in hydrogen (Figure 3) can be now overlapped by that obtained after the vacuum/desorption process at different absorption temperatures. Here, H/M was extrapolated by the literature data on the same kind of alloy [11,18,19,20,21,22]. By moving from right to left of the graph in Figure 8, i.e., following the temperature decrease starting from 450 °C, it is observed that: (1) in region A below 450 °C, the resistivity ρ i increases until a maximum was reached at ~200 °C, (2) in region B, a decrease is observed until a minimum in resistivity is reached at ~110 °C, and (3) in region C, there is a continuous increase of resistivity.…”

Pd-Ag Electrical Resistivity in Hydrogen and Deuterium: Temperature Effect

“…In this study, both H/M [22,30,40,42,43,44] and D/M [18,21,22,23,31,45] were extrapolated by literature data on the same kind of alloy in order to compare solubility with resistivity data. The literature evidenced that at 100 kPa for low temperatures (25–70 °C) the D/M approaches the H/M value, while increasing the temperature (75–200 °C) causes the D/M to decreases faster, and only at high temperature (>300 °C) do both curves (H and D) tend to converge to very low values (close to zero).…”