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Membranes 2018, 8(3), 82; https://doi.org/10.3390/membranes8030082

Thermodynamic Aspects in Non-Ideal Metal Membranes for Hydrogen Purification

1
Department of Environmental and Chemical Engineering (DIATIC), University of Calabria, Via P. Bucci, Cubo 44A, 87036 Rende, Italy
2
Institute for International Collaboration, Hokkaido University, Sapporo, Hokkaido 060-0815, Japan
3
Department of Chemistry, Faculty of Science, Hokkaido University, N10W8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan
4
Inorganic Membranes and Membrane Reactors (SIR), Sustainable Process Engineering (SPE), Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, STW 1.45, 5600 MB Eindhoven, The Netherlands
*
Authors to whom correspondence should be addressed.
Received: 14 August 2018 / Revised: 10 September 2018 / Accepted: 10 September 2018 / Published: 16 September 2018
(This article belongs to the Special Issue Pd-based Membranes: Overview and Perspectives)
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Abstract

In this paper, an overview on thermodynamic aspects related to hydrogen-metal systems in non-ideal conditions is provided, aiming at systematically merging and analyzing information achieved from several different studies present in the open literature. In particular, the relationships among inner morphology, dissolved hydrogen and internal stresses are discussed in detail, putting in evidence the conformation complexity and the various types of dislocations induced by the presence of H-atoms in the lattice. Specifically, it is highlighted that the octahedral sites are preferentially occupied in the FCC metals (such as palladium), whereas tetrahedral sites are more energetically favored in BCC-structured ones (such as vanadium). These characteristics are shown to lead to a different macroscopic behavior of the two classes of metals, especially in terms of solubility and mechanical failure due to the consequent induced stresses. Furthermore, starting from the expression of the chemical potential generally presented in the literature, a new convenient expression of the activity of the H-atoms dissolved into the metal lattice as a function of the H-concentration is achieved. Such an activity expression is then used in the dissolution equilibrium relationship, which is shown to be the overall result of two different phenomena: (i) dissociative adsorption of molecular hydrogen onto the surface; and (ii) atomic hydrogen dissolution from the surface to the metal bulk. In this way, the obtained expression for equilibrium allows a method to calculate the equilibrium composition in non-ideal conditions (high pressure), which are of interest for real industrial applications. View Full-Text
Keywords: chemical potential; activity; hydrides; solubility; membranes chemical potential; activity; hydrides; solubility; membranes
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Bellini, S.; Sun, Y.; Gallucci, F.; Caravella, A. Thermodynamic Aspects in Non-Ideal Metal Membranes for Hydrogen Purification. Membranes 2018, 8, 82.

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