LETTER pubs.acs.org/JPCL
Identifying Metal Alloys with High Hydrogen Permeability Using High Throughput Theory and Experimental Testing Sung Gu Kang,† Kent E. Coulter,‡ Sabina K. Gade,§ J. Douglas Way,§ and David S. Sholl*,† †
School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332-0100, United States ‡ Southwest Research Institute, San Antonio, Texas 78228-0510, United States § Colorado School of Mines, Golden, Colorado 80401, United States
bS Supporting Information ABSTRACT: Dense metal membranes are one useful approach for purifying H2 from mixed gas streams. A longstanding challenge in the development of metal membranes has been to find film compositions that give high permeability for H2 relative to well-known materials such as elemental Pd. We used first-principles calculations to predict the H2 permeability of all disordered alloys of composition Pd96M4. These calculations not only identify the Pdbased alloys that are already known to have favorable membrane properties but also identify as promising a number of materials that have not been previously examined. We tested our predictions by fabricating and testing PdTm films, which, in agreement with our calculations, were found to have good permeability properties for pure H2. SECTION: Energy Conversion and Storage
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arge-scale purification of H2 from fossil fuel or biomass sources could play a key role in efforts to use H2 for transportation fuels and to reduce carbon emissions from power plants.1 Dense metal membranes, which operate by allowing individual H atoms to diffuse through interstitial sites in metal films, are one promising technology for separating H2 from gas streams at elevated temperatures.24 Metal membranes have effectively infinite selectivities for H2 relative to other gases. A key performance metric for comparing metal membranes is their permeability. Pd films have been known for over a century to have high permeability for H2. Most work on metal membranes has focused on finding alloys with higher permeability than Pd that also show improved resistance to contamination. Many binary and ternary alloys have been studied, and a small number of materials with higher permeability than Pd are known.2,4 In particular, PdAg alloys have found practical applications because their H2 permeability is ∼50% higher than Pd. In this Letter, we use quantitative computational modeling to systematically predict that H2 permeability of all Pd-rich FCC binary alloys. We restricted our attention to substitutionally disordered FCC alloys with composition Pd96M4 (in at %). This composition is convenient for the computational modeling described below and allows a wide range of alloying elements to be considered. Some elements do not form solid solutions with Pd at this composition, so this restricts the number of alloying elements we can consider. Fifty elements are known to form solid solutions with Pd at this composition at ∼600 K,5 and we examined all of these elements. r 2011 American Chemical Society
Quantitatively accurate methods already exist for using DFT calculations to predict H2 permeability through individual metal alloys.68 These methods use large collections of site and transitionstate energies for interstitial H to derive lattice models suitable for defining net solubility and diffusion rates. Unfortunately, these methods are very time-consuming, with a typical treatment of one alloy requiring ∼600 individual DFT calculations.68 To make this approach more amenable to screening large numbers of materials, we developed simplified lattice models that were motivated by the results from previous detailed treatments of Pd alloys but can be parametrized with a small number of DFT calculations. Specifically, our simplified models require 12 geometry optimizations with DFT in a supercell containing 27 atoms. This approach was applied to all of the Pd alloys defined above. All DFT calculations were performed with the PW91 generalized gradient approximation functional using the Vienna ab initio simulation package (VASP).20,21 The core electrons of most atoms were described by ultrasoft pseudopotentials (USPPs). For the lanthanides (Ce, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) the projector augmented wave method was used instead because USPPs were unavailable for these elements. Each calculation used a 27-atom supercell with 3 3 3 primitive FCC unit cell with periodic boundary conditions, a plane-wave basis set with Received: October 17, 2011 Accepted: November 16, 2011 Published: November 16, 2011 3040
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The Journal of Physical Chemistry Letters reciprocal space sampled with a 4 4 4 Monkhorst-Pack mesh, and an energy cutoff of 241.622 eV. Geometries were relaxed until the forces on all atoms were 250%). The modeling methods we have used here are well-suited to study more complex materials such as multicomponent alloys8 and ordered compounds,19 so they will be able to play a useful role in future identification of highperformance membrane materials.
’ ASSOCIATED CONTENT
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Supporting Information. Further information on the models and methods. This material is available free of charge via the Internet http://pubs.acs.org
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT This work was funded by the U.S. DOE National Energy Technology Laboratory and Office of Basic Energy Sciences. ’ REFERENCES (1) Ku, A. Y.; Kulkarni, P.; Shisler, R.; Wei, W. Membrane Performance Requirements for Carbon Dioxide Capture Using HydrogenSelective Membranes in Integrated Gasification Combined Cycle (IGCC) Power Plants. J. Membr. Sci. 2011, 367, 233–239. (2) Ockwig, N. W.; Nenoff, T. M. Chemistry of Hydrogen Separation Membranes. Chem. Rev. 2007, 107, 4078. (3) Kamakoti, P.; Morreale, B. D.; Ciocco, M. V.; Howard, B. H.; Killmeyer, R. P.; Cugini, A. V.; Sholl, D. S. Prediction of Hydrogen Flux through Sulfur-Tolerant Binary Alloy Membranes. Science 2005, 307, 569–573. (4) Paglieri, S. N.; Way, J. D. Innovations in Palladium Membrane Research. Sep. Purif. Meth. 2002, 31, 1–169. (5) Massalski, T. B.; Murray, J. L.; Bennett, L. H.; Baker, H. Binary Alloy Phase Diagrams; American Society for Metals: Metals Park, OH, 1986. (6) Semidey-Flecha, L.; Sholl, D. S. Combining Density Functional Theory and Cluster Expansion Methods to Predict H2 Permeance through Pd-Based Binary Alloy Membranes. J. Chem. Phys. 2008, 128, 144701. (7) Semidey-Flecha, L.; Ling, C.; Sholl, D. S. Detailed First-Principles Models of Hydrogen Permeation through PdCu-Based Ternary Alloys. J. Membr. Sci. 2010, 362, 384–392.
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(8) Ling, C.; Semidey-Flecha, L.; Sholl, D. S. First-Principles Screening of PdCuAg Ternary Alloys as H2 Purification Membranes. J. Membr. Sci. 2011, 371, 189–196. (9) Kamakoti, P.; Sholl, D. S. Ab Initio Lattice-Gas Modeling of Interstitial Hydrogen Diffusion in CuPd Alloys. Phys. Rev. B 2005, 71, 014301. (10) Milman, V.; Winkler, B.; White, J. A.; Pickard, C. J.; Payne, M. C.; Akhmatskaya, E. V.; Nobes, R. H. Electronic Structure, Properties, and Phase Stability of Inorganic Crystals: A Pseudopotential PlaneWave Study. Int. J. Quantum Chem. 2000, 77, 895–910. (11) Brodowsky, H.; Poeschel, E. Wasserstoff in Palladium/SilberLegierungen. Z. Phys. Chem. 1965, 44, 143. (12) Knapton, A. G. Palladium Alloys for Hydrogen Diffusion Membranes-a Review of High Permeability Materials. Platinum Met. Rev. 1977, 21, 44–50. (13) Burkhanov, G. S.; Gorina, N. B.; Kolchugina, N. B.; Roshan, N. R.; Slovetsky, D. I.; Chistov, E. M. Palladium-Based Alloy Membranes for Separation of High Purity Hydrogen from Hydrogen-Containing Gas Mixtures. Platinum Met. Rev. 2011, 55, 3–12. (14) Grashoff, G. J.; Pilkington, C. E.; Corti, C. W. The Purification of Hydrogen. Platinum Met. Rev. 1983, 27, 157–169. (15) Sakamoto, Y.; Chen, F. L.; Furukawa, M.; Mine, K. X-ray Studies of the Absorption of Hydrogen by Palladium-Rich Pd-(Tb, Tm, Lu) Alloys. J. Less-Common Met. 1990, 159, 191–198. (16) Subramian, P. R.; Villars, P.; Okamoto, H.; Cenzual, K. H-Tm Phase Diagram; American Society for Metals: Materials Park, OH, 2006. (17) Steward, S. A. Review of Hydrogen Isotope Permeability Through Materials; UCRL-53441; Lawrence Livermore National Laboratory: Livermore, CA, 1983. (18) Fort, D.; Farr, J. P. G.; Harris, I. R. Comparison of PalladiumSilver and Palladium- Yttrium Alloys As Hydrogen Separation Membranes. J. Less-Common Met. 1975, 39, 293–308. (19) Ling, C.; Sholl, D. S. First Principles Investigation of Metal Sulfides As Membranes in Hydrogen Purification. J. Membr. Sci. 2009, 329, 153–159. (20) Kresse, G.; Furthmuller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15–50. (21) Kresse, G.; Hafner, J. Ab-Initio Molecular-Dynamics for OpenShell Transition- Metals. Phys. Rev. B 1993, 48, 13115–13118. (22) Kamakoti, P.; Sholl, D. S. A Comparison of Hydrogen Diffusivities in Pd and CuPd Alloys Using Density Functional Theory. J. Membr. Sci. 2003, 225, 145–154. (23) Coulter, K. E.; Way, J. D.; Gade, S. K.; Chaudhari, S.; Sholl, D. S.; Semidey-Flecha, L. Predicting, Fabricating, And Permeability Testing of Free-Standing Ternary Palladium-Copper-Gold Membranes for Hydrogen Separation. J. Phys. Chem. C 2010, 114, 17173–17180. (24) Gade, S. K.; Thoen, P. M.; Way, J. D. Unsupported Palladium Alloy Foil Membranes Fabricated by Electroless Plating. J. Membr. Sci. 2008, 316, 112–118. (25) Di Pascasio, F.; Gozzi, D.; Panella, B.; Trionfetti, C. H2 Plasma for Hydrogen Loading in Pd. Intermetallics. 2003, 11, 1345–1354. (26) Lemier, C.; Weissmuller, J. Grain Boundary Segregation, Stress and Stretch: Effects on Hydrogen Absorption in Nanocrystalline Palladium. Acta Mater. 2007, 55, 1241–1254. (27) Roa, F.; Way, J. D. The Effect of Air Exposure on PalladiumCopper Composite Membranes. Appl. Surf. Sci. 2005, 240, 85–104. (28) Uchikawa, H.; Okazaki, T.; Sato, K. New Technique of Activating Palladium Surface for Absorption of Hydrogen or Deuterium. Jpn. J. Appl. Phys., Part 1 1993, 32, 5095–5096. (29) Holleck, G. L. Diffusion and Solubility of Hydrogen in Palladium and Palladium-Silver Alloys. J. Phys. Chem. 1970, 74, 503–511.
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