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Title: Segregation at CuxPd1-x alloy hydrogen purification membranes

Abstract

CuxPd1-x alloy membranes have exhibited sulfur tolerance in their application as hydrogen purification membranes. The surfaces of such membranes are known to have compositions that differ from those of the bulk and furthermore, compositions that vary with environment. XPS, LEIS and hydrogen adsorption have been used to characterize the surfaces of a Cu30Pd70 membrane over temperatures ranging from 300 – 1000 K. On timescales of ~1 hour, the surface is found to equilibrate with the near surface region at all temperatures above 300 K but is only equilibrated with the bulk at temperatures in excess of 800 K. The clean alloy surface is Cu rich, but once modified by the adsorption of sulfur the surface exposes only Pd.

Authors:
; ; ;
Publication Date:
Research Org.:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, and Morgantown, WV
Sponsoring Org.:
USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
913197
Report Number(s):
DOE/NETL-IR-2007-096
TRN: US200802%%592
DOE Contract Number:
None cited
Resource Type:
Conference
Resource Relation:
Conference: ACS 233rd National Meeting, Chicago, IL, Mar. 25-29, 2007
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ADSORPTION; ALLOYS; HYDROGEN; MEMBRANES; PURIFICATION; SEGREGATION; SULFUR; TOLERANCE; X-RAY PHOTOELECTRON SPECTROSCOPY

Citation Formats

Gellman, A.J., Ye, P., Miller, J.B., and Matranga, C.S. Segregation at CuxPd1-x alloy hydrogen purification membranes. United States: N. p., 2007. Web.
Gellman, A.J., Ye, P., Miller, J.B., & Matranga, C.S. Segregation at CuxPd1-x alloy hydrogen purification membranes. United States.
Gellman, A.J., Ye, P., Miller, J.B., and Matranga, C.S. Thu . "Segregation at CuxPd1-x alloy hydrogen purification membranes". United States. doi:.
@article{osti_913197,
title = {Segregation at CuxPd1-x alloy hydrogen purification membranes},
author = {Gellman, A.J. and Ye, P. and Miller, J.B. and Matranga, C.S.},
abstractNote = {CuxPd1-x alloy membranes have exhibited sulfur tolerance in their application as hydrogen purification membranes. The surfaces of such membranes are known to have compositions that differ from those of the bulk and furthermore, compositions that vary with environment. XPS, LEIS and hydrogen adsorption have been used to characterize the surfaces of a Cu30Pd70 membrane over temperatures ranging from 300 – 1000 K. On timescales of ~1 hour, the surface is found to equilibrate with the near surface region at all temperatures above 300 K but is only equilibrated with the bulk at temperatures in excess of 800 K. The clean alloy surface is Cu rich, but once modified by the adsorption of sulfur the surface exposes only Pd.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}

Conference:
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  • X-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEISS) have been used to study the effects of various surface preparations and thermal treatments on the composition of the near-surface region (~7 atomic layers) and the topmost atomic layer of a polycrystalline Pd70Cu30 alloy. Palladium enrichment (relative to the bulk composition) is observed in the XPS-accessible near-surface region, but copper enrichment is observed in the topmost atomic layer. At temperatures above ~800 K, where the bulk, the near-surface region and the topmost atomic layer are likely in thermodynamic equilibrium, segregation to the top layer can be described in termsmore » of a simple thermodynamic model. Temperature programmed desorption (TPD) of H2 and CO from the annealed surfaces illustrates the impact of segregation and atomic distribution in the top layer on surface chemical activity.« less
  • X-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEISS) have been used to study the effects of various surface preparations and thermal treatments on the composition of the near-surface region (~7 atomic layers) and the topmost atomic layer of a polycrystalline Pd 70Cu 30 alloy. Palladium enrichment (relative to the bulk composition) is observed in the XPS-accessible near-surface region, but copper enrichment is observed in the topmost atomic layer. At temperatures above similar to 800 K, where the bulk, the near-surface region and the topmost atomic layer are likely in thermodynamic equilibrium, segregation to the top layer canmore » be described in terms of a simple thermodynamic model. Temperature programmed desorption (TPD) of H 2 and CO from the annealed surfaces illustrates the impact of segregation and atomic distribution in the top layer on surface chemical activity.« less
  • Development of advanced hydrogen separation membranes in support of hydrogen production processes such as coal gasification and as front end gas purifiers for fuel cell based system is paramount to the successful implementation of a national hydrogen economy. Current generation metallic hydrogen separation membranes are based on Pd-alloys. Although the technology has proven successful, at issue is the high cost of palladium. Evaluation of non-noble metal based dense metallic separation membranes is currently receiving national and international attention. The focal point of the reported work was to evaluate two different classes of materials for potential replacement of conventional Pd-alloy purification/diffusermore » membranes. Crystalline V-Ni-Ti and Amorphous Fe- and Co-based metallic glass alloys have been evaluated using both electrochemical and gaseous hydrogen permeation testing techniques..« less
  • Development of advanced hydrogen separation membranes in support of hydrogen production processes such as coal gasification and as front end gas purifiers for fuel cell based system is paramount to the successful implementation of a national hydrogen economy. Current generation metallic hydrogen separation membranes are based on Pd-alloys. Although the technology has proven successful, at issue is the high cost of palladium. Evaluation of non-noble metal based dense metallic separation membranes is currently receiving national and international attention. The focal point of the reported work was to evaluate two different classes of materials for potential replacement of conventional Pd-alloy purification/diffusermore » membranes. Crystalline V-Ni-Ti and Amorphous Fe- and Co-based metallic glass alloys have been evaluated using gaseous hydrogen permeation testing techniques.« less
  • Separation of hydrogen from mixed gas streams is an important step for hydrogen generation technologies, including hydrocarbon reforming and coal/biomass gasification. Dense palladium-based membranes have received significant attention for this application because of palladium’s ability to dissociatively adsorb molecular hydrogen at its surface for subsequent transport of hydrogen atoms through its bulk. Alloying palladium with minor components, like copper, has been shown to improve both the membrane’s structural characteristics and resistance to poisoning of its catalytic surface [1]. Surface segregation—a composition difference between the bulk material and its surface—is common in alloys and can affect important surface processes. Rational designmore » of alloy membranes requires that surface segregation be understood, and possibly controlled. In this work, we examine surface segregation in a polycrystalline Pd70Cu30 hydrogen separation membrane as a function of thermal treatment and adsorption of hydrogen sulfide.« less