Three+three for free: Sulfur Poisoning

“In every tyrant's heart there springs in the end this poison, that he cannot trust a friend” -- Aeschylus (Ancient Greek Dramatist and Playwright known as the founder of Greek tragedy, 525 BC-456 BC)

These six items are available for free download on the Web.  One is a patent.  The others are journal articles.  This is not a substitute for an in-depth online literature search, of course.  I like to think of free downloads as analogous to browsing in a bookstore.  It’s fun to make accidental discoveries.  You never know when you will happen on something really interesting.

///////
Title: Method for preparing a palladium-gold alloy gas separation membrane system (Shell)

Type	Patent
Inventor	Earl PERKINS II Nathan
Inventor	John Charles Saukaitis
URL	Free Full Text Source:  http://www.google.com/patents/US8721773
Assignee	Shell Oil Company
Patent Number	US8721773 B2
Issue Date	May 13, 2014
Abstract	A method for preparing a palladium-gold alloy gas separation membrane system comprising a gold-palladium alloy membrane on a porous substrate coated with an intermetallic diffusion barrier. The method includes an abrading step to increase surface roughness of the palladium to a desired range, a gold plating step with a solution of chloroauric acid (AuCl4H) and hydrogen peroxide, followed by annealing to produce a palladium-gold alloy membrane.

Title: Chemical imaging of the sulfur-induced deactivation of Cu/ZnO catalyst bodies

Type	Journal Article
Author	Andrew M. Beale
Author	Emma K. Gibson
URL	Free Full Text Source:  http://www.sciencedirect.com/science/article/pii/S0021951714000876
Volume	314
Pages	94-100
Publication	Journal of Catalysis
Date	May 2014
Abstract	The effects of sulfur poisoning on the water–gas shift (WGS) activity of industrial Cu/ZnO/Al2O3 catalyst bodies have been studied. The samples were characterized using chemical imaging methods, including XRD-CT, XAFS mapping, and XRF, in order to understand the process by which accelerated sulfur poisoning leads to catalyst deactivation. After ∼90 h on stream, all catalysts exhibited reduced activity; the higher the H2S concentration, the greater the extent of deactivation. Non-invasive XRD-CT measurements performed on intact samples recovered from the reactor revealed the formation of sulfide phases, including sphalerite (β-ZnS) and crystalline CuS, Cu2S, and CuSO4 phases. These sulfide phases were distributed predominantly as a graduated corona around the sample edge reaching ∼1.5 mm thick for experiments performed in the highest concentration of 500 ppm H2S. XAFS mapping, which is particularly sensitive to the local coordination environment around the element being probed, confirmed the presence of mixed Cu/Zn–O/S coordination environments and that the core of the sample remained sulfur-free. A combination of XRD-CT and XRF revealed that CuS appeared to be mobile under reaction conditions resulting in the redistribution of Cu toward the very edge of the samples. A combination of techniques has therefore demonstrated that H2S deactivation of Cu/ZnO/Al2O3 catalyst bodies occurs via phase transformation of the active Cu/ZnO phase into sulfides and redistribution of these components over the sample instead of Cu active site poisoning by Sads species.

Title: Elementary Kinetic Numerical Simulation of Ni/YSZ SOFC Anode Performance Considering Sulfur Poisoning

Type	Journal Article
Author	Matthias Riegraf
Author	Günter Schiller
URL	Free Full Text Source:  http://jes.ecsdl.org/content/162/1/F65
Volume	162
Issue	1
Pages	F65-F75
Publication	Journal of The Electrochemical Society
Date	01/01/2015
Journal Abbr	J. Electrochem. Soc.
Abstract	An elementary kinetic model is developed and applied to explore the influence of sulfur poisoning on the behavior of solid oxide fuel cell (SOFC) anodes. A detailed multi-step reaction mechanism of sulfur formation and oxidation at Ni/YSZ anodes together with channel gas-flow, porous-media transport and elementary charge-transfer chemistry is established for SOFCs operating on H2/H2O mixtures with trace amounts of hydrogen sulfide (H2S). A thermodynamic and kinetic data set is compiled from various literature sources. The derived chemical model, validated against sulfur chemisorption isobars taken from literature, is used to analyze performance drops of SOFCs working under typical fuel cell operating conditions. Electrochemical results show that at relatively low H2S concentrations SOFC button-cell performance can be interpreted using chemical sulfur formation. However, when the concentration is sufficiently high, the inclusion of second stage degradation and triple-phase boundary reconstruction is necessary to describe the performance decrease. Additionally, it is shown that the sulfur surface coverage increases with increasing current density. In order to shed more light on advanced fundamental understanding of cell poisoning, sensitive analyses toward total anode resistance and sulfur coverage for different operating conditions were performed.

Title: Sulfur Poisoning of SOFC Anodes: Effect of Overpotential on Long-Term Degradation

Type	Journal Article
Author	A. Hauch
Author	A. Hagen
URL	Free Full Text Source:  http://jes.ecsdl.org/content/161/6/F734
Volume	161
Issue	6
Pages	F734-F743
Publication	Journal of The Electrochemical Society
Date	01/01/2014
Journal Abbr	J. Electrochem. Soc.
Abstract	Sulfur impurities in carbon containing fuels for solid oxide fuel cells (SOFC), e.g. natural gas and biogas, typically lead to significant losses in performance due to the sulfur sensitivity of Ni/yttria-stabilized-zirconia (YSZ) anodes for SOFC. Full cells having Ni/YSZ anodes have been characterized during long-term galvanostatic operation in internal reforming gas mixture (CH4/H2O/H2:30/60/10), with 2 ppm H2S exposure to the anode for 500 hours at 850°C, at different current densities. This work focus on the long-term effect of H2S exposure over a few hundreds of hours; and describes and correlates the observed evolution of anode performance, over hundreds of hours, with sulfur exposure at low cell overpotential (low current density) and at high overpotential (high current density) with and without H2S exposure. For tests at low overpotential with H2S exposure only a reversible loss in performance was observed and post-mortem SEM analysis showed an intact Ni/YSZ anode microstructure. For tests at high cell overpotential the H2S exposure caused both a reversible loss in performance and an irreversible long-term degradation. Post-mortem SEM analysis of the Ni/YSZ anode from this tests showed increased porosity and lack of percolating Ni in the few microns of the anode closest to the anode/electrolyte interface.

Title: Sulfur Poisoning of SOFCs: A Model Based Explanation of Polarization Dependent Extent of Poisoning

Type	Journal Article
Author	Vinod M. Janardhanan
Author	Dayadeep S. Monder
URL	Free Full Text Source:  http://jes.ecsdl.org/content/161/14/F1427
Volume	161
Issue	14
Pages	F1427-F1436
Publication	Journal of The Electrochemical Society
Date	01/01/2014
Abstract	Several experimental studies have shown that, 1) the extent of the poisoning effect due to trace amounts of sulfur compounds in the fuel is lower if a SOFC is operated at a higher current density, and 2) the performance drop due to sulfur poisoning is much lower for Ni-GDC or Ni-ScSZ anodes when compared to Ni-YSZ anodes. This work presents a first principles numerical model that simulates experimental studies of sulfur poisoning on SOFC button cells. The exchange current densities for the electrodes are determined using sulfur-free polarization data for cells fueled by humidified mixtures of H2 and N2. A detailed surface reaction model that predicts the fractional coverage of all adsorbed species at the three phase interface is coupled to the SOFC model and the sulfur coverage is used to alter the anode exchange current density. The resulting model predictions match experimental observations during both galvanostatic and potentiostatic operation. Our analysis shows that the observed lower performance drop at higher current density is due to the non-linear nature of the electrochemical rate equations, and that the lower impact of sulfur poisoning on Ni-GDC and Ni-ScSZ anodes (compared to Ni-YSZ anodes) is due to their higher electrochemical activity.

Title: Three-Dimensional Microstructural Imaging of Sulfur Poisoning-Induced Degradation in a Ni-YSZ Anode of Solid Oxide Fuel Cells

Type	Journal Article
Author	William M. Harris
Author	Jeffrey J. Lombardo
URL	Free Full Text Source:  http://www.nature.com/srep/2014/140610/srep05246/full/srep05246.html?message-global=remove
Volume	4
Publication	Scientific Reports
Date	June 10, 2014
Journal Abbr	Sci. Rep.
Abstract	Following exposure to ppm-level hydrogen sulfide at elevated temperatures, a section of a solid oxide fuel cell (SOFC) Ni-YSZ anode was examined using a combination of synchrotron-based x-ray nanotomography and x-ray fluorescence techniques. While fluorescence measurements provided elemental identification and coarse spatial mapping, x-ray nanotomography was used to map the detailed 3-D spatial distribution of Ni, YSZ, and a nickel-sulfur poisoning phase. The nickel-sulfur layer was found to form a scale covering most of the exposed nickel surface, blocking most fuel reformation and hydrogen oxidation reaction sites. Although the exposure conditions precluded the ability to develop a detailed kinetic description of the nickel-sulfur phase formation, the results provide strong evidence of the detrimental effects of 100 ppm hydrogen sulfide on typical Ni-YSZ anode materials.