The effect of current density on H2S-poisoning of nickel-based solid oxide fuel cell anodes

Brightman, Edward; Ivey, Douglas G.; Brett, Dan J. L.; Brandon, Nigel P.

doi:10.1016/j.jpowsour.2010.09.089

Cited by 96 publications

(84 citation statements)

References 17 publications

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“…3,13,14 These studies, among others, have suggested that the increased flux of O 2− ions at the TPB due to the Figure 12. Anode polarization resistance before and after poisoning as a function of cell current density.…”

Section: Resultsmentioning

confidence: 96%

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

Janardhanan

Monder

2014

J. Electrochem. Soc.

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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 H 2 and N 2 . 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. Solid oxide fuel cell (SOFC) systems operating on natural gas or gasified coal can be significantly more energy efficient than today's combustion systems and can thus reduce CO 2 emissions. However, a major problem associated with the use of hydrocarbon fuels is the presence of sulfur containing compounds that are converted to H 2 S under SOFC operating conditions.1 The H 2 S present in the feed gas can readily deactivate conventional Ni cermet anodes. One can certainly have a desulfurization unit before the fuel cell stack to deal with the sulfur poisoning. However, this leads to increased system complexity and decrease in overall efficiency. Nevertheless, it is important to understand and quantify the sulfur tolerance of SOFC anodes in the event of sulfur breakthrough from the desulfurizer. Sulfur poisoning of Ni-YSZ anodes in SOFC is well studied experimentally for model fuel compositions consisting of ppm levels of H 2 S in mixtures of H 2 , H 2 O and an inert 2-4 as well as H 2 S in gas mixtures representative of natural gas or reformed natural gas.5-8 Most of the experimental literature deals with H 2 S concentrations well below 10 ppm and work that treats H 2 S concentrations higher than 20 ppm is rather limited. 2,5,8 On the other hand it is well known that natural gas and biogas can have substantially higher sulfur concentrations and that catalytic steam reforming of methane can be carried out on Ni even with 100 ppm H 2 S without losing all catalytic activity 9,10 e.g., a methane conversion (in model biogas) of ∼35% can be maintained using a supported Ni catalyst with 100 ppm H 2 S at 800• C. 10For an electrolyte supported cell Zha et al., 2 studied the cell performance for a wide range of H 2 S concentrations using DC polarization and electrochemical i...

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Section: Resultsmentioning

confidence: 96%

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

Janardhanan

Monder

2014

J. Electrochem. Soc.

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“…Another important detail is that there was no thermodynamic equilibrium in the studied system at working conditions, and only steady state conditions (flowing gas feeds and flow of oxide ions through the fuel cell membrane) have been established. Different studies proposed and supported experimentally the idea that the release of sulphur from SOFC electrode might take place through the oxidation of sulphur [10,18,22,23,29], which premises the presence of oxidised particles or intermediates on the anode surface.…”

Section: Agreement Of Spectroscopic Results With Thermodynamic Predicmentioning

confidence: 99%

“…Different studies have proposed and supported experimentally the idea that the release of sulphur from SOFC electrode might take place through the oxidation of sulphur [10,18,22,23,29], which premises the presence of oxidised particles or intermediates at the anode surface. But, up to now, spectroscopic measurements with X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), or, Raman microspectroscopy either obtain information from SOFC anode surface in the presence of H 2 S, H 2 , and, possibly even heat, or ex-situ and under postmortem conditions [14,15,22,33].…”

Section: Motivation and Goalmentioning

confidence: 99%

Redox dynamics of sulphur with Ni/GDC anode during SOFC operation at mid- and low-range temperatures: An operando S K-edge XANES study

Nurk

Huthwelker

Braun

et al. 2013

Journal of Power Sources

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h i g h l i g h t s g r a p h i c a l a b s t r a c tAn operando SOFC anode S-poisoning XAS experiment at 550 C to 250 C was performed. S K-edge XANES spectral information at Ni/GDC outer surface was collected.Intermediates with different sulphur oxidation states (6þ, 4þ, 0, 2À) were observed. Proportion of oxidation states changed as a function of temperature. Differences between TD calculations and XAS information were observed and discussed. a r t i c l e i n f o a b s t r a c t Sulphur poisoning of nickelebased solid oxide fuel cell (SOFC) anode catalysts is a well-documented shortcoming, but not yet fully understood. Here, a novel experiment is demonstrated to obtain spectroscopic information at operando conditions, in particular the molecular structure of sulphur species in the sulphur K-shell X-ray absorption near edge structure (XANES) region for a SOFC anode under realistic operando conditions, thus, with the flux of O 2À from cathode to anode. Cooling from T ¼ 550 C stepwise down to 250 C, 5 ppm H 2 S/H 2 reacting with Ni-gadolinium doped ceria (GDC) anode resulted in several sulphur species in different oxidation states (6þ, 4þ, 0, À2) and in amounts being at a minimum at high temperature. According to sulphur speciation analysis, the species could either relate to eSO 4 2À or SO 3 (g), eSO 3 2À or SO 2 (g), S 2 (g) or surface-adsorbed S atoms, and, Ni or Ce sulphides, respectively. The coexistence of different sulphur oxidation states as a function of temperature was analysed in the context of thermodynamic equilibrium calculations. Deviations between experimental results and calculations are most likely due to limitations in the speed of some intermediate oxidation steps as well as due to differences between stoichiometric CeO 2 used in calculations and partially reduced Ce 0.9 Gd 0.1 O 2Àd .

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“…This poisoning effect of H 2 S is usually attributed to the adsorption of sulfur on nickel which blocks active sites for the adsorption of fuel molecules. And although the adsorption of sulfur is reversible and cell performances can recover over the short term, extended exposure to H 2 S-containing fuels will lead to the non-recoverable degradation of cell performances, which can be correlated with reactions between materials and contaminants [19,[73][74][75][76]. To mitigate the effects of sulfur poisoning, alternative anode materials have been proposed and surface modifications to nickel anodes have been designed [30].…”

Section: Study Of Sulfur Poisoning On Nickel Surfacesmentioning

confidence: 99%

In Situ and Surface-Enhanced Raman Spectroscopy Study of Electrode Materials in Solid Oxide Fuel Cells

Blinn

Chen

et al. 2018

Electrochem. Energ. Rev.

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Solid oxide fuel cells (SOFCs) represent next-generation energy sources with high energy conversion efficiencies, low pollutant emissions, good flexibility with a wide variety of fuels, and excellent modularity suitable for distributed power generation. As an electrochemical energy conversion device, the SOFC's performance and reliability depend sensitively on the catalytic activity and stability of electrode materials. To date, however, the development of electrode materials and microstructures is still based largely on trial-and-error methods because of the inadequate understanding of electrode process mechanisms. Therefore, the identification of key descriptors/properties for electrode materials or functional heterogeneous interfaces, especially under in situ/operando conditions, may provide guidance for the design of optimal electrode materials and microstructures. Here, Raman spectroscopy is ideally suited for the probing and mapping of chemical species present on electrode surfaces under operating conditions. And to boost the sensitivity toward electrode surface species, the surfaceenhanced Raman spectroscopy (SERS) technique can be employed, in which thermally robust SERS probes (e.g., Ag@ SiO 2 core-shell nanoparticles) are designed to make in situ/operando analysis possible. This review summarizes recent progresses in the investigation of SOFC electrode materials through Raman spectroscopic techniques, including topics of early stage carbon deposition (coking), coking-resistant anode modification, sulfur poisoning, and cathode degradation. In addition, future perspectives for utilizing the in situ/operando SERS for investigations of other electrochemical surfaces and interfaces are also discussed.

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The effect of current density on H2S-poisoning of nickel-based solid oxide fuel cell anodes

Cited by 96 publications

References 17 publications

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

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

Redox dynamics of sulphur with Ni/GDC anode during SOFC operation at mid- and low-range temperatures: An operando S K-edge XANES study

In Situ and Surface-Enhanced Raman Spectroscopy Study of Electrode Materials in Solid Oxide Fuel Cells

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