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

Janardhanan, Vinod M.; Monder, Dayadeep S.

doi:10.1149/2.0611414jes

Cited by 13 publications

(16 citation statements)

References 43 publications

(118 reference statements)

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“…Redistribution subject to ECS terms of use (see 139.80.123. 49 Downloaded on 2015-10-05 to IP fuel gas mixture. However, the equilibrium partial pressure of CO 2 is comparatively low due to the high hydrogen gas phase concentration promoting the reverse water gas shift reaction (r-WGS).…”

Section: Resultsmentioning

confidence: 99%

“…Redistribution subject to ECS terms of use (see 139.80.123. 49 Downloaded on 2015-10-05 to IP concentration of 2 ppm. As the H 2 S concentration is further increased methane conversion at the inlet approaches 0%.…”

Section: Resultsmentioning

confidence: 99%

“…Redistribution subject to ECS terms of use (see 139.80.123. 49 Downloaded on 2015-10-05 to IP approach of adjusting these parameters to assist with representing concentration polarization at high current density.…”

Section: Approach and Modeling Summarymentioning

confidence: 99%

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The Influence of Sulfur Formation on Performance and Reforming Chemistry of SOFC Anodes Operating on Methane Containing Fuel

Riegraf

Yurkiv

Schiller

et al. 2015

J. Electrochem. Soc.

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This paper presents a detailed analysis of the influence of sulfur formation on performance and efficiency of Solid Oxide Fuel Cells (SOFC) operating on methane containing fuels. Our previously developed multi-step reaction mechanism of sulfur formation and oxidation is coupled with a complex heterogeneous mechanism of methane reforming, channel gas-flow, porous-media transport and elementary kinetic charge transfer and is used to describe sulfur-induced degradation and performance drops of Ni/YSZ anodes. Experimental literature data is used to validate the model and to interpret important aspects of cell performance degradation. Comparisons of the model predictions to the experiments illustrate that the developed model, without any modifications, reproduces the observed voltage decrease well and is able to capture the changes in fuel conversion and selectivity for different gas mixtures. It is shown that atomically adsorbed sulfur significantly influences heterogeneous reforming chemistry, causing substantial voltage degradation. At constant current densities, cell voltage decreases in a non-linear way with faster recovery than in H 2 /H 2 O mixtures.The enormous usage of fossil fuels over the last decades has led to a large release of green-house gases negatively impacting the climate change. Thus, there is an increased need to develop alternative energy conversion technologies with a reduced carbon-footprint. In this regard, the Solid Oxide Fuel Cell (SOFC) is a promising alternative technology for future energy supply. Due to a high operating temperature range (800 K-1100 K), SOFCs are capable of utilizing a variety of fuels, such as natural gas, biomass gasification products, or syngas. 1-3 However, most of these fuels contain compounds undesired for SOFC operation. One of such substances is hydrogen sulfide (H 2 S), which causes a drastic decrease of cell performance in a short period of time, particularly when a Ni/YSZ cermet is employed as anode material. Therefore, the major objective of this paper is to explore and interpret the influence of sulfur formation at the nickel surface of SOFC anodes on performance and in particular on methane reforming chemistry.Numerous studies have experimentally investigated the influence of sulfur poisoning on Ni/YSZ anodes operated on H 2 /H 2 O fuel gas mixtures identifying the electrochemical hydrogen oxidation process to be severely hindered under these conditions. 4-10 However, in recent years, a growing number of studies has been dedicated to the investigation of sulfur poisoning of Ni/YSZ SOFC anodes operating on hydrocarbon-containing fuels, such as methane, 11-13 reformates, 14 syn-15,16 and biogas. 1 Regardless of the employed fuel gas mixture, in all experimental studies a rapid power output drop was observed already for H 2 S concentrations in the ppm range accompanied by a large increase in total anode resistance. 11,[13][14][15]17 This drop is generally believed to be the result of the chemisorption of sulfur on the active surface sites resulting in a block...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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The Influence of Sulfur Formation on Performance and Reforming Chemistry of SOFC Anodes Operating on Methane Containing Fuel

Riegraf

Yurkiv

Schiller

et al. 2015

J. Electrochem. Soc.

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“…[52][53][54] Appari et al [54] developed a microkinetic sub-mechanism for H 2 S poisoning on nickel, which is coupled with the Detuschmann mechanism [12,55,56] for methane steam and dry reforming on nickel. They reported a sticking coefficient for H 2 S of 0.6, which is similar to the value reported by Riegraf et al [57] (γ = 0.5).…”

Section: Discussionmentioning

confidence: 99%

A comparison of H2S, SO2, and COS poisoning on Ni/YSZ and Ni/K2O-CaAl2O4 during methane steam and dry reforming

Jablonski

Villano

Dean

2015

Applied Catalysis A: General

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Research Highlights: The impact of sulfur poisoning by H 2 S, SO 2 , and COS on methane steam and dry reforming over Ni/YSZ and Ni/K 2 O-CaAl 2 O 4 was measured. Ni/YSZ has 15 times lower active nickel surface area than Ni/K 2 O-CaAl 2 O 4 as measured by hydrogen uptake. Ni/YSZ is essentially completely deactivated while Ni/K 2 O-CaAl 2 O 4 maintains some activity for the same time on stream. For both catalysts, the deactivation rates by H 2 S and SO 2 are comparable, while that for COS is much higher. These results suggest the fuel stream for a solid oxide fuel cell must be cleaned to subppm sulfur levels if Ni/YSZ is the anode material and internal methane reforming is desired. Abstract A systematic comparison of sulfur poisoning on Ni/YSZ and Ni/K 2 O−CaAl 2 O 4 , a commercially available reforming catalyst, demonstrated the heightened and rapid degradation of Ni/YSZ methane reforming activity. Ni/K 2 O−CaAl 2 O 4 has nearly 15 times the hydrogen uptake capacity of Ni/YSZ which implies a difference in active nickel area. Because of this difference in active nickel surface area, Ni/K 2 O−CaAl 2 O 4 was diluted in pure α-Al 2 O 3 to achieve the same active nickel surface area as Ni/YSZ. The turnover frequencies (TOF) for steam methane reforming without sulfur on Ni/YSZ and Ni/K 2 O−CaAl 2 O 4 were similar, although there was some deactivation on Ni/K 2 O−CaAl 2 O 4 possibly as a result of coking which was observed visually. Sulfur deactivation on both catalysts was examined for H 2 S, SO 2, and COS at concentrations of 1, 3, and 5 ppm. Ni/YSZ deactivated rapidly to an activity close to zero. Ni/K 2 O−CaAl 2 O 4 deactivated quickly in the first 20 minutes, but then reached a non-zero steady state activity. The relative deactivation rates for the sulfur species examined were COS > SO 2 ≥ H 2 S. Reaction temperatures of 650 • C, 750 • C, and 800 • C were evaluated, but temperature did not strongly affect deactivation rates strongly for either catalyst. The overarching result of this study is that Ni/YSZ methane reforming activity is more sensitive to sulfur deactivation than a commercial reforming catalyst. The effect is so strong, that the use of Ni/YSZ with any hydrocarbon fuel may require removal of sulfur to sub-ppm levels.

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“…The species transport equations used in this work are adopted from our previous reports on SOFC modeling [22,[24][25][26]. The species transport equation reads under plug flow assumption as:…”

Section: Species Transportmentioning

confidence: 99%

Internal reforming of biogas in SOFC: a model based investigation

Janardhanan

2015

J Solid State Electrochem

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This paper presents a multiphysics model for the simulation of solid oxide fuel cell operating on biogas without external reforming. The model accounts for multicomponent species transport, heterogeneous reaction kinetics on Ni cermet anode, H 2 electrochemical oxidation, and charge transport in the cermet electrodes and electrolyte. The model uses only three adjustable parameters that are fitted against one set of experimental data and then kept constant throughout the study. The model predicted voltage fluctuations are in excellent agreement with experimental measurements reported in the literature. The model also reveals that the assumption of H 2 as the only electrochemically active species is probably inadequate to explain the behavior of cells operating directly on biogas. Thermodynamic analysis is further performed to support this claim made based on model predictions. The model results demonstrate that the thickness of electrochemically active layer is independent of fuel composition under fuel rich conditions, however, thins down as the fuel becomes more and more diluted.

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

Cited by 13 publications

References 43 publications

The Influence of Sulfur Formation on Performance and Reforming Chemistry of SOFC Anodes Operating on Methane Containing Fuel

The Influence of Sulfur Formation on Performance and Reforming Chemistry of SOFC Anodes Operating on Methane Containing Fuel

A comparison of H2S, SO2, and COS poisoning on Ni/YSZ and Ni/K2O-CaAl2O4 during methane steam and dry reforming

Internal reforming of biogas in SOFC: a model based investigation

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