From Ni-YSZ to sulfur-tolerant anode materials for SOFCs: electrochemical behavior, in situ characterization, modeling, and future perspectives

Cheng, Zhe; Wang, Jeng Han; Choi, YongMan; Yang, Lei; Lin, Ming‐Chang; Liu, Meilin

doi:10.1039/c1ee01758f

Cited by 306 publications

(260 citation statements)

References 190 publications

(330 reference statements)

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“…However, it presents some drawbacks including those associated with thermal cycling, redox stability due to the significant volume changes upon oxidation of Ni to NiO and thus affecting the mechanical integrity of the cell, as well as sulphur deposition or coking when 3 carbon rich fuel streams are used [5,6]. In recent years, several efforts are being performed in order to elucidate the redox-cycling problem [7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

The influence of the reducing conditions on the final microstructure and performance of nickel-yttria stabilized zirconia cermets

Monzón

Laguna‐Bercero

2016

Electrochimica Acta

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Ni-YSZ (yttria stabilized zirconia) cermets are the most widespread composite materials to be used as SOFC fuel electrodes. These materials are generally fabricated by the reduction of NiO to Ni in a NiO-YSZ composite, where the reducing conditions have a great effect in the final microstructure of the electrode. In the present work, several reducing conditions were explored in order to find the most suitable microstructure for anode-supported microtubular solid oxide fuel cells (SOFCs). Samples were firstly reduced in either pure or diluted H2 (dry or humidified), at temperatures ranging from 400 to 800 °C while their DC conductivity was monitored. The highest conductivity value was measured for the sample reduced in pure humidified hydrogen at 800°C. However, this sample experienced conductivity degradation in comparison with samples reduced under dry conditions. For the studied temperature range, nucleation of nano-porous nickel particles is firstly formed during reduction. However, from our experiments it was concluded that those nanoparticles are not stable with time, at least at temperatures between 600 ºC and 800 ºC. Electrochemical characterization of complete microtubular cells under real wet conditions was also performed under current load, confirming that the microstructure of the Ni-YSZ cermet is still evolving during operation.

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Section: Introductionmentioning

confidence: 99%

The influence of the reducing conditions on the final microstructure and performance of nickel-yttria stabilized zirconia cermets

Monzón

Laguna‐Bercero

2016

Electrochimica Acta

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“…Hansen and Rostrup-Nielsen, 13 and more recently Cheng et al, 1 wrote excellent reviews on sulfur poisoning of SOFC anodes in which they summarized the current understanding of this process from an experimental perspective considering Ni based anodes as well as other more sulfur-tolerant oxide based anodes. It is generally accepted that the degree of sulfur poisoning is lower at higher temperatures, and lower p H 2 S / p H 2 .…”

mentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

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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“…An activation energy (E a,e ) of 137 kJ/mol for the cathode and 140 kJ/mol for the anode are used by Patcharavorachot et al [20] and Aguiar et al [22] The heat generation by the electrochemical reactions and due to the losses through the activation, the ohmic and the concentration polarizations is given by [25]: (12) Here, i is the current density,  is the ion/electron conductivity, Q h is the heat generation/consumption and S r is the entropy change of the electrochemical reactions, calculated from the data in [37] for the anode and the cathode TPBs, respectively.…”

Section: Ion and Electron Transport As Well As Electrochemical Reactionsmentioning

confidence: 99%

“…An important new direction for SOFC research is to develop a predictive multiscale (from density functional theory (DFT) to continuum) computational framework, through a rigorous validation at each scale by carefully-designed experiments performed under in situ conditions. However, major challenges still remain to bridge the gaps between the models at different scales or between theoretical predictions and experiments [12]. Modeling and simulation across the time and length scales provide unique opportunities to understand properties and phenomena that are inaccessible and difficult to address with experimental effort, or have multifaceted interactions.…”

Section: Introductionmentioning

confidence: 99%

Three dimensional modeling of an solid oxide fuel cell coupling charge transfer phenomena with transport processes and heat generation

Andersson

Paradis

Yuan

et al. 2013

Electrochimica Acta

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From Ni-YSZ to sulfur-tolerant anode materials for SOFCs: electrochemical behavior, in situ characterization, modeling, and future perspectives

Cited by 306 publications

References 190 publications

The influence of the reducing conditions on the final microstructure and performance of nickel-yttria stabilized zirconia cermets

The influence of the reducing conditions on the final microstructure and performance of nickel-yttria stabilized zirconia cermets

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

Three dimensional modeling of an solid oxide fuel cell coupling charge transfer phenomena with transport processes and heat generation

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