Degradation of Metal-Supported Cells with Ni-YSZ or Ni-Ni<sub>3</sub>Sn-YSZ Anodes Operated with Methane-Based Fuels
Bibliographic record
Abstract
The most common solid oxide fuel cell (SOFC) anode material, nickel - yttria stabilized zirconia (YSZ), displays excellent catalytic properties for fuel oxidation and good electronic conductivity. However, nickel-based anodes can cause carbon deposition when hydrocarbon fuels are used [1]. Nickel catalyzes the formation of carbon filaments in the presence of hydrocarbons under reducing conditions, resulting in coverage of the active sites of the anode, and potentially also to dissolution, precipitation, and metal dusting [2]. It is possible to avoid carbon deposition if sufficient steam is present such that the rate of carbon removal is comparable to or faster than the rate of carbon deposition. However, there is a corresponding decrease in electrical efficiency associated with dilution of the fuel. Metals with electronic structures similar to that of carbon may form an alloy with nickel at the surface, thus reducing carbide formation, and as a consequence, coking [3]. Tin, for example, has been reported to reduce carbon deposition on a Ni-YSZ cermet when present in low amounts such as 1 wt.% of tin with respect to nickel [4,5]. However, volatilization of a metallic tin phase at SOFC operating temperatures may present a problem for long term operation. To increase the stability of tin-containing anodes, we fabricated Ni-Ni3Sn-YSZ anodes using a hybrid solution-precursor / suspension plasma spray (SPPS-SPS) process and compared them to nickel-YSZ anodes made using the same process parameters. Thermogravimetric analyses in a 4% CH4 (balance nitrogen) atmosphere showed that the presence of tin in the anode reduced the rate of carbon deposition. Furthermore, higher amounts of tin resulted in less coking. Ni-Ni3Sn-YSZ and Ni-YSZ anodes were incorporated into metal-supported SOFCs that consisted of a porous metal support (Sandvik Sanergy), samaria-doped ceria (SDC) barrier layer, anode as previously described, YSZ electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3-δ-SDC cathode. Cells were tested at 750°C with air as the oxidant and fuel consisting of 65% CH4, 32% H2, and 3% H2O. The cells were held at a current density of 0.15 A·cm-2 for 500 hours. The cell without tin in the anode began to degrade after approximately 200 hours and catastrophically failed at approximately 425 hours. After testing, we observed that the anode had disintegrated, and as a result, the electrolyte and cathode were completely detached from the metal support. On the other hand, the cell with an anode containing tin did not catastrophically fail, and the cell remained intact after 500 hours of operation. Over 500 hours, the cell potential degraded from 0.841 V to 0.743 V, and scanning electron micrographs showed that the anode had delaminated from the electrolyte in some areas. Nonetheless, the cell with the Ni-Ni3Sn-YSZ anode degraded significantly less than the cell containing a Ni-YSZ anode, suggesting that the addition of Ni3Sn to an anode could be a useful strategy for improving durability of SOFC anodes using hydrocarbon fuels. References 1. S. P. Jiang and S. H. Chan, J. Mater. Science, 39, 4405 (2004). 2. A. Atkinson, S. Barnett, R.J. Gorte, J.T.S Irvine, A.J. McEvoy, M. Mogensen, S.C. Singhal and J. Vohs, Nature Materials, 3, 17 (2004). 3. D.L. Trimm, Catal. Today, 49, 3 (1999). 4. Y. Shiratori, Y. Teroka and K.Sasaki, Solid State Ionics, 177, 1371 (2006). 5. K. Tomishige, Y. Chen and K. Fujimoto, J. Catalysis, 181, 91 (1999).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".