Chemical Stability and CO<sub>2</sub> Electrolysis Performance of La<sub>0.3</sub>Sr<sub>0.7</sub>Fe<sub>0.7</sub>Cr<sub>0.3</sub>O<sub>3-</sub> <sub>δ</sub> in CO<sub>2</sub>/CO Environments
Bibliographic record
Abstract
LMFCr (M = Sr, Ca) has emerged as a highly promising class of perovskite oxide materials for use as symmetrical electrodes in reversible solid oxide fuel cells (RSOFCs).1 While there are numerous studies on the efficacy of these materials as symmetrical electrodes for SOFCs,1-5 a detailed study on their chemical stability and electrochemical performance as fuel electrodes in CO2/CO environments has not yet been reported. This work aims to address the stability of the Sr analogue of LMFCr, namely, La0.3Sr0.7Fe0.7CrO3-δ (LSFCr), in low pO2 environments consisting of CO2/CO gas mixtures (10-11-10-18 atm) to establish the range of pO2 over which the electrode material is structurally and electrochemically stable. This is relevant under CO2 reduction conditions as the stability limit will define the allowable CO2 utilization in these cells in practice. The chemical and phase stability was studied on LSFCr powders and pellets via XRD, TGA, and SEM in different pO2 atmospheres ranging from pure CO2, CO (balance N2), and 90-70% CO2:10-30% CO containing mixtures. Powdered LSFCr remains structurally stable in 20-100% CO2 (balance N2, pO2 = 10-11 – 10-12 atm) from room temperature to 800 oC without any decomposition. On the other extreme, a reversible decomposition occurs at 800 oC in 30% CO (balance N2, pO2 ~ 10-26 atm) resulting in the formation of a Ruddlesden-Popper phase, Fe nanoparticles (NPs), and some carbon fibers, originating from the Fe NPs. However, this decomposition can be reversed by heat treatment in air at 800 oC. While no evidence for coke formation is obtained in 90-70% CO2:10-30% CO (pO2 = 10-17 – 10-18 atm) mixtures at 800 oC, in 70CO2:30CO, minor impurities of SrCO3 and Fe NPs are observed, with the latter potentially being beneficial to the electrochemical activity of the perovskite. Electrochemical characterization was carried out on symmetrical cells prepared by printing ~25 µm single phase LSFCr electrode layers, with an area of ca. 0.5 cm2, on both sides of a 1” diameter SDC buffered YSZ electrolyte, followed by painting on Au paste as the current collectors. The cells were mounted in an open flanges cell testing setup (Fiaxell, Switzerland) and supplied with 50 mL/min air at the oxygen electrode and 50 mL/min CO2:CO mixtures at the fuel electrode. The performance of full cells was determined in various CO2:CO ratios (Pure CO2, 90:10, and 70:30) at 800 oC via electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and chronoamperometry. Consistent with prior work, symmetrical 2-electrode full cells showed very good electrochemical performance at 800 oC, both in the SOFC and SOEC modes. Furthermore, LSFCr full cells exhibited excellent short-term stability in 15-min potentiostatic stability tests at 1.2-1.5 V, while medium-term potentiostatic tests at 1.1 and 1.2 V showed that LSFCr exhibits exceptional stability during CO2 electrolysis in all gas atmospheres over several 100 hours, with the oxygen electrode facilitating the oxygen evolution reaction (OER) at the same time. These results suggest that LSFCr has the potential to be a very efficient and stable electrode material for symmetrical SOC applications. References (1) Chen, M.; Paulson, S.; Thangadurai, V.; Birss, V. Journal of Power Sources 2013, 236, 68-79. (2) Chen, M.; Paulson, S.; Thangadurai, V.; Birss, V. ECS Transactions 2012, 45, 343-348. (3) Chen, M.; Paulson, S.; Kan, W. H.; Thangadurai, V.; Birss, V. Journal of Materials Chemistry A 2015, 3, 22614-22626. (4) Molero-Sanchez, B.; Addo, P.; Buyukaksoy, A.; Paulson, S.; Birss, V. Faraday Discussions 2015, 182, 159-175. (5) Addo, P. K.; Molero-Sanchez, B.; Chen, M.; Paulson, S.; Birss, V. Fuel Cells 2015, 15, 689-696.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".