SOFC – A playground for solid state chemistry

Backhaus‐Ricoult, M.

doi:10.1016/j.solidstatesciences.2007.11.021

Cited by 80 publications

(52 citation statements)

References 32 publications

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“…The two temperature ranges for the water exchange with LSM are consistent with the change of stability of valance states of manganese, [49][50][51][52][53][54] and at these temperature ranges, Mn in the B site of ABO 3 shows the ability to actively change valence states. The contour plot of water exchange with LSCF as a function of PO 2 and temperature are shown in Figure 10.…”

Section: Resultssupporting

confidence: 54%

Fundamental Impact of Humidity on SOFC Cathode ORR

Huang

Pellegrinelli

Wachsman

2015

J. Electrochem. Soc.

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Although solid oxide fuel cells (SOFC) have demonstrated excellent performance, the durability of SOFCs under real working conditions is still an issue for commercial deployment. In particular cathode exposure to atmospheric air contaminants, such as humidity, can result in long-term performance degradation issues. Therefore, a fundamental understanding of the interaction between water molecules and cathodes is essential to resolve this issue and further enhance cathode durability. To study the effects of humidity on the oxygen reduction reaction (ORR), we used in-situ 18 O isotope exchange techniques to probe the exchange of water with two of the most common SOFC cathode materials, (La 0.8 Sr 0.2 ) 0.95 MnO 3±δ (LSM) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF). In this experiment, heavy water, D 2 O (with a mass/charge ratio of m/z = 20), is used to avoid the overlapping of H 2 O and the 18 O 2 cracking fraction, which both provide a peak at m/z = 18. A series of temperature programmed isotope exchange measurements were performed to comprehensively study the interaction of water with the cathode surface as a function of temperature, oxygen partial pressure, and water vapor concentration. The results suggest that water and O 2 share the same surface exchange sites, leading to competitive adsorption. Our findings show that water prefers to exchange with LSCF at lower temperatures, around 300-450 • C. For LSM, O 2 is more favorable than water to be adsorbed on the surface and the presence of O 2 limits water exchange. The experimental data are summarized in a Temperature-PO 2 diagram to help visualize how the exchange of water on each material depends on the operating conditions. © The Author Solid oxide fuel cells (SOFC) electrochemically oxidize fuels for the generation of electricity. Two key advantages of SOFCs are their high efficiency and ability to utilize conventional fuels. This fuel flexibility stems from the dissociation and transport of oxygen from the cathode through the electrolyte to the anode, where the fuels are oxidized. Unfortunately, cathode degradation under real working conditions is a factor that limits SOFC performance. 1-6The long term durability of these materials is a major challenge, due to the high temperature required for the thermally activated oxygen reduction reaction (ORR), 7 as well as the variety of gases present during operation. 8,9 The impurities present in air on the cathode side of the cell can induce undesirable reactions. Some of these impurities, such as Cr or silica, 10-15 arise due to the interconnect and seal materials while some are intrinsic to ambient air, such as humidity and CO 2 . 16 Humidity has been found to degrade the performance of (La 0.8 Sr 0.2 ) 0.95 MnO 3±δ (LSM) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) based cells. 11,[17][18][19][20][21][22][23][24] This degradation can be either reversible or irreversible. 21 However, there is no conclusive evidence showing, fundamentally, how water participates in the degradation process, and it is hard to quan...

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Section: Resultssupporting

confidence: 54%

Fundamental Impact of Humidity on SOFC Cathode ORR

Huang

Pellegrinelli

Wachsman

2015

J. Electrochem. Soc.

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“…From a more fundamental point of view it also changes the reaction mechanism from relying on a triple phase boundary (TPB) reaction site to a reaction zone for MIEC electrodes (33)(34)(35). The first MIEC based oxygen electrodes applied for SOEC at DTU Energy were based on LSCF/CGO (lanthanum-strontium-iron-cobaltite/gadoliniumdoped-ceria) electrodes and the achieved long-term stability improvement was reported by Hjalmarsson et al (36).…”

Section: Improved Oxygen Electrodesmentioning

confidence: 99%

A Decade of Solid Oxide Electrolysis Improvements at DTU Energy

et al. 2017

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Solid oxide electrolysis cells (SOECs) can efficiently convert electrical energy (e.g. surplus wind power) to energy stored in fuels such as hydrogen or other synthetic fuels. Performance and durability of the SOEC has increased orders of magnitudes within the last decade. This paper presents a short review of the R&D work on SOEC single cells conducted at DTU Energy from 2005 to 2015. The SOEC improvements have involved increasing the of the oxygen electrode performance, elimination of impurities in the feed streams, optimization of processing routes, and fuel electrode structure optimization. All together, these improvements have led to a decrease in long-term degradation rate from 40 %/kh to 0.4 %/kh for steam electrolysis at -1 A/cm 2 , while the initial area specific resistance has been decreased from 0.44 cm 2 to 0.15 cm 2 at -0.5 A/cm 2 and 750 C.

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“…In the case of interconnects protective layers -either applied as a thin coating or developed in-situ through high-temperature scale formation -are used as a countermeasure but cannot completely suppress the emission of Cr-species into the gas phase [3,4]. Similar degradation issues may be caused by poisoning of the cathode with silicon species released into the gas stream from silicate-based glass sealing materials or heat-resistant alloys used in BOP-components [5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

et al. 2015

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Long-term degradation effects of combined Cr-and Si-poisoning on the promising IT-SOFC cathode materials La 0.6 Sr 0.4 CoO 3-δ and La 2 NiO 4+δ were investigated at 700°C in dry and humid atmospheres for subsequent periods of 1000 hours using dcconductivity relaxation measurements. Degradation-induced changes in chemical composition and morphology of the contaminated sample surfaces were studied by atomic force microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy with energy and wavelength dispersive X-ray analysis. Upon exposure to humid, Cr-and Si-containing gas flows both materials exhibit a strong decrease of the chemical surface exchange coefficient of oxygen by a factor 110 and 40 for La 0.6 Sr 0.4 CoO 3-δ and La 2 NiO 4+δ , respectively, which can be attributed to the formation of Cr-containing crystallites on the degraded sample surfaces. Post-test analyses confirm large amounts of Cr accompanied by a Sr-enrichment within the first 600 nm of the surface of La 0.6 Sr 0.4 CoO 3-δ , indicating the decomposition of the perovskite phase by SrCrO 4 -formation. For La 2 NiO 4+δ the penetration depth of chromium is significantly less and Cr-traces up to a depth of up to 140 nm were determined by depth profiling. For both compounds silicon was found to spread in small patches across the entire sample surface as determined by elemental mapping analysis.

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SOFC – A playground for solid state chemistry

Cited by 80 publications

References 32 publications

Fundamental Impact of Humidity on SOFC Cathode ORR

Fundamental Impact of Humidity on SOFC Cathode ORR

A Decade of Solid Oxide Electrolysis Improvements at DTU Energy

Long-term stability of the IT-SOFC cathode materials La0.6Sr0.4CoO3−δ and La2NiO4+δ against combined chromium and silicon poisoning

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