Revising the role of chromium on the surface of perovskite electrodes: Poison or promoter for the solid oxide electrolysis cell performance?

Chen, Dingkai; Mewafy, Basma; Paloukis, Fotios; Zhong, Liping; Papaefthimiou, Vasiliki; Dintzer, Thierry; Papazisi, Kalliopi-Maria; Balomenou, Stella; Tsiplakides, D.; Teschner, Detre; Pérez-Dieste, Virgínia; Escudero, Carlos; Zafeiratos, Spyridon

doi:10.1016/j.jcat.2019.11.032

Cited by 11 publications

(14 citation statements)

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“…[57][58][59][60] The existence of Cr in a higher oxidation state, Cr 6+ , on the samples annealed in dry and wet oxygen with high pO 2 , is conrmed by the peak at approximately 580 eV and in good agreement with the binding energies reported for CrO 3 and La 0.8 Sr 0.2 CrO 3 . 38,55,59,60 There is a single peak arising for Cr 6+ due to no unpaired electrons in its outermost shell. On the contrary, the Cr 6+ signal can scarcely be observed on the sample annealed in the water vapour environment with low pO 2 .…”

Section: Propertiesmentioning

confidence: 99%

“…[63][64][65][66][67][68][69] In this case, the SrCrO 4 is likely formed through the oxidation of Cr species on the sample surface to volatile Cr 6+ species such as CrO 3 . 38 The Cr 6+ gaseous species would further react with the segregated SrO particles on the surface to form SrCrO 4 -like oxides: [63][64][65][66] CrO 3(g) + SrO (surf) / SrCrO 4(surf)…”

Section: Propertiesmentioning

confidence: 99%

“…SrCrO 4 ). 38 In addition, the extent of cation segregation has been proven to depend on external conditions such as temperature 11,16,17,24 and oxygen partial pressure. 11,39,40 Although the surface composition evolution of MIEC electrodes is widely studied, there has been little discussion on the effect of operating conditions on a model system.…”

Section: Introductionmentioning

confidence: 99%

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Understanding surface chemical processes in perovskite oxide electrodes

et al. 2023

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Section: Propertiesmentioning

confidence: 99%

Section: Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Understanding surface chemical processes in perovskite oxide electrodes

et al. 2023

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“…This finding is consistent with previously reported spectra measured on La 0.75 Sr 0.25 Cr 0.9 Fe 0.1 O 3 in 3.5 mbar of oxygen at 300 °C, which showed the presence of Cr 4+48 . It deviates from the spectra for Cr 6+ found on La 0.75 Sr 0.25 Cr 0.9 Fe 0.1 O 3 in 0.5 mbar of oxygen at 890 °C . The indication of existing Cr 4+ in the lattice was not surprising and can be correlated to the oxidation of Cr 3+ in oxidizing conditions, as described in eq : 1 2 O 2 ( g ) + V O · · + 2 Cr Cr × ↔ O O × + 2 Cr Cr · where Cr Cr × denotes Cr 3+ on Cr 3+ sites, O O × is a neutral lattice oxygen, and Cr Cr · represents Cr 4+ on Cr 3+ sites.…”

Section: Resultsmentioning

confidence: 99%

Studying Surface Chemistry of Mixed Conducting Perovskite Oxide Electrodes with Synchrotron-Based Soft X-rays

Sha,

Kerherve,

van Spronsen

et al. 2023

J. Phys. Chem. C

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A fundamental understanding of the electrochemical reactions and surface chemistry at the solid−gas interface in situ and operando is critical for electrode materials applied in electrochemical and catalytic applications. Here, the surface reactions and surface composition of a model of mixed ionic and electronic conducting (MIEC) perovskite oxide, (La 0.8 Sr 0.2 ) 0.95 Cr 0.5 Fe 0.5 O 3-δ (LSCrF8255), were investigated in situ using synchrotron-based near-ambient pressure (AP) X-ray photoelectron spectroscopy (XPS) and nearedge X-ray absorption fine-structure spectroscopy (NEXAFS). The measurements were conducted with a surface temperature of 500 °C under 1 mbar of dry oxygen and water vapor, to reflect the implementation of the materials for oxygen reduction/evolution and H 2 O electrolysis in the applications such as solid oxide fuel cell (SOFC) and electrolyzers. Our direct experimental results demonstrate that, rather than the transition metal (TM) cations, the surface lattice oxygen is the significant redox active species under both dry oxygen and water vapor environments. It was proven that the electron holes formed in dry oxygen have a strong oxygen character. Meanwhile, a relatively higher concentration of surface oxygen vacancies was observed on the sample measured in water vapor. We further showed that in water vapor, the adsorption and dissociation of H 2 O onto the perovskite surface were through forming hydroxyl groups. In addition, the concentration of Sr surface species was found to increase over time in dry oxygen due to Sr surface segregation, with the presence of oxygen holes on the surface serving as an additional driving force. Comparatively, less Sr contents were observed on the sample in water vapor, which could be due to the volatility of Sr(OH) 2 . A secondary phase was also observed, which exhibited an enrichment in B-site cations, particularly in Fe and relatively in Cr, and a deficiency in A-site cation, notably in La and relatively in Sr. The findings and methodology of this study allow for the quantification of surface defect chemistry and surface composition evolution, providing crucial understanding and design guidelines in the electrocatalytic activity and durability of electrodes for efficient conversions of energy and fuels.

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“…Under steam electrolysis conditions, La 0.75 Sr 0.25 Cr 0.9 Fe 0.1 O 3− δ oxide is characterised by surface enrichment of Sr 2+ associated with Cr segregation due to oxidation of Cr 3+ cations to Cr 6+ and formation of SrCrO 4 . 179 The presence of SrCrO 4 on the surface favours the electrode performance during electrolysis due to the high activity of this compound. The calcination in humidified oxygen p H 2 O = 30 mbar of (La 0.8 Sr 0.2 ) 0.95 Cr 0.5 Fe 0.5 O 3− δ oxide leads to the suppression of strontium segregation.…”

Section: Characterization Of Surface Segregation: Approachesmentioning

confidence: 99%