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Buzi F, Kreka K, Santiso J, Rapenne L, Sha Z, Douglas JO, Chiabrera F, Morata A, Burriel M, Skinner S, Bernadet L, Baiutti F, Tarancón A. A Self-Assembled Multiphasic Thin Film as an Oxygen Electrode for Enhanced Durability in Reversible Solid Oxide Cells. ACS APPLIED MATERIALS & INTERFACES 2024; 16:43462-43473. [PMID: 39109991 DOI: 10.1021/acsami.4c06290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/23/2024]
Abstract
The implementation of nanocomposite materials as electrode layers represents a potential turning point for next-generation of solid oxide cells in order to reduce the use of critical raw materials. However, the substitution of bulk electrode materials by thin films is still under debate especially due to the uncertainty about their performance and stability under operando conditions, which restricts their use in real applications. In this work, we propose a multiphase nanocomposite characterized by a highly disordered microstructure and high cationic intermixing as a result from thin-film self-assembly of a perovskite-based mixed ionic-electronic conductor (lanthanum strontium cobaltite) and a fluorite-based pure ionic conductor (samarium-doped ceria) as an oxygen electrode for reversible solid oxide cells. Electrochemical characterization shows remarkable oxygen reduction reaction (fuel cell mode) and oxygen evolution activity (electrolysis mode) in comparison with state-of-the-art bulk electrodes, combined with outstanding long-term stability at operational temperatures of 700 °C. The disordered nanostructure was implemented as a standalone oxygen electrode on commercial anode-supported cells, resulting in high electrical output in fuel cell and electrolysis mode for active layer thicknesses of only 200 nm (>95% decrease in critical raw materials with respect to conventional cathodes). The cell was operated for over 300 h in fuel cell mode displaying excellent stability. Our findings unlock the hidden potential of advanced thin-film technologies for obtaining high-performance disordered electrodes based on nanocomposite self-assembly combining long durability and minimized use of critical raw materials.
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Affiliation(s)
- Fjorelo Buzi
- Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Barcelona 08930, Spain
| | - Kosova Kreka
- Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Barcelona 08930, Spain
| | - Jose Santiso
- Catalonia Institute for Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus de la Universitat Autònoma de Barcelona (UAB), Barcelona, Bellaterra 08193, Spain
| | - Laetitia Rapenne
- Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, Grenoble 38000, France
| | - Zijie Sha
- Department of Materials, Imperial College London, Exhibition Road, London SW7, U.K
| | - James O Douglas
- Department of Materials, Imperial College London, Exhibition Road, London SW7, U.K
| | - Francesco Chiabrera
- Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Barcelona 08930, Spain
| | - Alex Morata
- Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Barcelona 08930, Spain
| | - Monica Burriel
- Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, Grenoble 38000, France
| | - Stephen Skinner
- Department of Materials, Imperial College London, Exhibition Road, London SW7, U.K
| | - Lucile Bernadet
- Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Barcelona 08930, Spain
| | - Federico Baiutti
- Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Barcelona 08930, Spain
- Department of Materials Chemistry, National Institute of Chemistry, Hajdrihova 19, Ljubljana SI-1000, Slovenia
| | - Albert Tarancón
- Department of Advanced Materials for Energy, Catalonia Institute for Energy Research (IREC), Barcelona 08930, Spain
- Catalan Institution for Research and Advanced Studies (ICREA), Passeig LlRuís Companys 23, Barcelona 08010, Spain
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2
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Torrigino F, Grimm F, Karl J, Herkendell K. In-situ electrochemical impedance analysis of a commercial SOFC stack fueled by real wood gas. Heliyon 2024; 10:e32509. [PMID: 38952384 PMCID: PMC11215268 DOI: 10.1016/j.heliyon.2024.e32509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Revised: 05/27/2024] [Accepted: 06/05/2024] [Indexed: 07/03/2024] Open
Abstract
The combination of solid oxide fuel cells (SOFCs) and wood gasification has the potential to significantly increase renewable electricity production and decrease emissions. Depending on the quality of the wood gas, degradation processes have a significant impact on the reliability and lifetime of the SOFC. Using electrochemical impedance spectroscopy (EIS) and subsequent distribution of relaxation times (DRT) analysis, the impact on the degradation of coupling wood gasification with a commercial SOFC stack is determined in this study. The thermal behavior of the SOFC stack under various operating conditions, as well as various synthetic wood gas mixtures classified by their hydrogen-to-carbon (H/C) ratio, was assessed. The decrease in the H/C ratio from 8 to 1, observed during syngas and real wood gas operation, leads to a rightward shift in the Nyquist plots, suggesting an increase in the SOFC stack's impedance. Correlations between variations in the H/C ratio and their effects on anodic electrooxidation, ionic conduction, gas transport, and diffusion were identified using DRT analysis to interpret the EIS results. By incorporating an upstream desulfurization system and ensuring an H/C ratio greater than 2, the coupling of biomass gasification with the SOFC stack was stable to degradation issues.
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Affiliation(s)
- Federica Torrigino
- Institute of Energy Process Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fürther Str. 244f, 90429, Nuremberg, Germany
| | - Fabian Grimm
- Institute of Energy Process Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fürther Str. 244f, 90429, Nuremberg, Germany
| | - Jürgen Karl
- Institute of Energy Process Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fürther Str. 244f, 90429, Nuremberg, Germany
| | - Katharina Herkendell
- Institute of Energy Process Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fürther Str. 244f, 90429, Nuremberg, Germany
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3
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Bumberger AE, Nenning A, Fleig J. Transmission line revisited - the impedance of mixed ionic and electronic conductors. Phys Chem Chem Phys 2024; 26:15068-15089. [PMID: 38752774 DOI: 10.1039/d4cp00975d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2024]
Abstract
This contribution provides a comprehensive guide for evaluating the one-dimensional impedance response of dense mixed ionic and electronic conductors based on a physically derived transmission line model. While mass and charge transport through the bulk of a mixed conductor is always described by three fundamental parameters (chemical capacitance, ionic conductivity and electronic conductivity), it is the nature of the contact interfaces that largely determines the observed impedance response. Thus, to allow an intuitive adaptation of the transmission line model for any specific measurement situation, the physical meanings of terminal impedance elements at the ionic and electronic rail ends are explicitly discussed. By distinguishing between charge transfer terminals and electrochemical reaction terminals, the range of possible measurement configurations is categorized into symmetrical, SOFC-type and battery-type setups, all of which are explored on the basis of practical examples from the literature. Also, the transformation of an SOFC electrode into a battery electrode and the relevance of side reactions for the impedance of battery electrodes is discussed.
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Affiliation(s)
| | - Andreas Nenning
- Institute of Chemical Technologies and Analytics, TU Wien, Vienna, Austria.
| | - Juergen Fleig
- Institute of Chemical Technologies and Analytics, TU Wien, Vienna, Austria.
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4
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Siebenhofer M, Nenning A, Rameshan C, Blaha P, Fleig J, Kubicek M. Engineering surface dipoles on mixed conducting oxides with ultra-thin oxide decoration layers. Nat Commun 2024; 15:1730. [PMID: 38409206 PMCID: PMC11258326 DOI: 10.1038/s41467-024-45824-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Accepted: 02/01/2024] [Indexed: 02/28/2024] Open
Abstract
Improving materials for energy conversion and storage devices is deeply connected with an optimization of their surfaces and surface modification is a promising strategy on the way to enhance modern energy technologies. This study shows that surface modification with ultra-thin oxide layers allows for a systematic tailoring of the surface dipole and the work function of mixed ionic and electronic conducting oxides, and it introduces the ionic potential of surface cations as a readily accessible descriptor for these effects. The combination of X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) illustrates that basic oxides with a lower ionic potential than the host material induce a positive surface charge and reduce the work function of the host material and vice versa. As a proof of concept that this strategy is widely applicable to tailor surface properties, we examined the effect of ultra-thin decoration layers on the oxygen exchange kinetics of pristine mixed conducting oxide thin films in very clean conditions by means of in-situ impedance spectroscopy during pulsed laser deposition (i-PLD). The study shows that basic decorations with a reduced surface work function lead to a substantial acceleration of the oxygen exchange on the surfaces of diverse materials.
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Affiliation(s)
- Matthäus Siebenhofer
- Institute of Chemical Technologies and Analytics, TU Wien, Vienna, Austria.
- Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Andreas Nenning
- Institute of Chemical Technologies and Analytics, TU Wien, Vienna, Austria
| | | | - Peter Blaha
- Institute of Materials Chemistry, TU Wien, Vienna, Austria
| | - Jürgen Fleig
- Institute of Chemical Technologies and Analytics, TU Wien, Vienna, Austria
| | - Markus Kubicek
- Institute of Chemical Technologies and Analytics, TU Wien, Vienna, Austria.
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5
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Siebenhofer M, Riedl C, Nenning A, Raznjevic S, Fellner F, Artner W, Zhang Z, Rameshan C, Fleig J, Kubicek M. Crystal-Orientation-Dependent Oxygen Exchange Kinetics on Mixed Conducting Thin-Film Surfaces Investigated by In Situ Studies. ACS APPLIED ENERGY MATERIALS 2023; 6:6712-6720. [PMID: 37388294 PMCID: PMC10301866 DOI: 10.1021/acsaem.3c00870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Accepted: 05/25/2023] [Indexed: 07/01/2023]
Abstract
The oxygen exchange kinetics and the surface chemistry of epitaxially grown, dense La0.6Sr0.4CoO3-δ (LSC) thin films in three different orientations, (001), (110), and (111), were investigated by means of in situ impedance spectroscopy during pulsed laser deposition (i-PLD) and near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). i-PLD measurements showed that pristine LSC surfaces exhibit very fast surface exchange kinetics but revealed no significant differences between the specific orientations. However, as soon as the surfaces were in contact with acidic, gaseous impurities, such as S-containing compounds in nominally pure measurement atmospheres, NAP-XPS measurements revealed that the (001) orientation is substantially more susceptible to the formation of sulfate adsorbates and a concomitant performance decrease. This result is further substantiated by a stronger increase of the work function on (001)-oriented LSC surfaces upon sulfate adsorbate formation and by a faster performance degradation of these surfaces in ex situ measurement setups. This phenomenon has potentially gone unnoticed in the discussion of the interplay between the crystal orientation and the oxygen exchange kinetics and might have far-reaching implications for real solid oxide cell electrodes, where porous materials exhibit a wide variety of differently oriented and reconstructed surfaces.
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Affiliation(s)
- Matthäus Siebenhofer
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Vienna 1060, Austria
- Centre
for Electrochemistry and Surface Technology (CEST), Wiener Neustadt 2700, Austria
| | - Christoph Riedl
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Vienna 1060, Austria
| | - Andreas Nenning
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Vienna 1060, Austria
| | - Sergej Raznjevic
- Erich
Schmid Institute of Materials Science, Austrian
Academy of Sciences, Leoben 8700, Austria
| | - Felix Fellner
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Vienna 1060, Austria
| | - Werner Artner
- X-Ray
Center, Vienna University of Technology, Vienna 1060, Austria
| | - Zaoli Zhang
- Erich
Schmid Institute of Materials Science, Austrian
Academy of Sciences, Leoben 8700, Austria
| | - Christoph Rameshan
- Chair
of Physical Chemistry, Montanuniversität
Leoben, Leoben 8700, Austria
| | - Jürgen Fleig
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Vienna 1060, Austria
| | - Markus Kubicek
- Institute
of Chemical Technologies and Analytics, Vienna University of Technology, Vienna 1060, Austria
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6
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Siebenhofer M, Riedl C, Nenning A, Artner W, Rameshan C, Opitz AK, Fleig J, Kubicek M. Improving and degrading the oxygen exchange kinetics of La 0.6Sr 0.4CoO 3-δ by Sr decoration. JOURNAL OF MATERIALS CHEMISTRY. A 2023; 11:12827-12836. [PMID: 37346740 PMCID: PMC10281333 DOI: 10.1039/d2ta09362f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 02/11/2023] [Indexed: 06/23/2023]
Abstract
Minimizing the overpotential at the air electrode of solid oxide fuel cells (SOFC) is one of the key challenges regarding a broad applicability of this technology. Next to novel materials and geometry optimization, surface modification is a promising and flexible method to alter the oxygen exchange kinetics at SOFC cathode surfaces. Despite extensive research, the mechanism behind the effect of surface decorations is still under debate. Moreover, for Sr decoration, previous studies yielded conflicting results, reporting either a beneficial or a detrimental impact on the oxygen exchange kinetics. In this contribution, in situ impedance spectroscopy during pulsed laser deposition was used to investigate the effect of Sr containing decorations under different deposition conditions. Depending on deposition temperature and interactions with the gas phase, opposing effects of Sr decoration were found. In combination with near-ambient pressure X-ray photoelectron spectroscopy and non-ambient X-ray diffractometry, it was possible to trace this phenomenon back to different chemical environments of the surface Sr. At high temperatures, Sr is deposited as SrO, which can have a beneficial effect on the oxygen exchange kinetics. At low temperatures, SrCO3 adsorbates are formed from trace amounts of CO2 in the measurement atmosphere, causing a decrease of the oxygen exchange rate. These results are in excellent agreement with the concept of surface acidity as a descriptor for the effect of surface decorations, providing further insight into the oxygen exchange kinetics on SOFC cathode surfaces and its degradation. In addition, this study shows that Sr segregation itself initially does not lead to performance degradation but that segregated SrO readily reacts with acidic compounds, reducing the catalytic capability of mixed conducting oxides.
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Affiliation(s)
- Matthäus Siebenhofer
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
- Centre for Electrochemistry and Surface Technology, CEST Wr. Neustadt Austria
| | - Christoph Riedl
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
| | - Andreas Nenning
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
| | | | | | | | - Jürgen Fleig
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
| | - Markus Kubicek
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
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7
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Siebenhofer M, Nenning A, Wilson GE, Kilner JA, Rameshan C, Kubicek M, Fleig J, Blaha P. Electronic and ionic effects of sulphur and other acidic adsorbates on the surface of an SOFC cathode material. JOURNAL OF MATERIALS CHEMISTRY. A 2023; 11:7213-7226. [PMID: 37007913 PMCID: PMC10044886 DOI: 10.1039/d3ta00978e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 03/03/2023] [Indexed: 06/19/2023]
Abstract
The effects of sulphur adsorbates and other typical solid oxide fuel cell (SOFC) poisons on the electronic and ionic properties of an SrO-terminated (La,Sr)CoO3 (LSC) surface and on its oxygen exchange kinetics have been investigated experimentally with near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), low energy ion scattering (LEIS) and impedance spectroscopy as well as computationally with density functional theory (DFT). The experiment shows that trace amounts of sulphur in measurement atmospheres form SO2- 4 adsorbates and strongly deactivate a pristine LSC surface. They induce a work function increase, indicating a changing surface potential and a surface dipole. DFT calculations reveal that the main participants in these charge transfer processes are not sub-surface transition metals, but surface oxygen atoms. The study further shows that sulphate adsorbates strongly affect oxygen vacancy formation energies in the LSC (sub-)surface, thus affecting defect concentrations and oxygen transport properties. To generalize these results, the investigation was extended to other acidic oxides which are technologically relevant as SOFC cathode poisons, such as CO2 and CrO3. The results unveil a clear correlation of work function changes and redistributed charge with the Smith acidity of the adsorbed oxide and clarify fundamental mechanistic details of atomic surface modifications. The impact of acidic adsorbates on various aspects of the oxygen exchange reaction rate is discussed in detail.
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Affiliation(s)
- Matthäus Siebenhofer
- Centre for Electrochemistry and Surface Technology, CEST Wr. Neustadt Austria
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
| | - Andreas Nenning
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
| | | | | | | | - Markus Kubicek
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
| | - Jürgen Fleig
- Institute of Chemical Technologies and Analytics, TU Wien Vienna Austria
| | - Peter Blaha
- Institute of Materials Chemistry, TU Wien Vienna Austria
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8
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Krammer M, Schmid A, Nenning A, Bumberger AE, Siebenhofer M, Herzig C, Limbeck A, Rameshan C, Kubicek M, Fleig J. Closed-Pore Formation in Oxygen Electrodes for Solid Oxide Electrolysis Cells Investigated by Impedance Spectroscopy. ACS APPLIED MATERIALS & INTERFACES 2023; 15:8076-8092. [PMID: 36729502 PMCID: PMC9940111 DOI: 10.1021/acsami.2c20731] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 01/19/2023] [Indexed: 06/18/2023]
Abstract
Electrochemical impedance spectroscopy was used to investigate the chemical capacitance of La0.6Sr0.4CoO3-δ (LSC) thin-film electrodes under anodic polarization (i.e., in the electrolysis mode). For this purpose, electrodes with different microstructures were prepared via pulsed-laser deposition. Analysis of dense electrodes and electrodes with open porosity revealed decreasing chemical capacitances with increasing anodic overpotentials, as expected from defect chemical considerations. However, extremely high chemical capacitance peaks with values in the range of 104 F/cm3 at overpotentials of >140 mV were obtained after annealing for several hours in synthetic air and/or after applying high anodic bias voltages of >750 mV. From the results of several surface analysis techniques and transmission electron microscopy, it is concluded that closed pores develop upon both of these treatments: (i) During annealing, initially open pores get closed by SrSO4, which forms due to strontium segregation in measurement gases with minute traces of sulfur. (ii) The bias treatment causes mechanical failure and morphological changes including closed pores in the bulk of dense films. Under anodic polarization, high-pressure oxygen accumulates in those closed pores, and this causes the capacitance peak. Model calculations based on a real-gas equation allow us to properly predict the experimentally obtained capacitance increase. We demonstrate that analysis of the chemical capacitance of oxygen electrodes in solid oxide electrolysis cells can thus be used as a nondestructive observation tool to detect and quantify closed porosity with a lower detection limit between 10-4 and 10-3.
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Affiliation(s)
- Martin Krammer
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
| | - Alexander Schmid
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
| | - Andreas Nenning
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
| | - Andreas Ewald Bumberger
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
| | - Matthäus Siebenhofer
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
- Centre
for Electrochemical Surface Technology GmbH, Viktor-Kaplan-Straße 2, 2700Wiener Neustadt, Austria
| | - Christopher Herzig
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
| | - Andreas Limbeck
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
| | - Christoph Rameshan
- Institute
of Material Chemistry, Technische Universität
(TU) Wien, Getreidemarkt
9/165-PC, 1060Vienna, Austria
- Chair
of Physical Chemistry, Montanuniversität
Leoben, Franz-Josef-Straße
18, 8700Leoben, Austria
| | - Markus Kubicek
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
| | - Juergen Fleig
- Institute
of Chemical Technologies and Analytics, Technische Universität (TU) Wien, Getreidemarkt 9/164-EC, 1060Vienna, Austria
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9
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Riedl C, Siebenhofer M, Ražnjević S, Bumberger AE, Zhang Z, Limbeck A, Opitz AK, Kubicek M, Fleig J. In situ electrochemical observation of anisotropic lattice contraction of La 0.6Sr 0.4FeO 3-δ electrodes during pulsed laser deposition. Phys Chem Chem Phys 2022; 25:142-153. [PMID: 36476841 PMCID: PMC9768847 DOI: 10.1039/d2cp04977e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
La0.6Sr0.4FeO3-δ (LSF) electrodes were grown on different electrolyte substrates by pulsed laser deposition (PLD) and their oxygen exchange reaction (OER) resistance was tracked in real-time by in situ PLD impedance spectroscopy (i-PLD) inside the PLD chamber. This enables measurements on pristine surfaces free from any contaminations and the direct observation of thickness dependent properties. As substrates, yttria-stabilized zirconia single crystals (YSZ) were used for polycrystalline LSF growth and La0.95Sr0.05Ga0.95Mg0.05O3-δ (LSGM) single crystals or YSZ single crystals with a 5 nm buffer-layer of Gd0.2Ce0.8O2-δ for epitaxial LSF film growth. While polycrystalline LSF electrodes show a constant OER resistance in a broad thickness range, epitaxially grown LSF electrodes exhibit a continuous and strong increase of the OER resistance with film thickness until ≈60 nm. In addition, the activation energy of the OER resistance increases by 0.23 eV compared to polycrystalline LSF. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) measurements reveal an increasing contraction of the out-of-plane lattice parameter in the epitaxial LSF electrodes over electrode thickness. Defect thermodynamic simulations suggest that the decrease of the LSF unit cell volume is accompanied by a lowering of the oxygen vacancy concentration, explaining both the resistive increase and the increased activation energy.
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Affiliation(s)
- Christoph Riedl
- Institute of Chemical Technologies and Analytics, TU WienViennaAustria
| | - Matthäus Siebenhofer
- Institute of Chemical Technologies and Analytics, TU WienViennaAustria,Centre for Electrochemistry and Surface Technology, CEST, WrNeustadtAustria
| | | | | | - Zaoli Zhang
- Erich Schmid Institute for Materials ScienceLeobenAustria
| | - Andreas Limbeck
- Institute of Chemical Technologies and Analytics, TU WienViennaAustria
| | | | - Markus Kubicek
- Institute of Chemical Technologies and Analytics, TU WienViennaAustria
| | - Jürgen Fleig
- Institute of Chemical Technologies and Analytics, TU WienViennaAustria
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