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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 DOI: 10.1038/s41467-024-45824-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [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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2
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Kumar A, Sanger A, Kang SB, Chandra R. Interface Engineering-Driven Room-Temperature Ultralow Gas Sensors with Elucidating Sensing Performance of Heterostructure Transition Metal Dichalcogenide Thin Films. ACS Sens 2023; 8:3824-3835. [PMID: 37769211 DOI: 10.1021/acssensors.3c01290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/30/2023]
Abstract
In this report, we investigate the room-temperature gas sensing performance of heterostructure transition metal dichalcogenide (MoSe2/MoS2, WS2/MoS2, and WSe2/MoS2) thin films grown over a silicon substrate using a pulse laser deposition technique. The sensing response of the aforementioned sensors to a low concentration range of NO2, NH3, H2, CO, and H2S gases in air has been assessed at room temperature. The obtained results reveal that the heterojunctions of metal dichalcogenide show a drastic change in gas sensing performance compared to the monolayer thin films at room temperature. Nevertheless, the WSe2/MoS2-based sensor was found to have an excellent selectivity toward NO2 gas with a particularly high sensitivity of 10 ppb. The sensing behavior is explained on the basis of a change in electrical resistance as well as carrier localization prospects. Favorably, by developing a heterojunction of diselenide and disulfide nanomaterials, one may find a simple way of improving the sensing capabilities of gas sensors at room temperature.
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Affiliation(s)
- Ashwani Kumar
- Nanoscience Laboratory, Institute Instrumentation Centre, IIT Roorkee, Roorkee 247667, India
- Department of Physics, Graphic Era (Deemed to be University), Dehradun, Uttarakhand 248002, India
| | - Amit Sanger
- Department of Physics, Netaji Subhas University of Technology, Dwarka Sector-3, New Delhi 110078, India
| | - Sung Bum Kang
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Ramesh Chandra
- Nanoscience Laboratory, Institute Instrumentation Centre, IIT Roorkee, Roorkee 247667, India
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3
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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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4
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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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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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6
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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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7
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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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8
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Krammer M, Schmid A, Siebenhofer M, Bumberger AE, Herzig C, Limbeck A, Kubicek M, Fleig J. Formation and Detection of High-Pressure Oxygen in Closed Pores of La 0.6Sr 0.4CoO 3-δ Solid Oxide Electrolysis Anodes. ACS APPLIED ENERGY MATERIALS 2022; 5:8324-8335. [PMID: 35909806 PMCID: PMC9326814 DOI: 10.1021/acsaem.2c00888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
The chemical capacitance of La0.6Sr0.4CoO3-δ (LSC) thin film microelectrodes with different microstructures was investigated upon varying anodic DC voltages. Dense and porous electrodes (open porosity) were prepared by using different parameters during pulsed laser deposition (PLD). Furthermore, electrodes with closed porosity were fabricated by depositing a dense capping layer on a porous film. Electrochemical impedance spectroscopy (EIS) was performed in synthetic air at 460 and 608 °C with anodic DC voltages up to 440 mV. Chemical capacitance values of the electrodes were derived from the obtained spectra. While the chemical capacitance of dense and porous electrodes decreased as expected with increasing anodic overpotential, electrodes with closed pores exhibited very unusual peaks with extremely high values of >8000 F/cm3 at overpotentials of >100 mV. We demonstrate that this huge capacitance increase agrees very well with calculated chemical capacitances deduced from a real gas equation. Hence, we conclude that the formation of highly pressurized oxygen (up to gas pressures of ∼104 bar) in closed pores is responsible for this strong capacitive effect at anodic overpotentials. Such measurements can thus detect and quantify the buildup of high internal gas pressures in closed pores at the anode side of solid oxide electrolysis cells.
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Affiliation(s)
- Martin Krammer
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
| | - Alexander Schmid
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
| | - Matthäus Siebenhofer
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
- Centre
for Electrochemical Surface Technology GmbH, Viktor-Kaplan-Straßze 2, 2700 Wiener Neustadt, Austria
| | - Andreas Ewald Bumberger
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
| | - Christopher Herzig
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
| | - Andreas Limbeck
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
| | - Markus Kubicek
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
| | - Juergen Fleig
- TU
Wien, Institute of Chemical
Technologies and Analytics, Getreidemarkt 9/164-EC, 1060 Vienna, Austria
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Riedl C, Siebenhofer M, Nenning A, Schmid A, Weiss M, Rameshan C, Limbeck A, Kubicek M, Opitz AK, Fleig J. In situ techniques reveal the true capabilities of SOFC cathode materials and their sudden degradation due to omnipresent sulfur trace impurities. JOURNAL OF MATERIALS CHEMISTRY. A 2022; 10:14838-14848. [PMID: 35923869 PMCID: PMC9295724 DOI: 10.1039/d2ta03335f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 06/22/2022] [Indexed: 06/15/2023]
Abstract
In this study, five different mixed conducting cathode materials were grown as dense thin films by pulsed laser deposition (PLD) and characterized via in situ impedance spectroscopy directly after growth inside the PLD chamber (i-PLD). This technique enables quantification of the oxygen reduction kinetics on pristine and contaminant-free mixed conducting surfaces. The measurements reveal excellent catalytic performance of all pristine materials with polarization resistances being up to two orders of magnitude lower than those previously reported in the literature. For instance, on dense La0.6Sr0.4CoO3-δ thin films, an area specific surface resistance of ∼0.2 Ω cm2 at 600 °C in synthetic air was found, while values usually >1 Ω cm2 are measured in conventional ex situ measurement setups. While surfaces after i-PLD measurements were very clean, ambient pressure X-ray photoelectron spectroscopy (AP-XPS) measurements found that all samples measured in other setups were contaminated with sulfate adsorbates. In situ impedance spectroscopy during AP-XPS revealed that already trace amounts of sulfur present in high purity gases accumulate quickly on pristine surfaces and lead to strongly increased surface polarization resistances, even before the formation of a SrSO4 secondary phase. Accordingly, the inherent excellent catalytic properties of this important class of materials were often inaccessible so far. As a proof of concept, the fast kinetics observed on sulfate-free surfaces were also realized in ex situ measurements with a gas purification setup and further reduces the sulfur concentration in the high purity gas.
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Affiliation(s)
- Christoph Riedl
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
| | - Matthäus Siebenhofer
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
- CEST Kompetenzzentrum für Elektrochemische Oberflächentechnologie GmbH, TFZ - Wiener Neustadt Viktor-Kaplan-Strasse 2 2700 Wiener Neustadt Austria
| | - Andreas Nenning
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
| | - Alexander Schmid
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
| | - Maximilian Weiss
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
| | - Christoph Rameshan
- Institute of Materials Chemistry, TU Wien Getreidemarkt 9-E165-PC 1060 Vienna Austria
| | - Andreas Limbeck
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
| | - Markus Kubicek
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
| | - Alexander Karl Opitz
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
| | - Juergen Fleig
- Institute of Chemical Technologies and Analytics, TU Wien Getreidemarkt 9-E164 1060 Vienna Austria
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