Voltage and partial pressure dependent defect chemistry in (La,Sr)FeO<sub>3−δ</sub> thin films investigated by chemical capacitance measurements

Schmid, Alexander; Rupp, Ghislain M.; Fleig, Jürgen

doi:10.1039/c7cp07845e

Cited by 46 publications

(110 citation statements)

References 43 publications

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“…The main advantage of this analysis relies on the fact that the defect concentrations can be tuned independently by either oxygen partial pressure or overpotential. More specifically, the defect concentrations are determined by the chemical potential of oxygen in the electrode μ O , which depends on the experimental parameters p O 2 and η according to 23,67 Here the oxygen chemical potential is referenced to 1 bar oxygen (μ O = 0 for 1 bar and η = 0 V). Hence, a certain defect chemical state can be established by different combinations of oxygen partial pressure and overpotential.…”

Section: Data Analysis and Discussionmentioning

confidence: 99%

How To Get Mechanistic Information from Partial Pressure-Dependent Current–Voltage Measurements of Oxygen Exchange on Mixed Conducting Electrodes

2018

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The oxygen incorporation and evolution reaction on mixed conducting electrodes of solid oxide fuel or electrolysis cells involves gas molecules as well as ionic and electronic point defects in the electrode. The defect concentrations depend on the gas phase and can be modified by the overpotential. These interrelationships make a mechanistic analysis of partial pressure-dependent current–voltage experiments challenging. In this contribution it is described how to exploit this complex situation to unravel the kinetic roles of surface adsorbates and electrode point defects. Essential is a counterbalancing of oxygen partial pressure and dc electrode polarization such that the point defect concentrations in the electrode remain constant despite varying the oxygen partial pressure. It is exemplarily shown for La0.6Sr0.4FeO3−δ (LSF) thin film electrodes on yttria-stabilized zirconia how mechanistically relevant reaction orders can be obtained from current–voltage curves, measured in a three-electrode setup. This analysis strongly suggests electron holes as the limiting defect species for the oxygen evolution on LSF and reveals the dependence of the oxygen incorporation rate on the oxygen vacancy concentration. A virtual independence of the reaction rate from the oxygen partial pressure was empirically found for moderate oxygen pressures. This effect, however, arises from a counterbalancing of defect and adsorbate concentration changes.

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Section: Data Analysis and Discussionmentioning

confidence: 99%

How To Get Mechanistic Information from Partial Pressure-Dependent Current–Voltage Measurements of Oxygen Exchange on Mixed Conducting Electrodes

2018

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“…This current is proportional to the change of the overpotential with time, which is characteristic for a capacitive current. Hence, we can introduce the chemical capacitance, which is a measure for how much the oxygen anion concentration in the GDC phase depends on the overpotential, and can be expressed by [46][47][48]…”

Section: Electronion Conduction and Electrochemical Reactions In A Pomentioning

confidence: 99%

“…Therefore, the expected chemical capacitance can be reliably predicted from literature data, as shown in Figure 10a. Moreover, for low-point defect concentrations where defect interactions are weak, the capacitance value can serve as a fingerprint for the concentration of oxygen vacancies and electronic defects [46][47][48]64], and reported values are largely reproduced within the literature.…”

Section: Chemical Capacitancementioning

confidence: 99%

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

et al. 2020

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Detailed insight into electrochemical reaction mechanisms and rate limiting steps is crucial for targeted optimization of solid oxide fuel cell (SOFC) electrodes, especially for new materials and processing techniques, such as Ni/Gd-doped ceria (GDC) cermet anodes in metal-supported cells. Here, we present a comprehensive model that describes the impedance of porous cermet electrodes according to a transmission line circuit. We exemplify the validity of the model on electrolyte-supported symmetrical model cells with two equal Ni/Ce0.9Gd0.1O1.95-δ anodes. These anodes exhibit a remarkably low polarization resistance of less than 0.1 Ωcm2 at 750 °C and OCV, and metal-supported cells with equally prepared anodes achieve excellent power density of >2 W/cm2 at 700 °C. With the transmission line impedance model, it is possible to separate and quantify the individual contributions to the polarization resistance, such as oxygen ion transport across the YSZ-GDC interface, ionic conductivity within the porous anode, oxygen exchange at the GDC surface and gas phase diffusion. Furthermore, we show that the fitted parameters consistently scale with variation of electrode geometry, temperature and atmosphere. Since the fitted parameters are representative for materials properties, we can also relate our results to model studies on the ion conductivity, oxygen stoichiometry and surface catalytic properties of Gd-doped ceria and obtain very good quantitative agreement. With this detailed insight into reaction mechanisms, we can explain the excellent performance of the anode as a combination of materials properties of GDC and the unusual microstructure that is a consequence of the reductive sintering procedure, which is required for anodes in metal-supported cells.

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“…Also temperature and p(O 2 ) dependent defect concentrations may cause a change for one and the same mechanism. 33 The complete evolution of the surface exchange resistance over the course of the experiments is visualized in Fig. 12.…”

Section: Comparison Of Oxygen Exchange Properties Measured In Situ (Pmentioning

confidence: 99%

“…For further discussion we may relate the chemical capacitance to the defect chemistry of the material. The capacitance of a lm with diluted defects can be interpreted with regard to the chemical composition according to: 33,39…”

Section: Chemical Capacitances Measured In Situ and Ex Situmentioning

confidence: 99%

Oxygen exchange kinetics and nonstoichiometry of pristine La_0.6Sr_0.4CoO_3−δ thin films unaltered by degradation

et al. 2020

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Voltage and partial pressure dependent defect chemistry in (La,Sr)FeO_3−δ thin films investigated by chemical capacitance measurements

Abstract: Chemical capacitance measurements are used to study the defect chemistry of La0.6Sr0.4FeO3–δ thin films and their polarization (η) and pO2 dependence. Important point defects are oxygen vacancies (), electrons (e′) and holes (h˙).

Cited by 46 publications

References 43 publications

How To Get Mechanistic Information from Partial Pressure-Dependent Current–Voltage Measurements of Oxygen Exchange on Mixed Conducting Electrodes

How To Get Mechanistic Information from Partial Pressure-Dependent Current–Voltage Measurements of Oxygen Exchange on Mixed Conducting Electrodes

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

Oxygen exchange kinetics and nonstoichiometry of pristine La_0.6Sr_0.4CoO_3−δ thin films unaltered by degradation

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Voltage and partial pressure dependent defect chemistry in (La,Sr)FeO3−δ thin films investigated by chemical capacitance measurements

Abstract: Chemical capacitance measurements are used to study the defect chemistry of La0.6Sr0.4FeO3–δ thin films and their polarization (η) and pO2 dependence. Important point defects are oxygen vacancies (), electrons (e′) and holes (h˙).

Cited by 46 publications

References 43 publications

How To Get Mechanistic Information from Partial Pressure-Dependent Current–Voltage Measurements of Oxygen Exchange on Mixed Conducting Electrodes

How To Get Mechanistic Information from Partial Pressure-Dependent Current–Voltage Measurements of Oxygen Exchange on Mixed Conducting Electrodes

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

Oxygen exchange kinetics and nonstoichiometry of pristine La0.6Sr0.4CoO3−δ thin films unaltered by degradation

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Product

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Voltage and partial pressure dependent defect chemistry in (La,Sr)FeO_3−δ thin films investigated by chemical capacitance measurements

Oxygen exchange kinetics and nonstoichiometry of pristine La_0.6Sr_0.4CoO_3−δ thin films unaltered by degradation