Operando Soft X‐ray Absorption Spectroscopic Study on a Solid Oxide Fuel Cell Cathode during Electrochemical Oxygen Reduction

Nakamura, Takashi; Oike, Ryo; Kimura, Yuta; Tamenori, Y.; Kawada, Tatsuya; Amezawa, Koji

doi:10.1002/cssc.201700237

Cited by 20 publications

(15 citation statements)

References 43 publications

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“…Recently, Nakamura et al confirmed the electronic structural changes in the outermost orbital of a La 2 NiO 4+ δ film electrode during electrochemical ORR by operando sXAS ( Figure a–c) . By changing the O 2 atmospheric pressure and applying an electrical potential, an increase/decrease in the pre‐edge peak of the O K‐edge XAS spectrum was observed with cathodic/anodic polarization.…”

Section: Oxygen Reduction Reactionmentioning

confidence: 82%

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In Situ/Operando Characterization Techniques to Probe the Electrochemical Reactions for Energy Conversion

et al. 2018

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electrolyzers. [5] Unfortunately, the overall efficiency and performance of these greenenergy devices have been largely limited by the sluggish kinetics of the ORR and OER processes, which involve a relatively unfavorable four-electron stepwise chargetransfer reaction. [2] Apart from the ORR and OER, the electrocatalytic conversion of emitted carbon dioxide (CO 2 ) to high value chemicals and fuels offers another promising alternative approach to mitigate the most urgent challenge regarding renewable energy production and environmental remediation. [6] Key technologies based on an efficient CO 2 reduction reaction (CO 2 RR) allow us to move away from the reliance on fossil fuels and close the carbon cycle. In addition, the hydrogen evolution reaction (HER) is also critical for clean and renewable energy technology development, as hydrogen can be directly used as the fuel, with water as the only product from the combustion of H 2 . [7] Based on the above information, it can be realized that most of the electrochemical processes for energy conversion are based on catalytic chemical transformations, which take place at the interfaces between solids and liquids or gases. Therefore, facilitating the electrochemical reaction at the interface is essential.Due to lack of valuable information from the real-time observation via in situ experiments, most understandings of the elementary reactions, the geometry of short-lived intermediates, and the thermodynamic energy difference between those elementary steps still rely on quantum chemical calculations, for example, density functional theory (DFT). [8] The ex situ spectroscopic comparison, commonly employing X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy (sXAS) as the surface-sensitive examining tools, [9] between the pre-and post-chemical states of the catalyst in a specific electrochemical reaction is the most common method to deduce the possible active sites. However, the simultaneous presence of contamination and/or undesired surface functional groups on the surface of the catalyst, induced by electrochemical activation or exposure to air during chamber-to-chamber transportation, can disturb the interpretation of the spectroscopic fingerprints of the potential active sites. Besides, an ex situ spectroscopic comparison cannot always guarantee a meaningful trend or relevance between the chemical variation of the catalyst and the electrochemical activity. Therefore, the development of the operando measurement technique is recognized as an effective method for providing information of the electronic structural The water-splitting reaction, including the hydrogen and oxygen evolution reactions, as well as the electrochemical oxygen and CO 2 reduction reactions offer promising solutions to address the global energy scarcity and the associated environmental issues. However, the lack of deep insight into the reaction mechanisms and clear identification of the catalytic active sites hinder any breakthrough for the development of efficient electroca...

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Section: Oxygen Reduction Reactionmentioning

confidence: 82%

Section: Oxygen Reduction Reactionmentioning

confidence: 99%

In Situ/Operando Characterization Techniques to Probe the Electrochemical Reactions for Energy Conversion

et al. 2018

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“…Another exciting study focused on the RDS determination by operando XAS was carried out by Amezawa's group on fuel cells using La2NiO4+δ dense-film electrodes [29]. In this work soft X-rays were used, allowing the measurement of both the O K-edge and the Ni L-edge X-ray absorption spectra at 500 °C, at several oxygen partial pressures and under polarization.…”

Section: Synchrotron Based X-ray Techniquesmentioning

confidence: 99%

In situ and operando characterisation techniques for solid oxide electrochemical cells: recent advances

2020

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Oxygen activity and surface stability are two key parameters in the search for advanced materials for intermediate temperature solid oxide electrochemical cells, as overall device performance depends critically on them. In particular in situ and operando characterisation techniques have accelerated the understanding of degradation processes and the identification of active sites, motivating the design and synthesis of improved, nanoengineered materials. In this short topical review we report on the latest developments of various sophisticated in situ and operando characterization techniques, including transmission and scanning electron microscopy, surface-enhanced Raman spectroscopy, electrochemical impedance spectroscopy, x-ray diffraction and synchrotron-based x-ray photoelectron spectroscopy and x-ray absorption spectroscopy, among others. We focus on their use in three emerging topics, namely: (i) the analysis of general electrochemical reactions and the surface defect chemistry of electrode materials; (ii) the evolution of electrode surfaces achieved by nanoparticle exsolution for enhanced oxygen activity and (iii) the study of surface degradation caused by Sr segregation, leading to reduced durability. For each of these topics we highlight the most remarkable examples recently published. We anticipate that ongoing improvements in the characterisation techniques and especially a complementary use of them by multimodal approaches will lead to improved knowledge of operando processes, hence allowing a significant advancement in cell performance in the near future.

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“…[7][8][9][10] Although some studies successfully observed the physical/chemical states of electrodes and electrolytes, the reaction mechanisms could not be directly clarified because the applied analytical techniques required impractical experimental conditions (e.g., high-vacuum conditions) or provided only limited information. Recently, X-ray diffraction 11 and X-ray absorption techniques 12,13 have been used to analyze cathode reactions in high-temperature and high-voltage applications. When hard X-rays with energy of >5000 eV are used, the measurements do not require any specific experimental conditions, e.g., high vacuum and low temperature; thus, X-ray based techniques are considered to be suitable for in situ analysis of high-temperature electrochemical devices.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Cathodic Reaction Mechanism in Solid Oxide Fuel Cells by <i>Operando</i> X-Ray Absorption Spectroscopy

et al. 2020

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The oxygen chemical potential is an essential indicator for the rate-limiting step of the oxygen reduction reaction in high-temperature electrochemical devices such as solid oxide fuel cells (SOFCs). However, standard electrochemical measurements cannot successfully analyze the oxygen potential profile. Herein, the relationship between oxygen deficiencies and the valence state was determined directly through operando X-ray absorption spectroscopy. To compare the rate-limiting reactions in SOFC cathodes, dense thin-film electrodes of La 0.6 Sr 0.4 CoO 3−δ (LSC) on a Ce 0.9 Gd 0.1 O 1.95 (GDC) electrolyte, La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3−δ (LSCF) on a Y 0.1 Ce 0.9 O 1.95 (YDC) electrolyte, and La 0.9 Sr 0.1 MnO 3+δ (LSM) on a Zr 0.92 Y 0.08 O 1.96 (YSZ) electrolyte were examined as model SOFC cathodes. Variations in the oxygen chemical potential of the electrodes with and without cathodic polarization were experimentally evaluated from the energy shift of the transition metal (Co, Fe, and Mn) K-edge X-ray absorption. It was found that the oxygen chemical potential of the LSC and LSCF electrodes was reduced by applying a cathodic potential and that this change in the oxygen chemical potential occurred mainly on the electrode surface. This result directly demonstrates that the electrochemical oxygen reduction at the cathode is rate-controlled by surface reactions. By contrast, the oxygen potential of LSM changes not at the electrode surface but inside the electrode, which demonstrates that oxide ion diffusion is the rate-determining step for the LSM/YSZ model electrode. This study directly reveals the different rate-determining steps of the electrode reaction for various SOFC cathodes.

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Operando Soft X‐ray Absorption Spectroscopic Study on a Solid Oxide Fuel Cell Cathode during Electrochemical Oxygen Reduction

Cited by 20 publications

References 43 publications

In Situ/Operando Characterization Techniques to Probe the Electrochemical Reactions for Energy Conversion

In Situ/Operando Characterization Techniques to Probe the Electrochemical Reactions for Energy Conversion

In situ and operando characterisation techniques for solid oxide electrochemical cells: recent advances

Investigation of Cathodic Reaction Mechanism in Solid Oxide Fuel Cells by <i>Operando</i> X-Ray Absorption Spectroscopy

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