Particle-Support Interferences in Small-Angle X-Ray Scattering from Supported-Catalyst Materials

Binninger, Tobias; Garganourakis, Marios; Han, Jun; Pătru, Alexandra; Fabbri, Emiliana; Sereda, Olha; Kötz, R.; Menzel, Andreas; Schmidt, Thomas J.

doi:10.1103/physrevapplied.3.024012

Cited by 26 publications

(37 citation statements)

References 23 publications

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“…At the same time, the depression of scattering intensity resulting from the particle-support interference effect gets weaker because of the decreasing difference between support particle size and Pt particle size. 9 The growth of Pt nanoparticles in the course of high-potential cycling is obvious from the log-normal Pt nanoparticle size distributions shown in Figure 6b. The narrow initial distribution at an average diameter ofd 0 = 2.2 nm collapses after the first high-potential cycle and continues to get broader and to shift to larger diameters to reach an average diameter ofd 500 = 4.4 nm after 500 degradation cycles.…”

Section: Resultsmentioning

confidence: 99%

“…As described in detail in Ref. 9, SAXS curves at four different X-ray energies close to the Pt-L III absorption edge were used in the analysis, and the resulting net Pt signal was fitted with the standard model of spherical Pt particles with log-normal size distribution in combination with the model for the Pt particle-support material scattering interference presented in the same reference.…”

Section: Methodsmentioning

confidence: 99%

“…Finally, the tunability of the X-ray photon energy at synchrotron sources enables the use of anomalous SAXS (ASAXS) in order to extract elementspecific structural information. 8 The energy-dependent variation of the X-ray scattering cross section of Pt close to the Pt-L III absorption edge can be used to separate the Pt nanoparticle scattering from the scattering of the support material 9 even for the strongly scattering IrO 2 -TiO 2 support material of the catalyst presented in Figure 1b.…”

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confidence: 99%

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Electrochemical Flow-Cell Setup for In Situ X-ray Investigations

Binninger

Fabbri

Pătru

et al. 2016

J. Electrochem. Soc.

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109

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An electrochemical three-electrode flow-cell is presented for in situ small-angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) experiments in transmission mode at synchrotron X-ray sources. The cell also allows for in situ XAS performed in fluorescence mode. Constant experimental conditions, even under moderate gas evolution, are provided by the electrolyte flow with controlled gas saturation. A special configuration of working and counter electrode, respectively, yields low residual ohmic resistance in three-electrode measurements that enables the study of thick porous electrodes of active high surface area materials. The cell proved its functionality and reliability in two studies: First, an in situ anomalous SAXS experiment for the high-potential degradation properties of a Pt/IrO 2 -TiO 2 catalyst for the oxygen reduction reaction at polymer electrolyte fuel cell cathodes; and second, an in situ XAS study of the electronic state of Ir centers inside an IrO 2 -TiO 2 catalyst under oxygen evolution conditions. © The Author Modern research in electrocatalysis makes extensive use of in situ X-ray techniques that provide information about the structure and the electronic state of catalyst materials under electrochemical potential control. The reason for this is the limited, merely indirect information about the state of the catalyst that can be deduced from purely electrochemical testing like cyclic voltammetry (CV) which often does not allow for an unambiguous interpretation of the data. In order to develop an understanding at a more fundamental level, additional information is required about the potential-dependent state of electrocatalyst materials that can be provided by synchrotron-based techniques like X-ray scattering or X-ray absorption spectroscopy.One example is the investigation of polymer electrolyte fuel cell (PEFC) Pt cathode catalyst degradation. Different mechanisms have been proposed for the loss of electrochemically active Pt surface area (ECSA) that occurs most severely at transient high-potential spikes during PEFC start and stop.1,2 Processes like agglomeration of primary Pt particles due to migration or carbon support corrosion, Pt loss due to dissolution, and growth of primary Pt nanoparticles due to dissolution/redeposition cycles have been considered 3,4 and quantified for different operation conditions and electrochemical environments. The most common technique applied for this purpose is transmission electron microscopy (TEM), which has the convenient advantage that changes of the Pt nanoparticle structure can be directly visualized, especially with the use of identical location TEM (IL-TEM).5 Although successfully demonstrated, 6 in situ TEM remains limited to certain electrochemical systems. Whereas the strength of TEM lies in the direct imaging of individual catalyst particles, it is challenging to extract quantitative statistical information about the entire catalyst sample from TEM analysis. Finally, the distinction of Pt nanoparticles from the support material p...

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Electrochemical Flow-Cell Setup for In Situ X-ray Investigations

Binninger

Fabbri

Pătru

et al. 2016

J. Electrochem. Soc.

Self Cite

109

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“…22 The proportionality factor was obtained from the ratio of the integrated scattering data measured for this glassy carbon sample with our MPD setup and the known differential cross section per area of this sample integrated over the same q-range, the atomic form factor of Pt at the given X-ray energy, n Pt the atomic (number) density of Pt and S Pt (q) the partial structure factor (PSF) of the Pt-NPs. 17 The model of spherical particles was used for the analysis of the net Pt differential cross sections extracted from our experimental data. Within this model, the Pt PSF is given by S Pt (q) = N Pt Due to the absolute normalization of the scattering data to differential cross sections, results from the fit not only allowed to determine the log-normal size distribution of the Pt-NPs P Pt (R Pt ), but also to assess the absolute number of Pt-NPs per electrode area where ρ Pt is the mass density of platinum.…”

Section: Discussionmentioning

confidence: 99%

“…Finally, the tunability of X-ray photon energy at synchrotron sources enables the use of anomalous SAXS (ASAXS) in order to separate the Pt nanoparticle (Pt-NP) scattering from the background scattering from support material and cell components. 9,17 Despite these advantages, in situ SAXS experiments at synchrotron facilities face the major drawback of highly restricted availability of beamtime. Multi-purpose laboratory X-ray diffractometers represent an attractive alternative to perform electrochemical in situ SAXS experiments due to their widespread availability.…”

mentioning

confidence: 99%

Electrochemical Flow-Cell Setup for In Situ X-ray Investigations

Tillier

Binninger

Garganourakis

et al. 2016

J. Electrochem. Soc.

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A unique electrochemical three-electrode flow-cell design is presented for in situ small-angle X-ray scattering experiments on a multi-purpose laboratory X-ray diffractometer. An electrolyte layer thickness of 2 mm enables sufficient photon transmission to acquire in situ scattering curves at high signal-to-noise ratio within less than one hour despite the restricted photon flux from a standard Cu X-ray tube. Complete tightness of the cell allows electrolyte flow with controlled gas saturation in order to guarantee constant experimental conditions even for long experimental protocols. Good electrochemical performance is achieved by a special arrangement of working and counter electrodes that are deposited on the opposing X-ray transmission windows of the cell. The functionality and reliability of the cell are demonstrated in an in situ small-angle X-ray scattering study of the degradation properties of carbon-supported Pt nanoparticles during electrochemical high-potential cycling. Careful subtraction of background scattering and absolute normalization of the scattering curves yield absolute quantitative structural information about the Pt nanoparticle phase at different stages of the degradation protocol, bringing insights into the real-time evolution during electrochemical characterization. The need for high-efficiency and non-polluting energy conversion technologies for automotive applications has resulted in an increasing interest in polymer electrolyte fuel cells (PEFCs). One critical issue facing the commercialization of PEFCs is the gradual decline in performance resulting in a severe limitation of PEFC lifetime. 1,2 One important cause of PEFC performance degradation is the loss of electrochemically active surface area (ECSA) of the supported platinum nanoparticles (Pt-NPs) at the cathode. This ECSA decrease of the cathode catalyst can arise from different degradation mechanisms which take place simultaneously, especially during PEFC start and stop events, when the cathode potential can reach very high transient values up to 1.4-1.5 V RHE . 3 In situ analytical tools are required to gain a better understanding of the phenomena involved and to distinguish between different degradation mechanisms like platinum loss due to dissolution, nanoparticle growth resulting from electrochemical Ostwald ripening or platinum nanoparticle agglomeration due to support material corrosion. [4][5][6][7][8] Electrochemical in situ small angle X-ray scattering (in situ SAXS) offers the unique opportunity not only to observe the evolution of the platinum nanoparticle size distribution during an electrochemical degradation experiment, but also to simultaneously monitor the evolution of the absolute platinum mass content of the electrode. In situ SAXS experiments can be conveniently performed at synchrotron X-ray sources. [9][10][11][12][13][14][15][16] The high photon flux from these radiation sources yields a very good scattering signal-to-noise ratio in a short acquisition time despite the strong X-ray absorption of the elec...

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Shedding Light on Electrocatalysts: Practical Considerations for Operando Studies with High‐Energy X‐Rays

Pittkowski

2024

ChemElectroChem

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Operando studies using high‐energy X‐rays from synchrotron sources are essential for unraveling the complex material transformation that electrocatalysts undergo under operating conditions. This article explores key considerations to perform these experiments and the insights gained from such studies on nanostructured electrocatalysts. Critical factors include optimizing electrochemical performance while obtaining high‐quality X‐ray signals, which often require compromises. The electrochemical operando cell design is crucial, and several different cells are discussed here. Working electrode geometries parallel to the X‐ray beam, probed with a microfocused beam, are emerging as promising solutions for realistic electrochemical performance in operando cells. Careful attention must also be paid to the electrochemical measuring conditions, electrode loading, and beam damage to ensure reliable experiments. When carefully performed and by combining multiple characterization techniques, operando studies with high‐energy X‐rays offer the unique possibility to fully understand the structure of the active electrocatalyst.

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Particle-Support Interferences in Small-Angle X-Ray Scattering from Supported-Catalyst Materials

Cited by 26 publications

References 23 publications

Electrochemical Flow-Cell Setup for In Situ X-ray Investigations

Electrochemical Flow-Cell Setup for In Situ X-ray Investigations

Electrochemical Flow-Cell Setup for In Situ X-ray Investigations

Shedding Light on Electrocatalysts: Practical Considerations for Operando Studies with High‐Energy X‐Rays

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