Evolution of surface and sub-surface morphology and chemical state of exsolved Ni nanoparticles

Kersell, Heath; Weber, Moritz L.; Falling, Lorenz J.; Lu, Qiyang; Baeumer, Christoph; Shirato, Nozomi; Rose, Volker; Lenser, Christian; Gunkel, Felix; Nemšák, Slavomír

doi:10.1039/d1fd00123j

“…Meanwhile, we consider the time when Fe 0 signals first appeared in NAP-XPS (indicated by the arrow in Figure d) to be the exsolution onset time on the STF surface. This is reasonable because previous NAP-XPS studies have successfully correlated the surface metallic species formation to the surface morphology evolution and surface reactivity enhancement during the exsolution process. Therefore, the elapsed time until the first Fe 0 species appeared on the surface indicates how quickly the film reaches the critical oxygen deficiency (i.e., δ 1 in eq ) for exsolution.…”

Section: Resultssupporting

confidence: 68%

“…The prereduction period prior to the exsolution onset is characterized by a continuous intensity decrease in the O 1 s spectra (Figure S3) and a binding energy shift in the XPS spectra (Figure S4), both of which suggest that the STF film kept releasing oxygen upon H 2 reduction. After the exsolution onset, the concentration of surface Fe 0 increases with prolonged reduction time, which reflects the nucleation and growth of exsolved Fe 0 nanoparticles . Therefore, the rate of Fe 0 intensity increase in NAP-XPS can effectively measure the exsolution kinetics.…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, while previous TEM studies were limited to polycrystalline samples, , NAP-XPS can be used to investigate exsolution on single-crystalline samples with well-controlled thickness and orientation, which are essential to quantitatively examine the role of oxygen release kinetics in exsolution. Due to the aforementioned unique advantages, NAP-XPS has gained increasing interest in the field of metal exsolution and has been employed in several studies to investigate the exsolution mechanisms. ,,,− A common practice to date is to use NAP-XPS to probe exsolution while varying the sample temperatures ,, or electrochemical biases. , However, such an experimental protocol cannot be used to investigate the kinetic aspects of exsolution as the thermodynamic driving forces for exsolution kept changing during the course of those experiments. ,,,, To bridge this gap, here we develop a novel experimental method for in situ probing materials’ exsolution kinetics under a constant reduction condition using time-resolved NAP-XPS. As will be elaborated below, this unique experimental approach can not only quantify the concentration of exsolved metallic species as a function of reduction time, but also reveal the prereduction time required to onset metal exsolution with great precision.…”

Section: Introductionmentioning

confidence: 99%

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Fast Surface Oxygen Release Kinetics Accelerate Nanoparticle Exsolution in Perovskite Oxides

Wang

¹

,

Kalaev

²

,

Yang

³

et al. 2023

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Exsolution is a recent advancement for fabricating oxide-supported metal nanoparticle catalysts via phase precipitation out of a host oxide. A fundamental understanding and control of the exsolution kinetics are needed to engineer exsolved nanoparticles to obtain higher catalytic activity toward clean energy and fuel conversion. Since oxygen release via oxygen vacancy formation in the host oxide is behind oxide reduction and metal exsolution, we hypothesize that the kinetics of metal exsolution should depend on the kinetics of oxygen release, in addition to the kinetics of metal cation diffusion. Here, we probe the surface exsolution kinetics both experimentally and theoretically using thin-film perovskite SrTi0.65Fe0.35O3 (STF) as a model system. We quantitatively demonstrated that in this system the surface oxygen release governs the metal nanoparticle exsolution kinetics. As a result, by increasing the oxygen release rate in STF, either by reducing the sample thickness or by increasing the surface reactivity, one can effectively accelerate the Fe0 exsolution kinetics. Fast oxygen release kinetics in STF not only shortened the prereduction time prior to the exsolution onset, but also increased the total quantity of exsolved Fe0 over time, which agrees well with the predictions from our analytical kinetic modeling. The consistency between the results obtained from in situ experiments and analytical modeling provides a predictive capability for tailoring exsolution, and highlights the importance of engineering host oxide surface oxygen release kinetics in designing exsolved nanocatalysts.

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“…Future research is required to clarify the mechanisms of interaction between exsolving species and the surface (defect) chemistry and the resulting electrostatic landscape of perovskite surfaces. Here, in situ analytical techniques may be of major importance to gain a detailed understanding of the structural and chemical evolution of exsolution catalysts over time and according on the processing or operation environment [25][26][27] in order to derive novel strategies for the control of the nanoparticle characteristics at perovskite catalysts that often exhibit a high degree of structural complexity.…”

Section: Discussionmentioning

confidence: 99%

Enhanced metal exsolution at the non-polar (001) surfaces of multi-faceted epitaxial thin films

Weber

¹

,

Kindelmann

²

,

Wessel

³

et al. 2022

Self Cite

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Metal exsolution is a dynamic process that is driven under reducing atomosphere and at elevated temperatures, which results in the self-assembly of nanoparticles at the surface of complex perovskite catalysts. The nanoparticle characteristics of metal exsolution catalysts can be subject to considerable inhomogeneity, where the anisotropic surface properties of ceramic oxides were identified to have a major influence on the exsolution behavior. We systematically reveal the orientation-dependent anisotropy of the exsolution behavior of Ni in SrTi0.9Nb0.05Ni0.05O3-ẟ using multi-faceted epitaxial thin films, that represent a material system with properties in between functional ceramics and single-crystalline perovskite thin film model systems. Using an approach of combined orientation mapping and surface imaging we study the exsolution behavior with particular focus on the initial exsolution reponse i.e. after short annealing times. We find orientation-specific variations in the surface morphology of the thin film facets. In the as-prepared state, surface reconstructions cause the formation of patterned surface structures for all thin film facets apart from (001) surfaces, which exhibit a plain surface morphology as well as an enhanced exsolution response. Surface reconstructions and their inherent energy landscape may hence cause an additional energy barrier for the exsolution reaction that results in orientation-dependent differences in the exsolution kinetics.

show abstract

“…Future research is required to clarify the interaction mechanisms between exsolving species with the surface (defect) chemistry and the resulting electrostatic landscape of perovskite surfaces. Here, in-situ analysis techniques may be of major importance to gain a detailed understanding of the structural and chemical evolution of exsolution catalyst over time and depending on the processing or operation environment [20][21][22] in order to derive novel strategies for the control of the nanoparticle characteristics at perovskite catalysts that oftentimes exhibit a high degree of structural complexity.…”

Section: Discussionmentioning

confidence: 99%

Enhanced metal exsolution at the non-polar (001) surfaces of multi-faceted epitaxial thin films

Weber

¹

,

Kindelmann

²

,

Wessel

³

et al. 2022

Preprint

Self Cite

0

View full text Add to dashboard Cite

Metal exsolution is a dynamic process that is driven under reducing atomosphere and at elevated temperatures, which results in the self-assembly of nanoparticles at the surface of complex perovskite catalysts. The nanoparticle characteristics of metal exsolution catalysts can be subject to considerable inhomogeneity, where the anisotropic surface properties of ceramic oxides were identified to have a major influence on the exsolution behavior. We systematically reveal the orientation-dependent anisotropy of the exsolution behavior of Ni in SrTi0.9Nb0.05Ni0.05O3-ẟ using multi-faceted epitaxial thin films, that represent a material system with properties in between functional ceramics and single-crystalline perovskite thin film model systems. Using an approach of combined orientation mapping and surface imaging we study the exsolution behavior with particular focus on the initial exsolution reponse i.e. after short annealing times. We find orientation-specific variations in the surface morphology of the thin film facets. In the as-prepared state, surface reconstructions cause the formation of patterned surface structures for all thin film facets apart from (001) surfaces, which exhibit a plain surface morphology as well as an enhanced exsolution response. Surface reconstructions and their inherent energy landscape may hence cause an additional energy barrier for the exsolution reaction that results in orientation-dependent differences in the exsolution kinetics.

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Evolution of surface and sub-surface morphology and chemical state of exsolved Ni nanoparticles

Abstract: Dynamic surface and subsurface morphology and chemistry of socketed nanoparticles is monitored in situ for an important emerging class of nanoparticles.

Cited by 7 publications

References 31 publications

Fast Surface Oxygen Release Kinetics Accelerate Nanoparticle Exsolution in Perovskite Oxides

Fast Surface Oxygen Release Kinetics Accelerate Nanoparticle Exsolution in Perovskite Oxides

Enhanced metal exsolution at the non-polar (001) surfaces of multi-faceted epitaxial thin films

Enhanced metal exsolution at the non-polar (001) surfaces of multi-faceted epitaxial thin films

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