Liquid Cell Scanning Transmission Electron Research Articles

Operando Electrochemical Liquid Cell Scanning Transmission Electron Microscopy Investigation of the Growth and Evolution of the Mosaic Solid Electrolyte Interphase for Lithium-Ion Batteries.

The solid electrolyte interphase (SEI) is a key component of a lithium-ion battery forming during the first few dischage/charge cycles at the interface between the anode and the electrolyte. The SEI passivates the anode-electrolyte interface by inhibiting further electrolyte decomposition, extending the battery's cycle life. Insights into SEI growth and evolution in terms of structure and composition remain difficult to access. To unravel the formation of the SEI layer during the first cycles, operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) is employed to monitor in real time the nanoscale processes that occur at the anode-electrolyte interface in their native electrolyte environment. The results show that the formation of the SEI layer is not a one-step process but comprises multiple steps. The growth of the SEI is initiated at low potential during the first charge by decomposition of the electrolyte leading to the nucleation of inorganic nanoparticles. Thereafter, the growth continues during subsequent cycles by forming an island-like layer. Eventually, a dense layer is formed with a mosaic structure composed of larger inorganic patches embedded in a matrix of organic compounds. While the mosaic model for the structure of the SEI is generally accepted, our observations document in detail how the complex structure of the SEI is built up during discharge/charge cycling.

Nonclassical Nucleation and Growth of Pd Nanocrystals from Aqueous Solution Studied by In Situ Liquid Transmission Electron Microscopy

Direct visualization and understanding of the atomic mechanisms governing the growth of nanomaterials are crucial for designing synthesis strategies of high specificity. Aside from playing a key role in numerous technological applications, palladium clusters and nanoparticles are particularly valuable due to their outstanding catalytic activity. Studies show that the properties of Pd nanomaterials depend on shape and size. Therefore, optimizing the synthesis to control the final size and shape of Pd nanoparticles is important for a large number of current and future applications. In this work, we exploit in situ liquid cell scanning transmission electron microscopy to track at the atomic scale the growth of Pd nanoparticles from the very early stage to mature, crystalline nanoparticles. We find that the formation of Pd nanoparticles consists of multiple steps. The first step in nanoparticle formation, representing a nonclassical nucleation step, can be described by the formation of agglomerates of Pd atoms. In the second step, these agglomerates grow via atomic addition to form primary nanoclusters, which coalesce to form amorphous clusters. In the third stage, these clusters continue to coalesce, leading to the formation of amorphous Pd NPs, while in parallel, growth by monomer attachment continues. Then, in the fourth step, the amorphous nanoparticles undergo a nanocrystallization process, where the continuous improvement of crystallinity and the establishment of a distinct morphology eventually give rise to the formation of facetted, crystalline nanoparticles. Similar to our earlier work with Au and Pt nanoparticles, these results confirm that even for simple systems, nonclassical nucleation and growth processes dominate and that these multi-step mechanisms are highly element-specific. Despite the fact that the synthesis conditions are identical, the element-specific interactions define the pathway of the formation of crystalline nanoparticles.

Liquid cell scanning transmission electron microscopy characterization of combined chemical and electrochemical reduction of palladium

We systematically investigate the effect of the driving force on the growth of palladium nanoparticles by comparing electrochemical reduction of polyvinylpyrollidone-stabilized palladium nitrate solution with chemical reduction by ascorbic acid using in-situ liquid cell transmission electron microscopy. Electrochemical data is simultaneously collected while high spatial resolution is maintained. As a chemical reductant, ascorbic acid results in the formation of smaller, more tightly spaced palladium nanoparticles through increased nucleation. When present during electrochemical reduction of palladium, ascorbic acid reduces the degree to which dendrites form due to the growth of a more compact palladium layer. Because the nanoparticles formed during chemical reduction have diameters on the order of a nanometer and are invisible under full liquid conditions, we employ electrochemical water splitting to generate a gas bubble in order to observe the process in real time. This is a step towards real-time characterization of complex solution-phase growth in which multiple pathways exist for metals to reduce and combinations of additives interact to control size and shape.

Discovering the nanoscale origins of localized corrosion in additive manufactured stainless steel 316L by liquid cell transmission electron microscopy

We use liquid cell scanning transmission electron microscopy (STEM) to directly characterize the nanoscale origins of corrosion initiation in Additive manufacturing (AM) 316 L stainless steel. Under applied anodic potentials, we found that the dislocation cellular boundaries were preferentially corroded and that regions of localize corrosion occurred along the cellular boundaries. We directly observed the earliest stages of corrosion by controlling the biasing parameters to decelerate the corrosion processes. The results show that highly localized corrosion occurs via inclusion dissolution along dislocation cell boundaries. More widespread corrosion initiates at the dislocation cell boundaries and spreads throughout the dislocation networks.

Direct Imaging of the Atomic Mechanisms Governing the Growth and Shape of Bimetallic Pt-Pd Nanocrystals by In Situ Liquid Cell STEM.

Understanding the atomic mechanisms governing the growth of bimetallic nanoalloys is of great interest for scientists. As a promising material for photocatalysis applications, Pt-Pd bimetallic nanoparticles (NPs) have been in the spotlight for many years due to their catalytic performance, which is typically superior to that of pure Pt NPs. In this work, we use in situ liquid cell scanning transmission electron microscopy to track the exact atomic mechanisms governing the formation of bimetallic Pt-Pd NPs. We find that the formation process of the bimetallic Pt-Pd is divided into three stages. First, the nucleation and growth of ultrasmall primary nanoclusters are formed by the agglomeration of Pt and Pd atoms. Second, the primary nanoclusters are involved in a coalescence process to form two types of bigger agglomerates, namely, amorphous (a-NC) and crystalline (c-NC) nanoclusters. In the third stage, these clusters undergo a coalescence process leading to the formation of Pt-Pd NPs, while, in parallel, monomer attachment continues. We found that the third stage contains three types of coalescence processes, a-NC-a-NC, a-NC-c-NC, and c-NC-c-NC coalescence, which eventually give rise to crystalline bimetallic alloys. However, each type of coalescence gave distinct NPs in terms of shape and defects. Our results thus reveal the exact growth mechanisms of bimetallic alloys on the atomic scale, unravel the origin of their structure, and overall are of key interest to tailor the structure of bimetallic NPs.

Unraveling the shell growth pathways of Pd-Pt core-shell nanocubes at atomic level by in situ liquid cell electron microscopy

Understanding the formation of core-shell nanomaterials is decisive for controlling their growth, structure, and morphology, which is particularly important in catalysis. As a promising material for photo catalysis application, Pd-Pt core-shell nanoparticles (NPs) have been in the spotlight for many years owing to their catalytic performance typically superior to that of pure Pt nanoparticles. The generation of ultra-thin Pt skins of only a few atomic layers on Pd nanoparticles has turned out to be extremely difficult because Pt tends to form islands during deposition instead of a continuous shell. Therefore, understanding the atomic mechanisms of shell formation is critical for atomic-scale design and control of the platinum shell. Here, by using in situ graphene-based liquid cell scanning transmission electron microscopy (STEM), the growth mechanisms of the Pt shell on Pd nanocubes (NCs) are studied in aqueous solution at the atomic level. Pd-Pt core-shell NPs are formed via two distinct mechanisms: (i) at low concentration of Pt atoms, an ultra-thin skin of only a few atomic layers is formed via atom-by-atom deposition and (ii) at higher concentration of Pt atoms, inhomogeneous islands and thick shells are formed via attachment of Pt clusters. Our study provides a route to control core-shell growth and helps us to understand the exact atomic mechanisms of Pt shell growth on Pd seeds.

Controlling radiolysis chemistry on the nanoscale in liquid cell scanning transmission electron microscopy.

When high-energy electrons from a scanning transmission electron microscope (STEM) are incident on a liquid, the vast majority of the chemical reactions that are observed are induced by the radiolysis breakdown of the liquid molecules. In the study of liquids, the radiolysis products of pure water are well known, and their rate of formation for a given flux of high-energy electrons has been studied intensively over the last few years for uniform TEM illumination. In this paper, we demonstrate that the temporal and spatial distribution of the electron illumination can significantly affect the final density of radiolysis products in water and even change the type of reaction taking place. We simulate the complex array of possible spatial/temporal distributions of electrons that are accessible experimentally by controlling the size, the scan rate and the hopping distance of the electron probe in STEM mode and then compare the results to the uniformly illuminated TEM mode of imaging. By distributing the electron dose both spatially and temporally in the STEM through a randomised "spot-scan" mode of imaging, the diffusion overlap of the radiolysis products can be reduced, and the resulting reactions can be more readily controlled. This control allows the resolution of the images to be separated from the speed of the induced reaction (which is based on beam current alone) and this facet of the experiment will allow a wide range of chemical reactions to be uniquely tailored and observed in all liquid cell STEM experiments.

Spatially Mapping Heterogeneous Nucleation Kinetics of Silver Nanocrystals with Liquid Cell Scanning Transmission Electron Microscopy

Spatially Mapping Heterogeneous Nucleation Kinetics of Silver Nanocrystals with Liquid Cell Scanning Transmission Electron Microscopy

Observing the colloidal stability of iron oxide nanoparticles in situ.

Colloidal processes such as nucleation, growth, ripening, and dissolution are fundamental to the synthesis and application of engineered nanoparticles, as well as numerous natural systems. In nanocolloids consisting of a dispersion of nanoparticles in solution, colloidal stability is influenced by factors including the particle surface facet and capping layer, and local temperature, chemistry, and acidity. In this paper, we investigate colloidal stability through the real-time manipulation of nanoparticles using in situ liquid cell Scanning Transmission Electron Microscopy (STEM). In a distribution of uniform iron oxide nanoparticles, we use the electron beam to precisely control the local chemistry of the solution and observe the critical role that surface chemistry plays in nanoparticle stability. By functionalizing the nanoparticle surfaces with charged amino acids and peptides, stability can be tuned to promote dissolution, growth, or agglomeration, either permanently or reversibly. STEM imaging is used to quantify kinetics of individual nanoparticles subject to local variations in chemistry. These measurements of dissolution and growth rates of iron oxide nanoparticles provide insights into nanoparticle stability relevant to synthesis and functionalization for biomedical applications.

Quantifying the Nucleation and Growth Kinetics of Electron Beam Nanochemistry with Liquid Cell Scanning Transmission Electron Microscopy

In this article, we report on complex nanochemistry and transport phenomena associated with silver nanocrystal formation by electron beam induced growth and liquid cell electron microscopy (LCEM). ...

Anisotropic Nanoscale Galvanic Replacement Reactions Studied by Liquid Cell Scanning Transmission Electron Microscopy

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Operando observations of RuO2 catalyzed Li2O2 formation and decomposition in a Li-O2 micro-battery

RuO2 displays excellent bifunctional catalysis towards the oxygen reduction and evolution reactions of Li-O2 battery. Nevertheless, how the solid catalyst successively catalyzes solid Li2O2 formation and decomposition, confronting passivation and loss of RuO2/Li2O2 contact, during discharging and charging remains a mystery. Here we report operando observations of RuO2 catalyzed oxygen reduction and evolution reactions of Li2O2 by utilizing a liquid cell scanning transmission electron microscope. Upon discharging, RuO2 obviously accelerates formation of soluble LiO2 intermediates and acts as preferential sites of Li2O2 precipitation. During charging, the catalytic activation of RuO2 takes place at electrolyte-RuO2-Li2O2 triple-phase interfaces. Importantly, RuO2 not only catalyzes the decomposition of directly contacted Li2O2, but also promotes oxidation of soluble LiO2 for rapid dissolution of isolated Li2O2 nanoparticles by a chemical comproportionation reaction. The observation unveils how RuO2 catalyzes the formation and decomposition of Li2O2 during discharging and charging and provides nanoscale insights into cathodic reactions of Li-O2 batteries with solid catalysts.

Influence of Cetyltrimethylammonium Bromide on Gold Nanocrystal Formation Studied by In Situ Liquid Cell Scanning Transmission Electron Microscopy

The synthesis of monodisperse size- and shape-controlled Au nanocrystals is often achieved with cetyltrimethylammonium bromide (CTAB) surfactant; however, its role in the growth of such tailored nanostructures is not well understood. To elucidate the formation mechanism(s) and evolution of the morphology of Au nanocrystals in the early growth stage, we present an in situ liquid-cell scanning transmission electron microscopy (STEM) investigation using electron beam-induced radiolytic species as the reductant. The resulting particle shape at a low beam dose rate is shown to be strongly influenced by the surfactant; the Au nanocrystal growth rate is suppressed by increasing the CTAB concentration. At a low CTAB concentration, the nanoparticles (NPs) follow a reaction-limited growth mechanism, while at high a CTAB concentration the NPs follow a diffusion-limited mechanism, as described by the Lifshitz–Slyozov–Wagner (LSW) model. Moreover, we investigate the temporal evolution of specific NP geometries. The am...

Impact of Membrane-Induced Particle Immobilization on Seeded Growth Monitored by In Situ Liquid Scanning Transmission Electron Microscopy.

In situ liquid cell scanning transmission electron microscopy probes seeded growth in real time. The growth of Pd on Au nanocubes is monitored as a model system to compare growth within a liquid cell and traditional colloidal synthesis. Different growth patterns are observed due to seed immobilization and the highly reducing environment within the liquid cell.

Understanding the Role of Solvation Forces on the Preferential Attachment of Nanoparticles in Liquid.

Optimization of colloidal nanoparticle synthesis techniques requires an understanding of underlying particle growth mechanisms. Nonclassical growth mechanisms are particularly important as they affect nanoparticle size and shape distributions, which in turn influence functional properties. For example, preferential attachment of nanoparticles is known to lead to the formation of mesocrystals, although the formation mechanism is currently not well-understood. Here we employ in situ liquid cell scanning transmission electron microscopy and steered molecular dynamics (SMD) simulations to demonstrate that the experimentally observed preference for end-to-end attachment of silver nanorods is a result of weaker solvation forces occurring at rod ends. SMD reveals that when the side of a nanorod approaches another rod, perturbation in the surface-bound water at the nanorod surface creates significant energy barriers to attachment. Additionally, rod morphology (i.e., facet shape) effects can explain the majority of the side attachment effects that are observed experimentally.

Nucleation of iron oxide nanoparticles mediated by Mms6 protein in situ.

Biomineralization proteins are widely used as templating agents in biomimetic synthesis of a variety of organic-inorganic nanostructures. However, the role of the protein in controlling the nucleation and growth of biomimetic particles is not well understood, because the mechanism of the bioinspired reaction is often deduced from ex situ analysis of the resultant nanoscale mineral phase. Here we report the direct visualization of biomimetic iron oxide nanoparticle nucleation mediated by an acidic bacterial recombinant protein, Mms6, during an in situ reaction induced by the controlled addition of sodium hydroxide to solution-phase Mms6 protein micelles incubated with ferric chloride. Using in situ liquid cell scanning transmission electron microscopy we observe the liquid iron prenucleation phase and nascent amorphous nanoparticles forming preferentially on the surface of protein micelles. Our results provide insight into the early steps of protein-mediated biomimetic nucleation of iron oxide and point to the importance of an extended protein surface during nanoparticle formation.

In situ study of oxidative etching of palladium nanocrystals by liquid cell electron microscopy.

Oxidative etching has widely prevailed in the synthesis of a crystal and played a critical role in determining the final growth behavior. In this Letter, we report an in situ microscopic study on the oxidative etching of palladium cubic nanocrystals by liquid cell scanning transmission electron microscopy. The etching was realized with oxidative radiation reactants from electron-water interaction in the presence of Br(-) ions. Dissolution dynamics of monodispersed and aggregated nanocrystals were both investigated and compared. Analyses on the dissolution kinetics of nanocrystals and the diffusion kinetics of the dissolved agents were carried out based on the scanning transmission electron microscopy characterizations. The results presented here pave a way toward the quantitative understanding of the oxidative etching reaction and its application in the functionally orientated fabrication of nanocrystals with certain sizes, structures, and morphologies.