<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe₂O₃/Graphene Anode during Lithiation–Delithiation Processes

Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe₂O₃/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe₂O₃ nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li₂O layer. Single-crystalline Fe₂O₃ nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li₂O matrix. Surprisingly, the delithiated product was not Fe₂O₃ but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe₂O₃ in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li₂O layer. The macroscopic electrochemical performance of Fe₂O₃/graphene was further correlated with the microcosmic <i>in situ</i> TEM results

In Situ Transmission Electron Microscopy Observation of the Lithiation–Delithiation Conversion Behavior of CuO/Graphene Anode

The electrochemical conversion behavior of metal oxides as well as its influence on the lithium-storage performance remains unclear. In this paper, we studied the dynamic electrochemical conversion process of CuO/graphene as anode by in situ transmission electron microscopy. The microscopic conversion behavior of the electrode was further correlated with its macroscopic lithium-storage properties. During the first lithiation, the porous CuO nanoparticles transformed to numerous Cu nanograins (2–3 nm) embedded in Li₂O matrix. The porous spaces were found to be favorable for accommodating the volume expansion during lithium insertion. Two types of irreversible processes were revealed during the lithiation–delithiation cycles. First, the nature of the charge–discharge process of CuO anode is a reversible phase conversion between Cu₂O and Cu nanograins. The delithiation reaction cannot recover the electrode to its pristine structure (CuO), which is responsible for about ∼55% of the capacity fading in the first cycle. Second, there is a severe nanograin aggregation during the initial conversion cycles, which leads to low Coulombic efficiency. This finding could also account for the electrochemical behaviors of other transition metal oxide anodes that operate with similar electrochemical conversion mechanism

<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe₂O₃/Graphene Anode during Lithiation–Delithiation Processes

Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe₂O₃/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe₂O₃ nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li₂O layer. Single-crystalline Fe₂O₃ nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li₂O matrix. Surprisingly, the delithiated product was not Fe₂O₃ but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe₂O₃ in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li₂O layer. The macroscopic electrochemical performance of Fe₂O₃/graphene was further correlated with the microcosmic <i>in situ</i> TEM results

<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe₂O₃/Graphene Anode during Lithiation–Delithiation Processes

Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe₂O₃/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe₂O₃ nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li₂O layer. Single-crystalline Fe₂O₃ nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li₂O matrix. Surprisingly, the delithiated product was not Fe₂O₃ but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe₂O₃ in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li₂O layer. The macroscopic electrochemical performance of Fe₂O₃/graphene was further correlated with the microcosmic <i>in situ</i> TEM results

<i>In Situ</i> Transmission Electron Microscopy Observation of the Conversion Mechanism of Fe₂O₃/Graphene Anode during Lithiation–Delithiation Processes

Transition metal oxides have attracted tremendous attention as anode materials for lithium ion batteries (LIBs) recently. However, their electrochemical processes and fundamental mechanisms remain unclear. Here we report the direct observation of the dynamic behaviors and the conversion mechanism of Fe₂O₃/graphene in LIBs by <i>in situ</i> transmission electron microscopy (TEM). Upon lithiation, the Fe₂O₃ nanoparticles showed obvious volume expansion and morphological changes, and the surfaces of the electrode were covered by a nanocrystalline Li₂O layer. Single-crystalline Fe₂O₃ nanoparticles were found to transform to multicrystalline nanoparticles consisting of many Fe nanograins embedded in Li₂O matrix. Surprisingly, the delithiated product was not Fe₂O₃ but FeO, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle. The charge–discharge processes of Fe₂O₃ in LIBs are different from previously recognized mechanism, and are found to be a fully reversible electrochemical phase conversion between Fe and FeO nanograins accompanying the formation and disappearance of the Li₂O layer. The macroscopic electrochemical performance of Fe₂O₃/graphene was further correlated with the microcosmic <i>in situ</i> TEM results

Magnetic and Quantum Transport Properties of Small-Sized Transition-Metal-Pentalene Sandwich Cluster

The chemical bonds and magnetic and quantum transport properties of small-sized transition-metal-pentalene sandwich clusters TM_2<i>n</i>Pn_<i>n</i>+1 (TM = V, Cr, Mn, Co, and Ni; <i>n</i> = 1, 2) were investigated by using density functional theory and nonequilibrium Green’s function method. Theoretical results show that TM_2<i>n</i>Pn_<i>n</i>+1 sandwiches have high stabilities. The TM–TM bond order gradually decreases with the increase of 3d electron number of TM atoms and TM_2<i>n</i>Pn_<i>n</i>+1 could exhibit different spin states. With Au as two electrodes, significant spin-filter capability was observed in TM_2<i>n</i>Pn_<i>n</i>+1, and such a filter can be switched on/off by changing the spin state. In addition, giant magnetoresistance was also found in the systems. These interesting quantum transport properties indicate that TM_2<i>n</i>Pn_<i>n</i>+1 sandwiches are promising materials for designing molecular junction with different functions

Determination of allura red using composites of water-dispersible reduced graphene oxide-loaded Au nanoparticles based on ionic liquid

A facile route for producing reduced graphene oxide (RGO)-loaded Au nanoparticles based on ionic liquids (IL) has been proposed, in which the as-prepared RGO can be dispersed stably in water. With the assistance of IL, Au nanoparticles were uniformly and densely absorbed on the surfaces of the IL functionalised reduced graphene oxide (IRGO), forming a new composite of IRGO/Au with high dispersibility. This IRGO/Au composite enhanced its electrochemical signal obviously in the measurement of allura red in foods and exhibited a wider linear response ranging from 0.297 (0.0006 μmol L−1) to 99.3 μg L−1 (0.2 μmol L−1) with lower detection limit of 0.213 μg L−1 (0.00043 μmol L−1) at a signal-to-noise ratio of 3. To further study the practical applicability of the proposed sensor, the modified electrode was successfully applied to detect allura red in five kinds of common foods and the assay results were in a good agreement with the reference values detected by HPLC.</p

Silver Nanoparticle-Modified Black Phosphorus for Photocatalytic Properties

Single-element phosphorus is an emerging class of two-dimensional (2D) semiconductor materials that has attracted extensive attention, particularly as a photocatalyst material. However, the inherent instability of elemental phosphorus causes insufficient surface activity for photocatalytic performance. In this study, the self-adsorption and clustering of metal ions on the surface of 2D materials were exploited to form Ag nanoparticle (NP)-modified black phosphorus (BP-Ag) heterostructures, which passivated the lone-pair electrons of phosphorus, promoted charge separation, and enhanced the photocatalytic activity. Consequently, the photocatalytic decomposition of methyl orange with BP-Ag was 99.05%, which was 1.87 times higher than that of pure black phosphorus. Within 3 h, the photocatalytic hydrogen evolution efficiency of BP modified by Ag NPs was about 20 times that of BP. In addition, the decomposition of dye molecules was investigated using active substances, such as hydroxyl radicals, superoxide radicals, and holes. In conclusion, the modification of metal NPs can greatly improve the stability and photocatalytic performance of single-element phosphorus materials, which has good application prospects for purifying dye wastewater and hydrogen evolution

DataSheet1_Influence of Colonies’ Morphological Cues on Cellular Uptake Capacity of Nanoparticles.DOCX

High transmembrane delivery efficiency of nanoparticles has attracted substantial interest for biomedical applications. It has been proved that the desired physicochemical properties of nanoparticles were efficient for obtaining a high cellular uptake capacity. On the other hand, biophysical stimuli from in situ microenvironment were also indicated as another essential factor in the regulation of cellular uptake capacity. Unfortunately, the influence of colony morphology on cellular uptake capacity was rarely analyzed. In this study, micropatterned PDMS stencils containing circular holes of 800/1,200 μm in diameter were applied to control colonies’ size. The amino-modified nanoparticles were cocultured with micropatterned colonies to analyze the influence of colonies’ morphology on the cellular uptake capacity of nanoparticles. Consequently, more endocytosed nanoparticles in larger colonies were related with a bigger dose of nanoparticles within a larger area. Additionally, the high cell density decreased the membrane–nanoparticles’ contacting probability but enhanced clathrin-mediated endocytosis. With these contrary effects, the cells with medium cell density or located in the peripheral region of the micropatterned colonies showed a higher cellular uptake capacity of nanoparticles.</p

In Situ Transmission Electron Microscopy Observation of Electrochemical Behavior of CoS₂ in Lithium-Ion Battery

Metal sulfides are a type of potential anode materials for lithium-ion batteries (LIBs). However, their electrochemical behaviors and mechanism during the charge and discharge process remain unclear. In the present paper, we use CoS₂ as a model material to investigate their electrochemical process using in situ transmission electron microscopy (TEM). Two kinds of reaction behaviors are revealed. The pure CoS₂ particles show a side-to-side conversion process, in which large and anisotropic size expansion (47.1%) occurs that results in the formation of cracks and fractures in CoS₂ particles. In contrast, the CoS₂ particles anchored on reduced graphene oxide (rGO) sheets exhibit a core–shell conversion process involving small and homogeneous size expansion (28.6%) and few fractures, which attributes to the excellent Li⁺ conductivity of rGO sheets and accounts for the improved cyclability. Single-crystalline CoS₂ particle converts to Co nanocrystals of 1–2 nm embedded within Li₂S matrix after the first lithiation. The subsequent electrochemical reaction is a reversible phase conversion between Co/Li₂S and CoS₂ nanocrystals. Our direct observations provide important mechanistic insight for developing high-performance conversion electrodes for LIBs