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Direct Observation of Structural Evolution of Metal Chalcogenide in Electrocatalytic Water Oxidation
摘要： As one of the most remarkable oxygen evolution reaction (OER) electrocatalysts, metal chalcogenides have been intensively reported due to their high OER activities during the past few decades. It has been reported that electron-chemical conversion of metal chalcogenides into oxides/hydroxides would take place after OER. However, the transition mechanism of such unstable structures, as well as the real active sites and catalytic activity during OER for these electrocatalysts, has not been understood yet, which urgently needs a direct observation for the electrocatalytic water oxidation process, especially at nano or even angstrom scale. In this research, by employing advanced Cs-corrected transmission electron microscopy (TEM), a step by step oxidational evolution of amorphous electrocatalyst CoSx into crystallized CoOOH in OER has been in situ captured: irreversible conversion of CoSx to crystallized CoOOH is initiated on the surface of electrocatalysts with a morphology change via Co(OH)2 intermediate during OER measurement, where CoOOH is confirmed as the real active species. Besides, this transition process has also been confirmed by multiple applications of X-ray photoelectron spectroscopy (XPS), in situ Fourier-transform infrared spectroscopy (FTIR) and other ex situ technologies. Moreover, based on this discovery, a high-efficiency electrocatalyst of a nitrogen-doped graphene foam (NGF) coated by CoSx has been explored through a thorough structure transformation of CoOOH. We believe this in situ and in-depth observation of structural evolution in OER measurement can provide insights into the fundamental understanding of the mechanism for OER catalysts, thus enabling the more rational design of low-cost and high-efficient electrocatalysts for water splitting.
关键词： structural evolution,XPS,in situ TEM,water oxidation,cobalt chalcogenide
更新于2025-11-14 15:27:09
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Structural Evolutions of Vertically-Aligned Two-Dimensional MoS <sub/>2</sub> Layers Revealed by <i>In Situ</i> Heating Transmission Electron Microscopy
摘要： Benefited from a large density of layer edges exposed on the surface, vertically-aligned two-dimensional (2D) molybdenum disulfide (MoS2) layers have recently harvested excellent performances in the field of electrochemical catalysis and chemical sensing. With their increasing versatility for high-temperature demanding applications, it is vital to identify their thermally-driven structural and chemical stability as well as clarify its underlying principle. Despite various ex situ and in situ characterizations on horizontally-aligned 2D MoS2 layers, the direct in situ heating of vertically-aligned 2D MoS2 layers and the real-time observation of their near-atomic scale dynamics have never been approached, leaving their thermal stability poorly understood. Moreover, the geometrical advantage of the surface-exposed vertically-aligned 2D MoS2 layers is anticipated to unveil the structural dynamics of interlayer van der Waals (vdW) gaps and its correlation with thermal energy, unattainable with 2D MoS2 layers in any other geometry. Herein, we report a comprehensive in situ heating TEM study on cleanly transferred vertically-aligned 2D MoS2 layers up to 1000 °C. Several striking phenomena were newly observed in the course of heating: (1) formation and propagation of voids between the domains of vertical 2D MoS2 layers with distinct grain orientations starting at ~875 °C, (2) subsequent decompositions of the 2D MoS2 layers accompanying a formation of Mo nanoparticles at ~950 °C, much lower than the melting temperature of their bulk counterpart, and (3) initiation of decomposition from the surface-exposed 2D layer vertical edge sites, congruently supported by molecular dynamics (MD) simulation. These new findings will offer critical insights into better understanding the thermodynamic principle that governs the structural stability of general vdW 2D crystals as well as providing useful technological guidance for materials design and optimization in their potential high-temperature applications.
关键词： van der Waals gaps,in situ heating,structural evolution,MoS2,two-dimensional,vertically-aligned,transmission electron microscopy,thermal stability,molecular dynamics simulation
更新于2025-09-23 15:19:57
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Design of a Broadband NIR Phosphor for Security-Monitoring LEDs: Tunable Photoluminescence Properties and Enhanced Thermal Stability
摘要： Near-infrared (NIR) phosphors with capability for blue light to 850 nm broadband NIR emission conversion are highly desirable for security-monitoring LEDs. Targeted phosphor LaSc2.93-yGayB4O12(LSGB): 0.07Cr3+ (y = 0.6) is designed from the initial model of LaSc2.93B4O12(LSB): 0.07Cr3+ by chemical composition modification. The correlations among crystal-field environment, structural evolution, and luminescence properties of LSGB: 0.07Cr3+ (0 ≤ y ≤ 1.5) are elucidated by the Dq/B values, decay curves, and polyhedron distortion. The substitution of Sc3+ by Ga3+ in LSGB: Cr3+ (0 ≤ y ≤ 1.5) leads to decreasing structural polyhedron distortion and strengthened crystal field, consequently resulting in the blue-shift of broadband emission and enhanced thermal stability of LSGB: 0.07Cr3+ (y = 0.6) compared to that of LSB: 0.07Cr3+. The above results demonstrate that the superiority of blue-shift and enhanced thermal stability of LSGB: 0.07Cr3+ (y = 0.6) make it more suitable for the blue-pumped security-monitoring LEDs.
关键词： luminescence properties,crystal-field environment,security-monitoring LEDs,thermal stability,structural evolution,LaSc2.93-yGayB4O12(LSGB): 0.07Cr3+,Near-infrared (NIR) phosphors
更新于2025-09-23 15:19:57
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Growth-Rule-Guided Structural Exploration of Thiolate-Protected Gold Nanoclusters
摘要： Understanding the structure and structure?property relationship of atomic and ligated clusters is one of the central research tasks in the field of cluster research. In chemistry, empirical rules such as the polyhedral skeleton electron pair theory (PSEPT) approach had been outlined to account for skeleton structures of many main-group atomic and ligand-protected transition metal clusters. Nonetheless, because of the diversity of cluster structures and compositions, no uniform structural and electronic rule is available for various cluster compounds. Exploring new cluster structures and their evolution is a hot topic in the field of cluster research for both experiment and theory. In this Account, we introduce our recent progress in the theoretical exploration of structures and evolution patterns of a class of atomically precise thiolate-protected gold nanoclusters using density functional theory computations. Unlike the conventional ligand-protected transition metal compounds, the thiolate-protected gold clusters demonstrate novel metal core/ligand shell interfacial structures in which the Aum(SR)n clusters can be divided into an ordered Au(0) core and a group of oligomeric SR[Au(SR)]x (x = 0, 1, 2, 3, ...) protection motifs. Guided by this “inherent structure rule”, we have devised theoretical methods to rapidly explore cluster structures that do not necessarily require laborious global potential energy surface searches. The structural predictions of Au38(SR)24, Au24(SR)20, and Au44(SR)28 nanoclusters were completely or partially verified by the later X-ray crystallography studies. On the basis of the analysis of cluster structures determined by X-ray crystallography and theoretical prediction, a structural evolution diagram for the face-centered-cubic (fcc)-type Aum(SR)n clusters with m up to 92 has been preliminarily established. The structural evolution diagram indicates some basic structural and electronic evolution patterns of thiolate-protected gold nanoclusters. The fcc Aum(SR)n clusters show a genetic structural evolution pattern in which each step of cluster size increase results in the formation of another Au4 tetrahedron or Au3 triangle unit in the Au core, and every increase of a structural unit in the Au core leads to an increase of two electrons in the whole cluster. The unique one- or two-dimensional cluster size evolution, the isomerism of the Au?S framework, and the formation of a double-helical and cyclic tetrahedron network in the fcc Aum(SR)n clusters all can be addressed from this evolution pattern. The summarized cluster structural evolution diagrams enable us to further explore more stable cluster structures and understand their structure?electronic structure?property relationships.
关键词： face-centered-cubic,thiolate-protected gold nanoclusters,density functional theory,electronic structure,structural evolution
更新于2025-09-23 15:19:57