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Creators/Authors contains: "Yang, Shize"

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  6. Abstract

    2D Janus Transition Metal Dichalcogenides (TMDs) have attracted much interest due to their exciting quantum properties arising from their unique two‐faced structure, broken‐mirror symmetry, and consequent colossal polarization field within the monolayer. While efforts are made to achieve high‐quality Janus monolayers, the existing methods rely on highly energetic processes that introduce unwanted grain‐boundary and point defects with still unexplored effects on the material's structural and excitonic properties Through high‐resolution scanning transmission electron microscopy (HRSTEM), density functional theory (DFT), and optical spectroscopy measurements; this work introduces the most encountered and energetically stable point defects. It establishes their impact on the material's optical properties. HRSTEM studies show that the most energetically stable point defects are single (VS andVSe) and double chalcogen vacancy (VSVSe), interstitial defects (Mi), and metal impurities (MW) and establish their structural characteristics. DFT further establishes their formation energies and related localized bands within the forbidden band. Cryogenic excitonic studies on h‐BN‐encapsulated Janus monolayers offer a clear correlation between these structural defects and observed emission features, which closely align with the results of the theory. The overall results introduce the defect genome of Janus TMDs as an essential guideline for assessing their structural quality and device properties.

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  7. Abstract

    An ultra‐fast electrochemical capacitor (EC) designed for efficient ripple current smoothing was fabricated using vertically oriented MoS2(VOM) nanoflakes deposited on freestanding carbonized cellulose (CC) sheets as electrodes. The daily used cellulose tissue sheets were transformed into electrode scaffolds through a rapid pyrolysis process within a preheated furnace, on which VOM nanoflakes were formed in a conventional hydrothermal process. With these ~10 μm thick VOM‐CC electrodes, ultrafast ECs with tunable frequency response and specific capacitance density were fabricated. The ECs with a cell‐level areal capacitance density of 0.8 mF/cm2at 120 Hz were demonstrated for ripple current filtering from 60 Hz to 60 kHz. At a lower frequency response level, EC cell with a large capacitance density of 4.8 mF/cm2was also demonstrated. With the facile and easily scaled up process to producing the nanostructured electrode, the miniaturized VOM‐CC based ECs have the potential to substitute the bulky aluminum electrolytic capacitors for current smoothing and pulse power applications.

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  8. Abstract

    Overcoming slow kinetics and high overpotential in electrocatalytic oxygen evolution reaction (OER) requires innovative catalysts and approaches that transcend the scaling relationship between binding energies for intermediates and catalyst surfaces. Inorganic complexes provide unique, customizable geometries, which can help enhance their efficiencies. However, they are unstable and susceptible to chemical reaction under extreme pH conditions. Immobilizing complexes on substrates creates single‐molecule catalysts (SMCs) with functional similarities to single‐atom catalysts (SACs). Here, an efficient SMC, composed of dichloro(1,3‐bis(diphenylphosphino)propane) nickel [NiCl2dppp] anchored to a graphene acid (GA), is presented. This SMC surpasses ruthenium‐based OER benchmarks, exhibiting an ultra‐low onset and overpotential at 10 mAcm−2when exposed to a static magnetic field. Comprehensive experimental and theoretical analyses imply that an interfacial charge transfer from the Ni center in NiCl2dppp to GA enhances the OER activity. Spectroscopic investigations reveal an in situ geometrical transformation of the complex and the formation of a paramagnetic Ni center, which under a magnetic field, enables spin‐selective electron transfer, resulting in enhanced OER performance. The results highlight the significance of in situ geometric transformations in SMCs and underline the potential of an external magnetic field to enhance OER performance at a single‐molecule level.

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