Showing papers by "Miaofang Chi published in 2023"
TL;DR: In this paper , a photocatalyst with a self-grown TiO2/Ti-metal-organic framework (MOF) heterojunction was developed, where Pt is selectively anchored on Ti-BPDC by ligands.
Abstract: A photocatalyst TiO2/Ti-BPDC-Pt is developed with a self-grown TiO2/Ti-metal-organic framework (MOF) heterojunction, i.e., TiO2/Ti-BPDC, and selectively anchored high-density Pt single-atomic cocatalysts on Ti-BPDC for photocatalytic hydrogen evolution. This intimate heterojunction, growing from the surface pyrolytic reconstruction of Ti-BPDC, works in a direct Z-scheme, efficiently separating electrons and holes. Pt is selectively anchored on Ti-BPDC by ligands and is found in the form of single atoms with loading up to 1.8 wt.%. The selective location of Pt is the electron-enriched domain of the heterojunction, which further enhances the utilization of the separated electrons. This tailored TiO2/Ti-BPDC-Pt shows a significantly enhanced activity of 12.4 mmol g-1 h-1 compared to other TiO2- or MOF-based catalysts. The structure-performance relationship further proves the balance of two simultaneously exposed domains of heterojunctions is critical to fulfilling this kind of catalyst.
1 citations
TL;DR: In this article , the electrochemical transformation of CO2 to highly crystalline nano-graphite with a controlled microstructure in a carbonate molten salt at 780 °C was investigated as an anode material for lithium-ion batteries.
1 citations
TL;DR: In this article , the structural evolution of the Ru/Ca2N:e− catalyst during the ammonia synthesis reaction was investigated by in situ neutron scattering (inelastic neutron scattering, INS) technique.
Abstract: NH3 synthesis is one of the most critical industrial processes. Compared to commercial iron catalysts, Ru catalysts show high intrinsic activity in this reaction but suffer from hydrogen poisoning. By loading Ru onto supports such as electrides and hydrides, the hydrogen poisoning problem can be significantly alleviated. However, relevant studies on the structural dynamics of the Ru/electride catalysts under reaction conditions are very scarce. Taking advantage of the high sensitivity to hydrogen species, it is possible to obtain insights into the structural changes during the reaction using in situ neutron techniques. In this study, we have investigated the structural evolution of the Ru/Ca2N:e– catalyst during the ammonia synthesis reaction by in situ neutron scattering (inelastic neutron scattering, INS) technique. In situ INS experiments suggest that Ca2N:e– is likely converted to the Ca2NH phase during the reaction. Unlike the previously known structure where H and N atoms are intermixed, the formed Ca2NH exhibits a segregated structure where the H and N atoms are located in different layers separated by the Ca layer. Density functional theory calculations of the reaction energetics reveal that there are minor changes in the barriers and thermodynamics of the first N hydrogenation step between the two phases (Ca2NH phase with segregated H/N layers and intermixed Ca2NH phase), suggesting the impact of the phases on the reaction kinetics to be relatively minimal.
1 citations
TL;DR: In this article , the structural information beyond the diffraction-limit and chemical information from the material can be extracted together, resulting in simultaneous multi-modal measurements, adding the additional dimensions of spectral information to 4D datasets.
Abstract: With the recent development of high-acquisition-speed pixelated detectors, 4D scanning transmission electron microscopy (4D-STEM) is becoming routinely available in high-resolution electron microscopy. 4D-STEM acts as a “universal” method that provides local information on materials that is challenging to extract from bulk techniques. It extends conventional STEM imaging to include super-resolution techniques and to provide quantitative phase-based information, such as differential phase contrast, ptychography, or Bloch wave phase retrieval. However, an important missing factor is the chemical and bonding information provided by electron energy loss spectroscopy (EELS). 4D-STEM and EELS cannot currently be acquired simultaneously due to the overlapping geometry of the detectors. Here, the feasibility of modifying the detector geometry to overcome this challenge for bulk specimens is demonstrated, and the use of a partial or defective detector for ptycholgaphic structural imaging is explored. Results show that structural information beyond the diffraction-limit and chemical information from the material can be extracted together, resulting in simultaneous multi-modal measurements, adding the additional dimensions of spectral information to 4D datasets.
TL;DR: In this paper, a nonrigid registration is used to identify localized distortions in a 4D-STEM image and relate them to an undistorted experimental STEM image, followed by a series of affine transformations for distortion corrections.
Abstract: Cryogenic four-dimensional scanning transmission electron microscopy (4D-STEM) imaging is a useful technique for studying quantum materials and their interfaces by simultaneously probing charge, lattice, spin, and chemistry on the atomic scale with the sample held at temperatures ranging from room to cryogenic. However, its applications are currently limited by the instabilities of cryo-stages and electronics. To overcome this challenge, we develop an algorithm to effectively correct the complex distortions present in atomic resolution cryogenic 4D-STEM data sets. This method uses nonrigid registration to identify localized distortions in a 4D-STEM and relate them to an undistorted experimental STEM image, followed by a series of affine transformations for distortion corrections. This method allows a minimum loss of information in both reciprocal and real spaces, enabling the reconstruction of sample information from 4D-STEM data sets. This method is computationally cheap, fast, and applicable for on-the-fly data analysis in future in situ cryogenic 4D-STEM experiments.
TL;DR: In this paper , a representative 2D material, monolayer hexagonal boron nitride (hBN), was synthesized by epitaxial chemical vapor deposition and varied the growth parameters to regulate the hBN domain sizes.
Abstract: Wafer-scale monolayer two-dimensional (2D) materials have been realized by epitaxial chemical vapor deposition (CVD) in recent years. To scale up the synthesis of 2D materials, a systematic analysis of how the growth dynamics depend on the growth parameters is essential to unravel its mechanisms. However, the studies of CVD-grown 2D materials mostly adopted the control variate method and considered each parameter as an independent variable, which is not comprehensive for 2D materials growth optimization. Herein, we synthesized a representative 2D material, monolayer hexagonal boron nitride (hBN), on single-crystalline Cu (111) by epitaxial chemical vapor deposition and varied the growth parameters to regulate the hBN domain sizes. Furthermore, we explored the correlation between two growth parameters and provided the growth windows for large flake sizes by the Gaussian process. This new analysis approach based on machine learning provides a more comprehensive understanding of the growth mechanism for 2D materials.
07 Mar 2023
TL;DR: In this paper , the authors performed a systematic investigation of the correlation between the layer stacking, structure transition, magnetic and thermal transport properties of different α-RuCl$_3$ crystals with T$_N$ varying from 6\,K to 7.6
Abstract: We performed a systematic investigation of the correlation between the layer stacking, structure transition, magnetic and thermal transport properties of different $\alpha$-RuCl$_3$ crystals with T$_N$ varying from 6\,K to 7.6\,K by measuring magnetic properties, specific heat, neutron single crystal diffraction, and thermal transport. A small population of stacking disorder suppresses T$_N$. $\alpha$-RuCl$_3$ crystals with a single T$_N$ in the range of 7.4\,K-7.6 K have minimal amount of stacking disorder and show a well defined structure transition around 140\,K upon cooling. For those crystals with T$_N$ below 7\,K, the structure transition occurs well below 140\,K upon cooling and is incomplete, manifested by the coexistence of both high temperature and low temperature phases down to the lowest measurement temperature. Diffuse streaks were observed for these crystals but not for those with T$_N$ above 7.4\,K. For both types of crystals, oscillatory field dependent thermal conductivity and plateau-like feature in thermal Hall resistivity were observed in the field-induced disordered state that may be a quantum spin liquid. However, $\alpha$-RuCl$_3$ crystals with with minimal amount of stacking disorder have a higher thermal conductivity that pushes the thermal Hall conductivity to be close to the half-integer quantized value. Our results demonstrate a strong correlation between the layer stacking, structure transition, magnetic and thermal transport properties, and highlight the importance of interlayer coupling in $\alpha$-RuCl$_3$ despite the weak van der Waals bonding.
TL;DR: In this article , a targeted sampling strategy was proposed to increase the efficiency of STEM simulations through a new approach to independently subsample each frozen phonon layer, which can be used to seed the acquisition of real data, to potentially lead the way to self-driving (correcting) STEM.
Abstract: Scanning transmission electron microscopy images can be complex to interpret on the atomic scale as the contrast is sensitive to multiple factors such as sample thickness, composition, defects and aberrations. Simulations are commonly used to validate or interpret real experimental images, but they come at a cost of either long computation times or specialist hardware such as graphics processing units. Recent works in compressive sensing for experimental STEM images have shown that it is possible to significantly reduce the amount of acquired signal and still recover the full image without significant loss of image quality, and therefore it is proposed here that similar methods can be applied to STEM simulations. In this paper, we demonstrate a method that can significantly increase the efficiency of STEM simulations through a targeted sampling strategy, along with a new approach to independently subsample each frozen phonon layer. We show the effectiveness of this method by simulating a SrTiO3 grain boundary and monolayer 2H‐MoS2 containing a sulphur vacancy using the abTEM software. We also show how this method is not limited to only traditional multislice methods, but also increases the speed of the PRISM simulation method. Furthermore, we discuss the possibility for STEM simulations to seed the acquisition of real data, to potentially lead the way to self‐driving (correcting) STEM.
TL;DR: A review of the existing and emergent techniques for observing catalysts using S/TEM is presented in this article , where challenges and opportunities highlighted aim to inspire and accelerate the use of electron microscopy to further investigate the complex interplay of catalytic systems.
Abstract: Catalysts are the primary facilitator in many dynamic processes. Therefore, a thorough understanding of these processes has vast implications for a myriad of energy systems. The scanning/transmission electron microscope (S/TEM) is a powerful tool not only for atomic-scale characterization but also in situ catalytic experimentation. Techniques such as liquid and gas phase electron microscopy allow the observation of catalysts in an environment conducive to catalytic reactions. Correlated algorithms can greatly improve microscopy data processing and expand multidimensional data handling. Furthermore, new techniques including 4D-STEM, atomic electron tomography, cryogenic electron microscopy, and monochromated electron energy loss spectroscopy (EELS) push the boundaries of our comprehension of catalyst behavior. In this review, we discuss the existing and emergent techniques for observing catalysts using S/TEM. Challenges and opportunities highlighted aim to inspire and accelerate the use of electron microscopy to further investigate the complex interplay of catalytic systems.
28 Feb 2023
TL;DR: In this article , the authors demonstrate that a bulk crystal with subtle periodic modulations in its structure is transparent and positive-uniaxial, with extraordinary index n/e = 4.5 and ordinary index n_o = 2.4 in the mid- to far-infrared.
Abstract: In modern optics, materials with large birefringence ({\Delta}n, where n is the refractive index) are sought after for polarization control (e.g. in wave plates, polarizing beam splitters, etc.), nonlinear optics and quantum optics (e.g. for phase matching and production of entangled photons), micromanipulation, and as a platform for unconventional light-matter coupling, such as Dyakonov-like surface polaritons and hyperbolic phonon polaritons. Layered"van der Waals"materials, with strong intra-layer bonding and weak inter-layer bonding, can feature some of the largest optical anisotropy; however, their use in most optical systems is limited because their optic axis is out of the plane of the layers and the layers are weakly attached, making the anisotropy hard to access. Here, we demonstrate that a bulk crystal with subtle periodic modulations in its structure -- Sr9/8TiS3 -- is transparent and positive-uniaxial, with extraordinary index n_e = 4.5 and ordinary index n_o = 2.4 in the mid- to far-infrared. The excess Sr, compared to stoichiometric SrTiS3, results in the formation of TiS6 trigonal-prismatic units that break the infinite chains of face-shared TiS6 octahedra in SrTiS3 into periodic blocks of five TiS6 octahedral units. The additional electrons introduced by the excess Sr subsequently occupy the TiS6 octahedral blocks to form highly oriented and polarizable electron clouds, which selectively boost the extraordinary index n_e and result in record birefringence ({\Delta}n>2.1 with low loss). The connection between subtle structural modulations and large changes in refractive index suggests new categories of anisotropic materials and also tunable optical materials with large refractive-index modulation and low optical losses.
TL;DR: Song et al. as mentioned in this paper proposed a Z-scheme heterojunction TiO2/Ti-MOF-Pt with selectively anchored high-density Pt single-atomic cocatalysts for photocatalytic hydrogen evolution.
Abstract: Photocatalysis. The synthesis of a Z-scheme heterojunction TiO2/Ti-MOF-Pt with selectively anchored high-density Pt single-atomic cocatalysts for photocatalytic hydrogen evolution is reported by Chunshan Song, Xiang Wang, Xinwen Guo et al. in their Research Article (e202217439).
TL;DR: In this article , a multielement alloy nanoparticle catalyst with dispersed Ru (Ru-MEA) with other synergistic components (Cu, Pd, Pt) is presented.
Abstract: Electrochemical reduction of nitrate to ammonia (NH3) converts an environmental pollutant to a critical nutrient. However, current electrochemical nitrate reduction operations based on monometallic and bimetallic catalysts are limited in NH3 selectivity and catalyst stability, especially in acidic environments. Meanwhile, catalysts with dispersed active sites generally exhibit a higher atomic utilization and distinct activity. Herein, we report a multielement alloy nanoparticle catalyst with dispersed Ru (Ru-MEA) with other synergistic components (Cu, Pd, Pt). Density functional theory elucidated the synergy effect of Ru-MEA than Ru, where a better reactivity (NH3 partial current density of -50.8 mA cm-2) and high NH3 faradaic efficiency (93.5%) is achieved in industrially relevant acidic wastewater. In addition, the Ru-MEA catalyst showed good stability (e.g., 19.0% decay in FENH3 in three hours). This work provides a potential systematic and efficient catalyst discovery process that integrates a data-guided catalyst design and novel catalyst synthesis for a range of applications.
TL;DR: In this paper , the authors developed a method to obtain stable RhCx (x≈0.5) by introducing C atoms into the interstitial sites of well-defined Rh nanosheets of 8-10 atomic layers in thickness, and further elucidated the electronic and geometric effects of interstitial C atoms on the cleavage of C-C bond.
TL;DR: In this paper , the authors show that structural information beyond the diffraction limit and chemical information from the material can be extracted together, resulting in simultaneous multi-modal measurements, adding the additional dimensions of spectral information to 4D datasets.
Abstract: With the recent development of high-acquisition-speed pixelated detectors, 4D scanning transmission electron microscopy (4D-STEM) is becoming routinely available in high-resolution electron microscopy. 4D-STEM acts as a "universal" method that provides local information on materials that is challenging to extract from bulk techniques. It extends conventional STEM imaging to include super-resolution techniques and to provide quantitative phase-based information, such as differential phase contrast, psychography, or Bloch wave phase retrieval. However, an important missing factor is the chemical and bonding information provided by electron energy loss spectroscopy (EELS). 4D-STEM and EELS cannot currently be acquired simultaneously due to the overlapping geometry of the detectors. Here, the feasibility of modifying the detector geometry to overcome this challenge for bulk specimens is demonstrated, and the use of a partial or defective detector for ptycholgaphic structural imaging is explored. Results show that structural information beyond the diffraction-limit and chemical information from the material can be extracted together, resulting in simultaneous multi-modal measurements, adding the additional dimensions of spectral information to 4D datasets.
TL;DR: In this paper , the successful synthesis of well-defined ≈2nm Pt, PtSn, and Pt3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing PtSn and fcc Pt3Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed.
Abstract: The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt-Sn phase. Colloidal chemistry offers a route for the synthesis of Pt-Sn bimetallic nanoparticles (NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2 nm Pt, PtSn, and Pt3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing (hcp) PtSn and fcc Pt3 Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, face centred cubic (fcc) Pt3 Sn/Al2 O3 , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L12 -ordered superlattice. Contrary to PtSn, H2 cofeeding has no effect on the Pt3 Sn deactivation rate. The results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure-performance relationship on emerging bimetallic systems.